This is v5 of this series. The four previous submissions can be found
here [1], here [2], here[3], and here [4]. This version addresses the
comments received in v4 plus improvements of the handling of emulation
in 64-bit builds. Please see details in the change log.
=== What is UMIP?
User-Mode Instruction Prevention (UMIP) is a security feature present in
new Intel Processors. If enabled, it prevents the execution of certain
instructions if the Current Privilege Level (CPL) is greater than 0. If
these instructions were executed while in CPL > 0, user space applications
could have access to system-wide settings such as the global and local
descriptor tables, the segment selectors to the current task state and the
local descriptor table.
These are the instructions covered by UMIP:
* SGDT - Store Global Descriptor Table
* SIDT - Store Interrupt Descriptor Table
* SLDT - Store Local Descriptor Table
* SMSW - Store Machine Status Word
* STR - Store Task Register
If any of these instructions is executed with CPL > 0, a general protection
exception is issued when UMIP is enabled.
=== How does it impact applications?
There is a caveat, however. Certain applications rely on some of these
instructions to function. An example of this are applications that use
WineHQ[6]. For instance, these applications rely on sidt returning a non-
accessible memory location[6]. During the discussions, it was proposed that
the fault could be relied to the user-space and perform the emulation in
user-mode. However, this would break existing applications until, for
instance, they update to a new WineHQ version. However, this approach
would require UMIP to be disabled by default. The consensus in this forum
is to always enable it.
This patchset initially treated tasks running in virtual-8086 mode as a
special case. However, I received clarification that DOSEMU[7] does not
support applications that use these instructions. It relies on WineHQ for
this [8]. Furthermore, the applications for which the concern was raised
run in protected mode [6].
Please note that UMIP is always enabled for both 64-bit and 32-bit Linux
builds. However, emulation of the UMIP-protected instructions is not done
for 64-bit processes. 64-bit user space applications will receive the
SIGSEGV signal when UMIP instructions causes a general protection fault.
=== How are UMIP-protected instructions emulated?
This version keeps UMIP enabled at all times and by default. If a general
protection fault caused by the instructions protected by UMIP is
detected, such fault will be fixed-up by returning dummy values as follows:
* SGDT and SIDT return hard-coded dummy values as the base of the global
descriptor and interrupt descriptor tables. These hard-coded values
correspond to memory addresses that are near the end of the kernel
memory map. This is also the case for virtual-8086 mode tasks. In all
my experiments in x86_32, the base of GDT and IDT was always a 4-byte
address, even for 16-bit operands. Thus, my emulation code does the
same. In all cases, the limit of the table is set to 0.
* STR and SLDT return 0 as the segment selector. This looks appropriate
since we are providing a dummy value as the base address of the global
descriptor table.
* SMSW returns the value with which the CR0 register is programmed in
head_32/64.S at boot time. This is, the following bits are enabled:
CR0.0 for Protection Enable, CR.1 for Monitor Coprocessor, CR.4 for
Extension Type, which will always be 1 in recent processors with UMIP;
CR.5 for Numeric Error, CR0.16 for Write Protect, CR0.18 for Alignment
Mask. As per the Intel 64 and IA-32 Architectures Software Developer's
Manual, SMSW returns a 16-bit results for memory operands. However, when
the operand is a register, the results can be up to CR0[63:0]. Since
the emulation code only kicks-in in x86_32, we return up to CR[31:0].
* The proposed emulation code is handles faults that happens in both
protected and virtual-8086 mode.
=== How is this series laid out?
++ Fix bugs in MPX address evaluator
I found very useful the code for Intel MPX (Memory Protection Extensions)
used to parse opcodes and the memory locations contained in the general
purpose registers when used as operands. I put some of this code in
a separate library file that both MPX and UMIP can access and avoid code
duplication. Before creating the new library, I fixed a couple of bugs
that I found in how MPX determines the address contained in the
instruction and operands.
++ Provide a new x86 instruction evaluating library
With bugs fixed, the MPX evaluating code is relocated in a new insn-eval.c
library. The basic functionality of this library is extended to obtain the
segment descriptor selected by either segment override prefixes or the
default segment by the involved registers in the calculation of the
effective address. It was also extended to obtain the default address and
operand sizes as well as the segment base address. Also, support to
process 16-bit address encodings. Armed with this arsenal, it is now
possible to determine the linear address onto which the emulated results
shall be copied.
This code supports Normal 32-bit and 64-bit (i.e., __USER32_CS and/or
__USER_CS) protected mode, virtual-8086 mode, 16-bit protected mode with
32-bit base address.
++ Emulate UMIP instructions
A new fixup_umip_exception functions inspect the instruction at the
instruction pointer. If it is an UMIP-protected instruction, it executes
the emulation code. This uses all the address-computing code of the
previous section.
++ Add self-tests
Lastly, self-tests are added to entry_from_v86.c to exercise the most
typical use cases of UMIP-protected instructions in a virtual-8086 mode.
++ Extensive tests
Extensive tests were performed to test all the combinations of ModRM,
SiB and displacements for 16-bit and 32-bit encodings for the ss, ds,
es and fs segments. Tests also include a 64-bit program that uses
segmentation via FS and GS. For this purpose, I temporarily, and not
as part of this patchset, enabled UMIP support for 64-bit process with
the intention to test the computations of linear addresses in 64-bit
mode, including the extra R8-R15 registers. Extensive test is also
implemented for virtual-8086 tasks. Code of these tests can be found here
[9] and here [10].
[1]. https://lwn.net/Articles/705877/
[2]. https://lkml.org/lkml/2016/12/23/265
[3]. https://lkml.org/lkml/2017/1/25/622
[4]. https://lkml.org/lkml/2017/2/23/40
[5]. https://www.winehq.org/
[6]. https://www.winehq.org/pipermail/wine-devel/2016-November/115320.html
[7]. http://www.dosemu.org/
[8]. http://marc.info/?l=linux-kernel&m=147876798717927&w=2
[9]. https://github.com/01org/luv-yocto/tree/rneri/umip/meta-luv/recipes-core/umip/files
[10]. https://github.com/01org/luv-yocto/commit/a72a7fe7d68693c0f4100ad86de6ecabde57334f#diff-3860c136a63add269bce4ea50222c248R1
Thanks and BR,
Ricardo
Changes since V4:
* Audited patches to use braces in all the branches of conditional.
statements, except those in which the conditional action only takes one
line.
* Implemented support in 64-builds for both 32-bit and 64-bit tasks in the
instruction evaluating library.
* Split segment selector function in the instruction evaluating library
into two functions to resolve the segment type by instruction override
or default and a separate function to actually read the segment selector.
* Fixed a bug when evaluating 32-bit effective addresses with 64-bit
kernels.
* Split patches further for for easier review.
* Use signed variables for computation of effective address.
* Fixed issue with a spurious static modifier in function insn_get_addr_ref
found by kbuild test bot.
* Removed comparison between true and fixup_umip_exception.
* Reworked check logic when identifying erroneous vs invalid values of the
SiB base and index.
Changes since V3:
* Limited emulation to 32-bit and 16-bit modes. For 64-bit mode, a general
protection fault is still issued when UMIP-protected instructions are
executed with CPL > 0.
* Expanded instruction-evaluating code to obtain segment descriptor along
with their attributes such as base address and default address and
operand sizes. Also, support for 16-bit encodings in protected mode was
implemented.
* When getting a segment descriptor, this include support to obtain those
of a local descriptor table.
* Now the instruction-evaluating code returns -EDOM when the value of
registers should not be used in calculating the effective address. The
value -EINVAL is left for errors.
* Incorporate the value of the segment base address in the computation of
linear addresses.
* Renamed new instruction evaluation library from insn-kernel.c to
insn-eval.c
* Exported functions insn_get_reg_offset_* to obtain the register offset
by ModRM r/m, SiB base and SiB index.
* Improved documentation of functions.
* Split patches further for easier review.
Changes since V2:
* Added new utility functions to decode the memory addresses contained in
registers when the 16-bit addressing encodings are used. This includes
code to obtain and compute memory addresses using segment selectors for
real-mode address translation.
* Added support to emulate UMIP-protected instructions for virtual-8086
tasks.
* Added self-tests for virtual-8086 mode that contains representative
use cases: address represented as a displacement, address in registers
and registers as operands.
* Instead of maintaining a static variable for the dummy base addresses
of the IDT and GDT, a hard-coded value is used.
* The emulated SMSW instructions now return the value with which the CR0
register is programmed in head_32/64.S This is: PE | MP | ET | NE | WP
| AM. For x86_64, PG is also enabled.
* The new file arch/x86/lib/insn-utils.c is now renamed as arch/x86/lib/
insn-kernel.c. It also has its own header. This helps keep in sync the
the kernel and objtool instruction decoders. Also, the new insn-kernel.c
contains utility functions that are only relevant in a kernel context.
* Removed printed warnings for errors that occur when decoding instructions
with invalid operands.
* Added more comments on fixes in the instruction-decoding MPX functions.
* Now user_64bit_mode(regs) is used instead of test_thread_flag(TIF_IA32)
to determine if the task is 32-bit or 64-bit.
* Found and fixed a bug in insn-decoder in which X86_MODRM_RM was
incorrectly used to obtain the mod part of the ModRM byte.
* Added more explanatory code in emulation and instruction decoding code.
This includes a comment regarding that copy_from_user could fail if there
exists a memory protection key in place.
* Tested code with CONFIG_X86_DECODER_SELFTEST=y and everything passes now.
* Prefixed get_reg_offset_rm with insn_ as this function is exposed
via a header file. For clarity, this function was added in a separate
patch.
Changes since V1:
* Virtual-8086 mode tasks are not treated in a special manner. All code
for this purpose was removed.
* Instead of attempting to disable UMIP during a context switch or when
entering virtual-8086 mode, UMIP remains enabled all the time. General
protection faults that occur are fixed-up by returning dummy values as
detailed above.
* Removed umip= kernel parameter in favor of using clearcpuid=514 to
disable UMIP.
* Removed selftests designed to detect the absence of SIGSEGV signals when
running in virtual-8086 mode.
* Reused code from MPX to decode instructions operands. For this purpose
code was put in a common location.
* Fixed two bugs in MPX code that decodes operands.
Thanks and BR,
Ricardo
Ricardo Neri (20):
x86/mpx: Use signed variables to compute effective addresses
x86/mpx: Do not use SIB index if index points to R/ESP
x86/mpx: Do not use R/EBP as base in the SIB byte with Mod = 0
x86/mpx, x86/insn: Relocate insn util functions to a new insn-kernel
x86/insn-eval: Add utility functions to get register offsets
x86/insn-eval: Add utility functions to get segment selector
x86/insn-eval: Add utility function to get segment descriptor
x86/insn-eval: Add utility function to get segment descriptor base
address
x86/insn-eval: Add functions to get default operand and address sizes
x86/insn-eval: Do not use R/EBP as base if mod in ModRM is zero
insn/eval: Incorporate segment base in address computation
x86/insn: Support both signed 32-bit and 64-bit effective addresses
x86/insn-eval: Add support to resolve 16-bit addressing encodings
x86/insn-eval: Add wrapper function for 16-bit and 32-bit address
encodings
x86/cpufeature: Add User-Mode Instruction Prevention definitions
x86: Add emulation code for UMIP instructions
x86/umip: Force a page fault when unable to copy emulated result to
user
x86/traps: Fixup general protection faults caused by UMIP
x86: Enable User-Mode Instruction Prevention
selftests/x86: Add tests for User-Mode Instruction Prevention
arch/x86/Kconfig | 10 +
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/disabled-features.h | 8 +-
arch/x86/include/asm/insn-eval.h | 23 +
arch/x86/include/asm/umip.h | 15 +
arch/x86/include/uapi/asm/processor-flags.h | 2 +
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/cpu/common.c | 16 +-
arch/x86/kernel/traps.c | 4 +
arch/x86/kernel/umip.c | 305 ++++++++++
arch/x86/lib/Makefile | 2 +-
arch/x86/lib/insn-eval.c | 832 ++++++++++++++++++++++++++
arch/x86/mm/mpx.c | 120 +---
tools/testing/selftests/x86/entry_from_vm86.c | 39 +-
14 files changed, 1256 insertions(+), 122 deletions(-)
create mode 100644 arch/x86/include/asm/insn-eval.h
create mode 100644 arch/x86/include/asm/umip.h
create mode 100644 arch/x86/kernel/umip.c
create mode 100644 arch/x86/lib/insn-eval.c
--
2.9.3
User_mode Instruction Prevention (UMIP) is enabled by setting/clearing a
bit in %cr4.
It makes sense to enable UMIP at some point while booting, before user
spaces come up. Like SMAP and SMEP, is not critical to have it enabled
very early during boot. This is because UMIP is relevant only when there is
a userspace to be protected from. Given the similarities in relevance, it
makes sense to enable UMIP along with SMAP and SMEP.
UMIP is enabled by default. It can be disabled by adding clearcpuid=514
to the kernel parameters.
Cc: Andy Lutomirski <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Chen Yucong <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Fenghua Yu <[email protected]>
Cc: Huang Rui <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Liang Z. Li <[email protected]>
Cc: Alexandre Julliard <[email protected]>
Cc: Stas Sergeev <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/Kconfig | 10 ++++++++++
arch/x86/kernel/cpu/common.c | 16 +++++++++++++++-
2 files changed, 25 insertions(+), 1 deletion(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index cc98d5a..b7f1226 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1735,6 +1735,16 @@ config X86_SMAP
If unsure, say Y.
+config X86_INTEL_UMIP
+ def_bool y
+ depends on CPU_SUP_INTEL
+ prompt "Intel User Mode Instruction Prevention" if EXPERT
+ ---help---
+ The User Mode Instruction Prevention (UMIP) is a security
+ feature in newer Intel processors. If enabled, a general
+ protection fault is issued if the instructions SGDT, SLDT,
+ SIDT, SMSW and STR are executed in user mode.
+
config X86_INTEL_MPX
prompt "Intel MPX (Memory Protection Extensions)"
def_bool n
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 58094a1..9f59eb5 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -311,6 +311,19 @@ static __always_inline void setup_smap(struct cpuinfo_x86 *c)
}
}
+static __always_inline void setup_umip(struct cpuinfo_x86 *c)
+{
+ if (cpu_feature_enabled(X86_FEATURE_UMIP) &&
+ cpu_has(c, X86_FEATURE_UMIP))
+ cr4_set_bits(X86_CR4_UMIP);
+ else
+ /*
+ * Make sure UMIP is disabled in case it was enabled in a
+ * previous boot (e.g., via kexec).
+ */
+ cr4_clear_bits(X86_CR4_UMIP);
+}
+
/*
* Protection Keys are not available in 32-bit mode.
*/
@@ -1080,9 +1093,10 @@ static void identify_cpu(struct cpuinfo_x86 *c)
/* Disable the PN if appropriate */
squash_the_stupid_serial_number(c);
- /* Set up SMEP/SMAP */
+ /* Set up SMEP/SMAP/UMIP */
setup_smep(c);
setup_smap(c);
+ setup_umip(c);
/*
* The vendor-specific functions might have changed features.
--
2.9.3
When computing a linear address and segmentation is used, we need to know
the base address of the segment involved in the computation. In most of
the cases, the segment base address will be zero as in USER_DS/USER32_DS.
However, it may be possible that a user space program defines its own
segments via a local descriptor table. In such a case, the segment base
address may not be zero .Thus, the segment base address is needed to
calculate correctly the linear address.
The segment selector to be used when computing a linear address is
determined by either any of segment select override prefixes in the
instruction or inferred from the registers involved in the computation of
the effective address; in that order. Also, there are cases when the
overrides shall be ignored.
For clarity, this process can be split into two steps: resolving the
relevant segment and, once known, read the applicable segment selector.
The method to obtain the segment selector depends on several factors. In
32-bit builds, segment selectors are saved into the pt_regs structure
when switching to kernel mode. The same is also true for virtual-8086
mode. In 64-bit builds, segmentation is mostly ignored, except when
running a program in 32-bit legacy mode. In this case, CS and SS can be
obtained from pt_regs. DS, ES, FS and GS can be read directly from
registers. Lastly, segmentation is possible in 64-bit mode via FS and GS.
In these two cases, base addresses are obtained from the relevant MSRs.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Thomas Garnier <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/lib/insn-eval.c | 195 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 195 insertions(+)
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 78df1c9..8d45df8 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -8,6 +8,7 @@
#include <asm/inat.h>
#include <asm/insn.h>
#include <asm/insn-eval.h>
+#include <asm/vm86.h>
enum reg_type {
REG_TYPE_RM = 0,
@@ -15,6 +16,200 @@ enum reg_type {
REG_TYPE_BASE,
};
+enum segment {
+ SEG_CS = 0x23,
+ SEG_SS = 0x36,
+ SEG_DS = 0x3e,
+ SEG_ES = 0x26,
+ SEG_FS = 0x64,
+ SEG_GS = 0x65
+};
+
+/**
+ * resolve_seg_selector() - obtain segment selector
+ * @regs: Set of registers containing the segment selector
+ * @insn: Instruction structure with selector override prefixes
+ * @regoff: Operand offset, in pt_regs, of which the selector is needed
+ * @default: Resolve default segment selector (i.e., ignore overrides)
+ *
+ * The segment selector to which an effective address refers depends on
+ * a) segment selector overrides instruction prefixes or b) the operand
+ * register indicated in the ModRM or SiB byte.
+ *
+ * For case a), the function inspects any prefixes in the insn instruction;
+ * insn can be null to indicate that selector override prefixes shall be
+ * ignored. This is useful when the use of prefixes is forbidden (e.g.,
+ * obtaining the code selector). For case b), the operand register shall be
+ * represented as the offset from the base address of pt_regs. Also, regoff
+ * can be -EINVAL for cases in which registers are not used as operands (e.g.,
+ * when the mod and r/m parts of the ModRM byte are 0 and 5, respectively).
+ *
+ * This function returns the segment selector to utilize as per the conditions
+ * described above. Please note that this functin does not return the value
+ * of the segment selector. The value of the segment selector needs to be
+ * obtained using get_segment_selector and passing the segment selector type
+ * resolved by this function.
+ *
+ * Return: Segment selector to use, among CS, SS, DS, ES, FS or GS.
+ */
+static int resolve_seg_selector(struct insn *insn, int regoff, bool get_default)
+{
+ int i;
+
+ if (!insn)
+ return -EINVAL;
+
+ if (get_default)
+ goto default_seg;
+ /*
+ * Check first if we have selector overrides. Having more than
+ * one selector override leads to undefined behavior. We
+ * only use the first one and return
+ */
+ for (i = 0; i < insn->prefixes.nbytes; i++) {
+ switch (insn->prefixes.bytes[i]) {
+ case SEG_CS:
+ return SEG_CS;
+ case SEG_SS:
+ return SEG_SS;
+ case SEG_DS:
+ return SEG_DS;
+ case SEG_ES:
+ return SEG_ES;
+ case SEG_FS:
+ return SEG_FS;
+ case SEG_GS:
+ return SEG_GS;
+ default:
+ return -EINVAL;
+ }
+ }
+
+default_seg:
+ /*
+ * If no overrides, use default selectors as described in the
+ * Intel documentation: SS for ESP or EBP. DS for all data references,
+ * except when relative to stack or string destination.
+ * Also, AX, CX and DX are not valid register operands in 16-bit
+ * address encodings.
+ * Callers must interpret the result correctly according to the type
+ * of instructions (e.g., use ES for string instructions).
+ * Also, some values of modrm and sib might seem to indicate the use
+ * of EBP and ESP (e.g., modrm_mod = 0, modrm_rm = 5) but actually
+ * they refer to cases in which only a displacement used. These cases
+ * should be indentified by the caller and not with this function.
+ */
+ switch (regoff) {
+ case offsetof(struct pt_regs, ax):
+ /* fall through */
+ case offsetof(struct pt_regs, cx):
+ /* fall through */
+ case offsetof(struct pt_regs, dx):
+ if (insn && insn->addr_bytes == 2)
+ return -EINVAL;
+ case -EDOM: /* no register involved in address computation */
+ case offsetof(struct pt_regs, bx):
+ /* fall through */
+ case offsetof(struct pt_regs, di):
+ /* fall through */
+ case offsetof(struct pt_regs, si):
+ return SEG_DS;
+ case offsetof(struct pt_regs, bp):
+ /* fall through */
+ case offsetof(struct pt_regs, sp):
+ return SEG_SS;
+ case offsetof(struct pt_regs, ip):
+ return SEG_CS;
+ default:
+ return -EINVAL;
+ }
+}
+
+/**
+ * get_segment_selector() - obtain segment selector
+ * @regs: Set of registers containing the segment selector
+ * @seg_type: Type of segment selector to obtain
+ * @regoff: Operand offset, in pt_regs, of which the selector is needed
+ *
+ * Obtain the segment selector for any of CS, SS, DS, ES, FS, GS. In
+ * CONFIG_X86_32, the segment is obtained from either pt_regs or
+ * kernel_vm86_regs as applicable. In CONFIG_X86_64, CS and SS are obtained
+ * from pt_regs. DS, ES, FS and GS are obtained by reading the ds and es, fs
+ * and gs, respectively.
+ *
+ * Return: Value of the segment selector
+ */
+static unsigned short get_segment_selector(struct pt_regs *regs,
+ enum segment seg_type)
+{
+#ifdef CONFIG_X86_64
+ unsigned short seg_sel;
+
+ switch (seg_type) {
+ case SEG_CS:
+ return (unsigned short)(regs->cs & 0xffff);
+ case SEG_SS:
+ return (unsigned short)(regs->ss & 0xffff);
+ case SEG_DS:
+ savesegment(ds, seg_sel);
+ return seg_sel;
+ case SEG_ES:
+ savesegment(es, seg_sel);
+ return seg_sel;
+ case SEG_FS:
+ savesegment(fs, seg_sel);
+ return seg_sel;
+ case SEG_GS:
+ savesegment(gs, seg_sel);
+ return seg_sel;
+ default:
+ return -1;
+ }
+#else /* CONFIG_X86_32 */
+ struct kernel_vm86_regs *vm86regs = (struct kernel_vm86_regs *)regs;
+
+ if (v8086_mode(regs)) {
+ switch (seg_type) {
+ case SEG_CS:
+ return (unsigned short)(regs->cs & 0xffff);
+ case SEG_SS:
+ return (unsigned short)(regs->ss & 0xffff);
+ case SEG_DS:
+ return vm86regs->ds;
+ case SEG_ES:
+ return vm86regs->es;
+ case SEG_FS:
+ return vm86regs->fs;
+ case SEG_GS:
+ return vm86regs->gs;
+ default:
+ return -1;
+ }
+ }
+
+ switch (seg_type) {
+ case SEG_CS:
+ return (unsigned short)(regs->cs & 0xffff);
+ case SEG_SS:
+ return (unsigned short)(regs->ss & 0xffff);
+ case SEG_DS:
+ return (unsigned short)(regs->ds & 0xffff);
+ case SEG_ES:
+ return (unsigned short)(regs->es & 0xffff);
+ case SEG_FS:
+ return (unsigned short)(regs->fs & 0xffff);
+ case SEG_GS:
+ /*
+ * GS may or may not be in regs as per CONFIG_X86_32_LAZY_GS.
+ * The macro below takes care of both cases.
+ */
+ return get_user_gs(regs);
+ default:
+ return -1;
+ }
+#endif /* CONFIG_X86_64 */
+}
+
static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
enum reg_type type)
{
--
2.9.3
Other kernel submodules can benefit from using the utility functions
defined in mpx.c to obtain the addresses and values of operands contained
in the general purpose registers. An instance of this is the emulation code
used for instructions protected by the Intel User-Mode Instruction
Prevention feature.
Thus, these functions are relocated to a new insn-eval.c file. The reason
to not relocate these utilities into insn.c is that the latter solely
analyses instructions given by a struct insn without any knowledge of the
meaning of the values of instruction operands. This new utility insn-
eval.c aims to be used to resolve effective and userspace linear addresses
based on the contents of the instruction operands as well as the contents
of pt_regs structure.
These utilities come with a separate header. This is to avoid taking insn.c
out of sync from the instructions decoders under tools/obj and tools/perf.
This also avoids adding cumbersome #ifdef's for the #include'd files
required to decode instructions in a kernel context.
Functions are simply relocated. There are not functional or indentation
changes.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Thomas Garnier <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/include/asm/insn-eval.h | 16 ++++
arch/x86/lib/Makefile | 2 +-
arch/x86/lib/insn-eval.c | 160 +++++++++++++++++++++++++++++++++++++++
arch/x86/mm/mpx.c | 153 +------------------------------------
4 files changed, 179 insertions(+), 152 deletions(-)
create mode 100644 arch/x86/include/asm/insn-eval.h
create mode 100644 arch/x86/lib/insn-eval.c
diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
new file mode 100644
index 0000000..5cab1b1
--- /dev/null
+++ b/arch/x86/include/asm/insn-eval.h
@@ -0,0 +1,16 @@
+#ifndef _ASM_X86_INSN_EVAL_H
+#define _ASM_X86_INSN_EVAL_H
+/*
+ * A collection of utility functions for x86 instruction analysis to be
+ * used in a kernel context. Useful when, for instance, making sense
+ * of the registers indicated by operands.
+ */
+
+#include <linux/compiler.h>
+#include <linux/bug.h>
+#include <linux/err.h>
+#include <asm/ptrace.h>
+
+void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs);
+
+#endif /* _ASM_X86_INSN_EVAL_H */
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 34a7413..675d7b0 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -23,7 +23,7 @@ lib-y := delay.o misc.o cmdline.o cpu.o
lib-y += usercopy_$(BITS).o usercopy.o getuser.o putuser.o
lib-y += memcpy_$(BITS).o
lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
-lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o
+lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o insn-eval.o
lib-$(CONFIG_RANDOMIZE_BASE) += kaslr.o
obj-y += msr.o msr-reg.o msr-reg-export.o hweight.o
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
new file mode 100644
index 0000000..23cf010
--- /dev/null
+++ b/arch/x86/lib/insn-eval.c
@@ -0,0 +1,160 @@
+/*
+ * Utility functions for x86 operand and address decoding
+ *
+ * Copyright (C) Intel Corporation 2017
+ */
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <asm/inat.h>
+#include <asm/insn.h>
+#include <asm/insn-eval.h>
+
+enum reg_type {
+ REG_TYPE_RM = 0,
+ REG_TYPE_INDEX,
+ REG_TYPE_BASE,
+};
+
+static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
+ enum reg_type type)
+{
+ int regno = 0;
+
+ static const int regoff[] = {
+ offsetof(struct pt_regs, ax),
+ offsetof(struct pt_regs, cx),
+ offsetof(struct pt_regs, dx),
+ offsetof(struct pt_regs, bx),
+ offsetof(struct pt_regs, sp),
+ offsetof(struct pt_regs, bp),
+ offsetof(struct pt_regs, si),
+ offsetof(struct pt_regs, di),
+#ifdef CONFIG_X86_64
+ offsetof(struct pt_regs, r8),
+ offsetof(struct pt_regs, r9),
+ offsetof(struct pt_regs, r10),
+ offsetof(struct pt_regs, r11),
+ offsetof(struct pt_regs, r12),
+ offsetof(struct pt_regs, r13),
+ offsetof(struct pt_regs, r14),
+ offsetof(struct pt_regs, r15),
+#endif
+ };
+ int nr_registers = ARRAY_SIZE(regoff);
+ /*
+ * Don't possibly decode a 32-bit instructions as
+ * reading a 64-bit-only register.
+ */
+ if (IS_ENABLED(CONFIG_X86_64) && !insn->x86_64)
+ nr_registers -= 8;
+
+ switch (type) {
+ case REG_TYPE_RM:
+ regno = X86_MODRM_RM(insn->modrm.value);
+ if (X86_REX_B(insn->rex_prefix.value))
+ regno += 8;
+ break;
+
+ case REG_TYPE_INDEX:
+ regno = X86_SIB_INDEX(insn->sib.value);
+ if (X86_REX_X(insn->rex_prefix.value))
+ regno += 8;
+ /*
+ * If mod !=3, register R/ESP (regno=4) is not used as index in
+ * the address computation. Check is done after looking at REX.X
+ * This is because R12 (regno=12) can be used as an index.
+ */
+ if (regno == 4 && X86_MODRM_MOD(insn->modrm.value) != 3)
+ return -EDOM;
+ break;
+
+ case REG_TYPE_BASE:
+ regno = X86_SIB_BASE(insn->sib.value);
+ /*
+ * If mod is 0 and register R/EBP (regno=5) is indicated in the
+ * base part of the SIB byte, the value of such register should
+ * not be used in the address computation. Also, a 32-bit
+ * displacement is expected in this case; the instruction
+ * decoder takes care of it. This is true for both R13 and
+ * R/EBP as REX.B will not be decoded.
+ */
+ if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0)
+ return -EDOM;
+
+ if (X86_REX_B(insn->rex_prefix.value))
+ regno += 8;
+ break;
+
+ default:
+ pr_err("invalid register type");
+ BUG();
+ break;
+ }
+
+ if (regno >= nr_registers) {
+ WARN_ONCE(1, "decoded an instruction with an invalid register");
+ return -EINVAL;
+ }
+ return regoff[regno];
+}
+
+/*
+ * return the address being referenced be instruction
+ * for rm=3 returning the content of the rm reg
+ * for rm!=3 calculates the address using SIB and Disp
+ */
+void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
+{
+ unsigned long linear_addr;
+ long eff_addr, base, indx;
+ int addr_offset, base_offset, indx_offset;
+ insn_byte_t sib;
+
+ insn_get_modrm(insn);
+ insn_get_sib(insn);
+ sib = insn->sib.value;
+
+ if (X86_MODRM_MOD(insn->modrm.value) == 3) {
+ addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
+ if (addr_offset < 0)
+ goto out_err;
+ eff_addr = regs_get_register(regs, addr_offset);
+ } else {
+ if (insn->sib.nbytes) {
+ /*
+ * Negative values in the base and index offset means
+ * an error when decoding the SIB byte. Except -EDOM,
+ * which means that the registers should not be used
+ * in the address computation.
+ */
+ base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
+ if (unlikely(base_offset == -EDOM))
+ base = 0;
+ else if (unlikely(base_offset < 0))
+ goto out_err;
+ else
+ base = regs_get_register(regs, base_offset);
+
+ indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
+ if (unlikely(indx_offset == -EDOM))
+ indx = 0;
+ else if (unlikely(indx_offset < 0))
+ goto out_err;
+ else
+ indx = regs_get_register(regs, indx_offset);
+
+ eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
+ } else {
+ addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
+ if (addr_offset < 0)
+ goto out_err;
+ eff_addr = regs_get_register(regs, addr_offset);
+ }
+ eff_addr += insn->displacement.value;
+ }
+ linear_addr = (unsigned long)eff_addr;
+
+ return (void __user *)linear_addr;
+out_err:
+ return (void __user *)-1;
+}
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index ef7eb67..4c3efd6 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -12,6 +12,7 @@
#include <linux/sched/sysctl.h>
#include <asm/insn.h>
+#include <asm/insn-eval.h>
#include <asm/mman.h>
#include <asm/mmu_context.h>
#include <asm/mpx.h>
@@ -60,156 +61,6 @@ static unsigned long mpx_mmap(unsigned long len)
return addr;
}
-enum reg_type {
- REG_TYPE_RM = 0,
- REG_TYPE_INDEX,
- REG_TYPE_BASE,
-};
-
-static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
- enum reg_type type)
-{
- int regno = 0;
-
- static const int regoff[] = {
- offsetof(struct pt_regs, ax),
- offsetof(struct pt_regs, cx),
- offsetof(struct pt_regs, dx),
- offsetof(struct pt_regs, bx),
- offsetof(struct pt_regs, sp),
- offsetof(struct pt_regs, bp),
- offsetof(struct pt_regs, si),
- offsetof(struct pt_regs, di),
-#ifdef CONFIG_X86_64
- offsetof(struct pt_regs, r8),
- offsetof(struct pt_regs, r9),
- offsetof(struct pt_regs, r10),
- offsetof(struct pt_regs, r11),
- offsetof(struct pt_regs, r12),
- offsetof(struct pt_regs, r13),
- offsetof(struct pt_regs, r14),
- offsetof(struct pt_regs, r15),
-#endif
- };
- int nr_registers = ARRAY_SIZE(regoff);
- /*
- * Don't possibly decode a 32-bit instructions as
- * reading a 64-bit-only register.
- */
- if (IS_ENABLED(CONFIG_X86_64) && !insn->x86_64)
- nr_registers -= 8;
-
- switch (type) {
- case REG_TYPE_RM:
- regno = X86_MODRM_RM(insn->modrm.value);
- if (X86_REX_B(insn->rex_prefix.value))
- regno += 8;
- break;
-
- case REG_TYPE_INDEX:
- regno = X86_SIB_INDEX(insn->sib.value);
- if (X86_REX_X(insn->rex_prefix.value))
- regno += 8;
- /*
- * If mod !=3, register R/ESP (regno=4) is not used as index in
- * the address computation. Check is done after looking at REX.X
- * This is because R12 (regno=12) can be used as an index.
- */
- if (regno == 4 && X86_MODRM_MOD(insn->modrm.value) != 3)
- return -EDOM;
- break;
-
- case REG_TYPE_BASE:
- regno = X86_SIB_BASE(insn->sib.value);
- /*
- * If mod is 0 and register R/EBP (regno=5) is indicated in the
- * base part of the SIB byte, the value of such register should
- * not be used in the address computation. Also, a 32-bit
- * displacement is expected in this case; the instruction
- * decoder takes care of it. This is true for both R13 and
- * R/EBP as REX.B will not be decoded.
- */
- if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0)
- return -EDOM;
-
- if (X86_REX_B(insn->rex_prefix.value))
- regno += 8;
- break;
-
- default:
- pr_err("invalid register type");
- BUG();
- break;
- }
-
- if (regno >= nr_registers) {
- WARN_ONCE(1, "decoded an instruction with an invalid register");
- return -EINVAL;
- }
- return regoff[regno];
-}
-
-/*
- * return the address being referenced be instruction
- * for rm=3 returning the content of the rm reg
- * for rm!=3 calculates the address using SIB and Disp
- */
-static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
-{
- unsigned long linear_addr;
- long eff_addr, base, indx;
- int addr_offset, base_offset, indx_offset;
- insn_byte_t sib;
-
- insn_get_modrm(insn);
- insn_get_sib(insn);
- sib = insn->sib.value;
-
- if (X86_MODRM_MOD(insn->modrm.value) == 3) {
- addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
- if (addr_offset < 0)
- goto out_err;
- eff_addr = regs_get_register(regs, addr_offset);
- } else {
- if (insn->sib.nbytes) {
- /*
- * Negative values in the base and index offset means
- * an error when decoding the SIB byte. Except -EDOM,
- * which means that the registers should not be used
- * in the address computation.
- */
- base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
- if (unlikely(base_offset == -EDOM))
- base = 0;
- else if (unlikely(base_offset < 0))
- goto out_err;
- else
- base = regs_get_register(regs, base_offset);
-
- indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
- if (unlikely(indx_offset == -EDOM))
- indx = 0;
- else if (unlikely(indx_offset < 0))
- goto out_err;
- else
- indx = regs_get_register(regs, indx_offset);
-
- eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
- } else {
- addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
- if (addr_offset < 0)
- goto out_err;
- eff_addr = regs_get_register(regs, addr_offset);
- }
- eff_addr += insn->displacement.value;
- }
- linear_addr = (unsigned long)eff_addr;
-
- return (void __user *)linear_addr;
-out_err:
- return (void __user *)-1;
-}
-
static int mpx_insn_decode(struct insn *insn,
struct pt_regs *regs)
{
@@ -322,7 +173,7 @@ siginfo_t *mpx_generate_siginfo(struct pt_regs *regs)
info->si_signo = SIGSEGV;
info->si_errno = 0;
info->si_code = SEGV_BNDERR;
- info->si_addr = mpx_get_addr_ref(&insn, regs);
+ info->si_addr = insn_get_addr_ref(&insn, regs);
/*
* We were not able to extract an address from the instruction,
* probably because there was something invalid in it.
--
2.9.3
The function insn_get_reg_offset takes as argument an enumeration that
indicates the type of offset that is returned: the R/M part of the ModRM
byte, the index of the SIB byte or the base of the SIB byte. Callers of
this function would need the definition of such enumeration. This is not
needed. Instead, helper functions can be defined for this purpose can be
added. These functions are useful in cases when, for instance, the caller
needs to decide whether the operand is a register or a memory location by
looking at the mod part of the ModRM byte.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Thomas Garnier <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/include/asm/insn-eval.h | 3 +++
arch/x86/lib/insn-eval.c | 51 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 54 insertions(+)
diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
index 5cab1b1..754211b 100644
--- a/arch/x86/include/asm/insn-eval.h
+++ b/arch/x86/include/asm/insn-eval.h
@@ -12,5 +12,8 @@
#include <asm/ptrace.h>
void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs);
+int insn_get_reg_offset_modrm_rm(struct insn *insn, struct pt_regs *regs);
+int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs);
+int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs);
#endif /* _ASM_X86_INSN_EVAL_H */
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 23cf010..78df1c9 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -98,6 +98,57 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
return regoff[regno];
}
+/**
+ * insn_get_reg_offset_modrm_rm - Obtain register in r/m part of ModRM byte
+ * @insn: Instruction structure containing the ModRM byte
+ * @regs: Set of registers indicated by the ModRM byte
+ *
+ * Obtain the register indicated by the r/m part of the ModRM byte. The
+ * register is obtained as an offset from the base of pt_regs. In specific
+ * cases, the returned value can be -EDOM to indicate that the particular value
+ * of ModRM does not refer to a register.
+ *
+ * Return: Register indicated by r/m, as an offset within struct pt_regs
+ */
+int insn_get_reg_offset_modrm_rm(struct insn *insn, struct pt_regs *regs)
+{
+ return get_reg_offset(insn, regs, REG_TYPE_RM);
+}
+
+/**
+ * insn_get_reg_offset_sib_base - Obtain register in base part of SiB byte
+ * @insn: Instruction structure containing the SiB byte
+ * @regs: Set of registers indicated by the SiB byte
+ *
+ * Obtain the register indicated by the base part of the SiB byte. The
+ * register is obtained as an offset from the base of pt_regs. In specific
+ * cases, the returned value can be -EDOM to indicate that the particular value
+ * of SiB does not refer to a register.
+ *
+ * Return: Register indicated by SiB's base, as an offset within struct pt_regs
+ */
+int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs)
+{
+ return get_reg_offset(insn, regs, REG_TYPE_BASE);
+}
+
+/**
+ * insn_get_reg_offset_sib_index - Obtain register in index part of SiB byte
+ * @insn: Instruction structure containing the SiB byte
+ * @regs: Set of registers indicated by the SiB byte
+ *
+ * Obtain the register indicated by the index part of the SiB byte. The
+ * register is obtained as an offset from the index of pt_regs. In specific
+ * cases, the returned value can be -EDOM to indicate that the particular value
+ * of SiB does not refer to a register.
+ *
+ * Return: Register indicated by SiB's base, as an offset within struct pt_regs
+ */
+int insn_get_reg_offset_sib_index(struct insn *insn, struct pt_regs *regs)
+{
+ return get_reg_offset(insn, regs, REG_TYPE_INDEX);
+}
+
/*
* return the address being referenced be instruction
* for rm=3 returning the content of the rm reg
--
2.9.3
Certain user space programs that run on virtual-8086 mode may utilize
instructions protected by the User-Mode Instruction Prevention (UMIP)
security feature present in new Intel processors: SGDT, SIDT and SMSW. In
such a case, a general protection fault is issued if UMIP is enabled. When
such a fault happens, the kernel catches it and emulates the results of
these instructions with dummy values. The purpose of this new
test is to verify whether the impacted instructions can be executed without
causing such #GP. If no #GP exceptions occur, we expect to exit virtual-
8086 mode from INT 0x80.
The instructions protected by UMIP are executed in representative use
cases:
a) the memory address of the result is given in the form of a displacement
from the base of the data segment
b) the memory address of the result is given in a general purpose register
c) the result is stored directly in a general purpose register.
Unfortunately, it is not possible to check the results against a set of
expected values because no emulation will occur in systems that do not have
the UMIP feature. Instead, results are printed for verification.
Cc: Andy Lutomirski <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Chen Yucong <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Fenghua Yu <[email protected]>
Cc: Huang Rui <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Ricardo Neri <[email protected]>
---
tools/testing/selftests/x86/entry_from_vm86.c | 39 ++++++++++++++++++++++++++-
1 file changed, 38 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/x86/entry_from_vm86.c b/tools/testing/selftests/x86/entry_from_vm86.c
index d075ea0..377b773 100644
--- a/tools/testing/selftests/x86/entry_from_vm86.c
+++ b/tools/testing/selftests/x86/entry_from_vm86.c
@@ -95,6 +95,22 @@ asm (
"int3\n\t"
"vmcode_int80:\n\t"
"int $0x80\n\t"
+ "umip:\n\t"
+ /* addressing via displacements */
+ "smsw (2052)\n\t"
+ "sidt (2054)\n\t"
+ "sgdt (2060)\n\t"
+ /* addressing via registers */
+ "mov $2066, %bx\n\t"
+ "smsw (%bx)\n\t"
+ "mov $2068, %bx\n\t"
+ "sidt (%bx)\n\t"
+ "mov $2074, %bx\n\t"
+ "sgdt (%bx)\n\t"
+ /* register operands, only for smsw */
+ "smsw %ax\n\t"
+ "mov %ax, (2080)\n\t"
+ "int $0x80\n\t"
".size vmcode, . - vmcode\n\t"
"end_vmcode:\n\t"
".code32\n\t"
@@ -103,7 +119,7 @@ asm (
extern unsigned char vmcode[], end_vmcode[];
extern unsigned char vmcode_bound[], vmcode_sysenter[], vmcode_syscall[],
- vmcode_sti[], vmcode_int3[], vmcode_int80[];
+ vmcode_sti[], vmcode_int3[], vmcode_int80[], umip[];
/* Returns false if the test was skipped. */
static bool do_test(struct vm86plus_struct *v86, unsigned long eip,
@@ -218,6 +234,27 @@ int main(void)
v86.regs.eax = (unsigned int)-1;
do_test(&v86, vmcode_int80 - vmcode, VM86_INTx, 0x80, "int80");
+ /* UMIP -- should exit with INTx 0x80 unless UMIP was not disabled */
+ do_test(&v86, umip - vmcode, VM86_INTx, 0x80, "UMIP tests");
+ printf("[INFO]\tResults of UMIP-protected instructions via displacements:\n");
+ printf("[INFO]\tSMSW:[0x%04x]\n", *(unsigned short *)(addr + 2052));
+ printf("[INFO]\tSIDT: limit[0x%04x]base[0x%08lx]\n",
+ *(unsigned short *)(addr + 2054),
+ *(unsigned long *)(addr + 2056));
+ printf("[INFO]\tSGDT: limit[0x%04x]base[0x%08lx]\n",
+ *(unsigned short *)(addr + 2060),
+ *(unsigned long *)(addr + 2062));
+ printf("[INFO]\tResults of UMIP-protected instructions via addressing in registers:\n");
+ printf("[INFO]\tSMSW:[0x%04x]\n", *(unsigned short *)(addr + 2066));
+ printf("[INFO]\tSIDT: limit[0x%04x]base[0x%08lx]\n",
+ *(unsigned short *)(addr + 2068),
+ *(unsigned long *)(addr + 2070));
+ printf("[INFO]\tSGDT: limit[0x%04x]base[0x%08lx]\n",
+ *(unsigned short *)(addr + 2074),
+ *(unsigned long *)(addr + 2076));
+ printf("[INFO]\tResults of SMSW via register operands:\n");
+ printf("[INFO]\tSMSW:[0x%04x]\n", *(unsigned short *)(addr + 2080));
+
/* Execute a null pointer */
v86.regs.cs = 0;
v86.regs.ss = 0;
--
2.9.3
If the User-Mode Instruction Prevention CPU feature is available and
enabled, a general protection fault will be issued if the instructions
sgdt, sldt, sidt, str or smsw are executed from user-mode context
(CPL > 0). If the fault was caused by any of the instructions protected
by UMIP, fixup_umip_exception will emulate dummy results for these
instructions. If emulation is successful, the result is passed to the
user space program and no SIGSEGV signal is emitted.
Please note that fixup_umip_exception also caters for the case when
the fault originated while running in virtual-8086 mode.
Cc: Andy Lutomirski <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Chen Yucong <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Fenghua Yu <[email protected]>
Cc: Huang Rui <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Liang Z. Li <[email protected]>
Cc: Alexandre Julliard <[email protected]>
Cc: Stas Sergeev <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/kernel/traps.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 948443e..86efbcb 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -65,6 +65,7 @@
#include <asm/trace/mpx.h>
#include <asm/mpx.h>
#include <asm/vm86.h>
+#include <asm/umip.h>
#ifdef CONFIG_X86_64
#include <asm/x86_init.h>
@@ -492,6 +493,9 @@ do_general_protection(struct pt_regs *regs, long error_code)
RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
cond_local_irq_enable(regs);
+ if (user_mode(regs) && fixup_umip_exception(regs))
+ return;
+
if (v8086_mode(regs)) {
local_irq_enable();
handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code);
--
2.9.3
fixup_umip_exception will be called from do_general_protection. If the
former returns false, the latter will issue a SIGSEGV with SEND_SIG_PRIV.
However, when emulation is successful but the emulated result cannot be
copied to user space memory, it is more accurate to issue a SIGSEGV with
SEGV_MAPERR with the offending address. A new function is inspired in
force_sig_info_fault is introduced to model the page fault.
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/kernel/umip.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 43 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index e932f40..5b6a7cf 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -170,6 +170,41 @@ static int __emulate_umip_insn(struct insn *insn, enum umip_insn umip_inst,
}
/**
+ * __force_sig_info_umip_fault - Force a SIGSEGV with SEGV_MAPERR
+ * @address: Address that caused the signal
+ * @regs: Register set containing the instruction pointer
+ *
+ * Force a SIGSEGV signal with SEGV_MAPERR as the error code. This function is
+ * intended to be used to provide a segmentation fault when the result of the
+ * UMIP emulation could not be copied to the user space memory.
+ *
+ * Return: none
+ */
+static void __force_sig_info_umip_fault(void __user *address,
+ struct pt_regs *regs)
+{
+ siginfo_t info;
+ struct task_struct *tsk = current;
+
+ if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV)) {
+ printk_ratelimited("%s[%d] umip emulation segfault ip:%lx sp:%lx error:%lx in %lx\n",
+ tsk->comm, task_pid_nr(tsk), regs->ip,
+ regs->sp, UMIP_PF_USER | UMIP_PF_WRITE,
+ regs->ip);
+ }
+
+ tsk->thread.cr2 = (unsigned long)address;
+ tsk->thread.error_code = UMIP_PF_USER | UMIP_PF_WRITE;
+ tsk->thread.trap_nr = X86_TRAP_PF;
+
+ info.si_signo = SIGSEGV;
+ info.si_errno = 0;
+ info.si_code = SEGV_MAPERR;
+ info.si_addr = address;
+ force_sig_info(SIGSEGV, &info, tsk);
+}
+
+/**
* fixup_umip_exception - Fixup #GP faults caused by UMIP
* @regs: Registers as saved when entering the #GP trap
*
@@ -254,8 +289,14 @@ bool fixup_umip_exception(struct pt_regs *regs)
} else {
uaddr = insn_get_addr_ref(&insn, regs);
nr_copied = copy_to_user(uaddr, dummy_data, dummy_data_size);
- if (nr_copied > 0)
- return false;
+ if (nr_copied > 0) {
+ /*
+ * If copy fails, send a signal and tell caller that
+ * fault was fixed up
+ */
+ __force_sig_info_umip_fault(uaddr, regs);
+ return true;
+ }
}
/* increase IP to let the program keep going */
--
2.9.3
The feature User-Mode Instruction Prevention present in recent Intel
processor prevents a group of instructions from being executed with
CPL > 0. Otherwise, a general protection fault is issued.
Rather than relaying this fault to the user space (in the form of a SIGSEGV
signal), the instructions protected by UMIP can be emulated to provide
dummy results. This allows to conserve the current kernel behavior and not
reveal the system resources that UMIP intends to protect (the global
descriptor and interrupt descriptor tables, the segment selectors of the
local descriptor table and the task state and the machine status word).
This emulation is needed because certain applications (e.g., WineHQ) rely
on this subset of instructions to function.
The instructions protected by UMIP can be split in two groups. Those who
return a kernel memory address (sgdt and sidt) and those who return a
value (sldt, str and smsw).
For the instructions that return a kernel memory address, applications
such as WineHQ rely on the result being located in the kernel memory space.
The result is emulated as a hard-coded value that, lies close to the top
of the kernel memory. The limit for the GDT and the IDT are set to zero.
The instructions sldt and str return a segment selector relative to the
base address of the global descriptor table. Since the actual address of
such table is not revealed, it makes sense to emulate the result as zero.
The instruction smsw is emulated to return the value that the register CR0
has at boot time as set in the head_32.
Care is taken to appropriately emulate the results when segmentation is
used. This is, rather than relying on USER_DS and USER_CS, the function
insn_get_addr_ref inspects the segment descriptor pointed by the registers
in pt_regs. This ensures that we correctly obtain the segment base address
and the address and operand sizes even if the user space application uses
local descriptor table.
Cc: Andy Lutomirski <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Chen Yucong <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Fenghua Yu <[email protected]>
Cc: Huang Rui <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Liang Z. Li <[email protected]>
Cc: Alexandre Julliard <[email protected]>
Cc: Stas Sergeev <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/include/asm/umip.h | 15 +++
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/umip.c | 264 ++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 280 insertions(+)
create mode 100644 arch/x86/include/asm/umip.h
create mode 100644 arch/x86/kernel/umip.c
diff --git a/arch/x86/include/asm/umip.h b/arch/x86/include/asm/umip.h
new file mode 100644
index 0000000..077b236
--- /dev/null
+++ b/arch/x86/include/asm/umip.h
@@ -0,0 +1,15 @@
+#ifndef _ASM_X86_UMIP_H
+#define _ASM_X86_UMIP_H
+
+#include <linux/types.h>
+#include <asm/ptrace.h>
+
+#ifdef CONFIG_X86_INTEL_UMIP
+bool fixup_umip_exception(struct pt_regs *regs);
+#else
+static inline bool fixup_umip_exception(struct pt_regs *regs)
+{
+ return false;
+}
+#endif /* CONFIG_X86_INTEL_UMIP */
+#endif /* _ASM_X86_UMIP_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 84c0059..0ded7b1 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -122,6 +122,7 @@ obj-$(CONFIG_EFI) += sysfb_efi.o
obj-$(CONFIG_PERF_EVENTS) += perf_regs.o
obj-$(CONFIG_TRACING) += tracepoint.o
obj-$(CONFIG_SCHED_MC_PRIO) += itmt.o
+obj-$(CONFIG_X86_INTEL_UMIP) += umip.o
ifdef CONFIG_FRAME_POINTER
obj-y += unwind_frame.o
diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
new file mode 100644
index 0000000..e932f40
--- /dev/null
+++ b/arch/x86/kernel/umip.c
@@ -0,0 +1,264 @@
+/*
+ * umip.c Emulation for instruction protected by the Intel User-Mode
+ * Instruction Prevention. The instructions are:
+ * sgdt
+ * sldt
+ * sidt
+ * str
+ * smsw
+ *
+ * Copyright (c) 2017, Intel Corporation.
+ * Ricardo Neri <[email protected]>
+ */
+
+#include <linux/uaccess.h>
+#include <asm/umip.h>
+#include <asm/traps.h>
+#include <asm/insn.h>
+#include <asm/insn-eval.h>
+#include <linux/ratelimit.h>
+
+/*
+ * == Base addresses of GDT and IDT
+ * Some applications to function rely finding the global descriptor table (GDT)
+ * and the interrupt descriptor table (IDT) in kernel memory.
+ * For x86_32, the selected values do not match any particular hole, but it
+ * suffices to provide a memory location within kernel memory.
+ *
+ * == CRO flags for SMSW
+ * Use the flags given when booting, as found in head_32.S
+ */
+
+#define CR0_STATE (X86_CR0_PE | X86_CR0_MP | X86_CR0_ET | X86_CR0_NE | \
+ X86_CR0_WP | X86_CR0_AM)
+#define UMIP_DUMMY_GDT_BASE 0xfffe0000
+#define UMIP_DUMMY_IDT_BASE 0xffff0000
+
+/*
+ * Definitions for x86 page fault error code bits. Only a simple
+ * pagefault during a write in user context is supported.
+ */
+#define UMIP_PF_USER BIT(2)
+#define UMIP_PF_WRITE BIT(1)
+
+enum umip_insn {
+ UMIP_SGDT = 0, /* opcode 0f 01 ModR/M reg 0 */
+ UMIP_SIDT, /* opcode 0f 01 ModR/M reg 1 */
+ UMIP_SLDT, /* opcode 0f 00 ModR/M reg 0 */
+ UMIP_SMSW, /* opcode 0f 01 ModR/M reg 4 */
+ UMIP_STR, /* opcode 0f 00 ModR/M reg 1 */
+};
+
+/**
+ * __identify_insn - Identify a UMIP-protected instruction
+ * @insn: Instruction structure with opcode and ModRM byte.
+ *
+ * From the instruction opcode and the reg part of the ModRM byte, identify,
+ * if any, a UMIP-protected instruction.
+ *
+ * Return: an enumeration of a UMIP-protected instruction; -EINVAL on failure.
+ */
+static int __identify_insn(struct insn *insn)
+{
+ /* By getting modrm we also get the opcode. */
+ insn_get_modrm(insn);
+
+ /* All the instructions of interest start with 0x0f. */
+ if (insn->opcode.bytes[0] != 0xf)
+ return -EINVAL;
+
+ if (insn->opcode.bytes[1] == 0x1) {
+ switch (X86_MODRM_REG(insn->modrm.value)) {
+ case 0:
+ return UMIP_SGDT;
+ case 1:
+ return UMIP_SIDT;
+ case 4:
+ return UMIP_SMSW;
+ default:
+ return -EINVAL;
+ }
+ } else if (insn->opcode.bytes[1] == 0x0) {
+ if (X86_MODRM_REG(insn->modrm.value) == 0)
+ return UMIP_SLDT;
+ else if (X86_MODRM_REG(insn->modrm.value) == 1)
+ return UMIP_STR;
+ else
+ return -EINVAL;
+ } else {
+ return -EINVAL;
+ }
+}
+
+/**
+ * __emulate_umip_insn - Emulate UMIP instructions with dummy values
+ * @insn: Instruction structure with ModRM byte
+ * @umip_inst: Instruction to emulate
+ * @data: Buffer onto which the dummy values will be copied
+ * @data_size: Size of the emulated result
+ *
+ * Emulate an instruction protected by UMIP. The result of the emulation
+ * is saved in the provided buffer. The size of the results depends on both
+ * the instruction and type of operand (register vs memory address). Thus,
+ * the size of the result needs to be updated.
+ *
+ * Result: 0 if success, -EINVAL on failure to emulate
+ */
+static int __emulate_umip_insn(struct insn *insn, enum umip_insn umip_inst,
+ unsigned char *data, int *data_size)
+{
+ unsigned long dummy_base_addr;
+ unsigned short dummy_limit = 0;
+ unsigned int dummy_value = 0;
+
+ switch (umip_inst) {
+ /*
+ * These two instructions return the base address and limit of the
+ * global and interrupt descriptor table. The base address can be
+ * 24-bit, 32-bit or 64-bit. Limit is always 16-bit. If the operand
+ * size is 16-bit the returned value of the base address is supposed
+ * to be a zero-extended 24-byte number. However, it seems that a
+ * 32-byte number is always returned in legacy protected mode
+ * irrespective of the operand size.
+ */
+ case UMIP_SGDT:
+ /* fall through */
+ case UMIP_SIDT:
+ if (umip_inst == UMIP_SGDT)
+ dummy_base_addr = UMIP_DUMMY_GDT_BASE;
+ else
+ dummy_base_addr = UMIP_DUMMY_IDT_BASE;
+ if (X86_MODRM_MOD(insn->modrm.value) == 3) {
+ /* SGDT and SIDT do not take register as argument. */
+ return -EINVAL;
+ }
+
+ memcpy(data + 2, &dummy_base_addr, sizeof(dummy_base_addr));
+ memcpy(data, &dummy_limit, sizeof(dummy_limit));
+ *data_size = sizeof(dummy_base_addr) + sizeof(dummy_limit);
+ break;
+ case UMIP_SMSW:
+ /*
+ * Even though CR0_STATE contain 4 bytes, the number
+ * of bytes to be copied in the result buffer is determined
+ * by whether the operand is a register or a memory location.
+ */
+ dummy_value = CR0_STATE;
+ /*
+ * These two instructions return a 16-bit value. We return
+ * all zeros. This is equivalent to a null descriptor for
+ * str and sldt.
+ */
+ /* fall through */
+ case UMIP_SLDT:
+ /* fall through */
+ case UMIP_STR:
+ /* if operand is a register, it is zero-extended */
+ if (X86_MODRM_MOD(insn->modrm.value) == 3) {
+ memset(data, 0, insn->opnd_bytes);
+ *data_size = insn->opnd_bytes;
+ /* if not, only the two least significant bytes are copied */
+ } else {
+ *data_size = 2;
+ }
+ memcpy(data, &dummy_value, sizeof(dummy_value));
+ break;
+ default:
+ return -EINVAL;
+ }
+ return 0;
+}
+
+/**
+ * fixup_umip_exception - Fixup #GP faults caused by UMIP
+ * @regs: Registers as saved when entering the #GP trap
+ *
+ * The instructions sgdt, sidt, str, smsw, sldt cause a general protection
+ * fault if with CPL > 0 (i.e., from user space). This function can be
+ * used to emulate the results of the aforementioned instructions with
+ * dummy values. Results are copied to user-space memory as indicated by
+ * the instruction pointed by EIP using the registers indicated in the
+ * instruction operands. This function also takes care of determining
+ * the address to which the results must be copied.
+ */
+bool fixup_umip_exception(struct pt_regs *regs)
+{
+ struct insn insn;
+ unsigned char buf[MAX_INSN_SIZE];
+ /* 10 bytes is the maximum size of the result of UMIP instructions */
+ unsigned char dummy_data[10] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+ unsigned long seg_base;
+ int not_copied, nr_copied, reg_offset, dummy_data_size;
+ void __user *uaddr;
+ unsigned long *reg_addr;
+ enum umip_insn umip_inst;
+
+ /*
+ * Use the segment base in case user space used a different code
+ * segment, either in protected (e.g., from an LDT) or virtual-8086
+ * modes. In most of the cases seg_base will be zero as in USER_CS.
+ */
+ seg_base = insn_get_seg_base(regs, &insn, offsetof(struct pt_regs, ip),
+ true);
+ not_copied = copy_from_user(buf, (void __user *)(seg_base + regs->ip),
+ sizeof(buf));
+ nr_copied = sizeof(buf) - not_copied;
+ /*
+ * The copy_from_user above could have failed if user code is protected
+ * by a memory protection key. Give up on emulation in such a case.
+ * Should we issue a page fault?
+ */
+ if (!nr_copied)
+ return false;
+
+ insn_init(&insn, buf, nr_copied, 0);
+
+ /*
+ * Override the default operand and address sizes to what is specified
+ * in the code segment descriptor. The instruction decoder only sets
+ * the address size it to either 4 or 8 address bytes and does nothing
+ * for the operand bytes. This OK for most of the cases, but we could
+ * have special cases where, for instance, a 16-bit code segment
+ * descriptor is used.
+ * If there are overrides, the instruction decoder correctly updates
+ * these values, even for 16-bit defaults.
+ */
+ insn.addr_bytes = insn_get_seg_default_address_bytes(regs);
+ insn.opnd_bytes = insn_get_seg_default_operand_bytes(regs);
+
+ if (!insn.addr_bytes || !insn.opnd_bytes)
+ return false;
+
+#ifdef CONFIG_X86_64
+ if (user_64bit_mode(regs))
+ return false;
+#endif
+
+ insn_get_length(&insn);
+ if (nr_copied < insn.length)
+ return false;
+
+ umip_inst = __identify_insn(&insn);
+ /* Check if we found an instruction protected by UMIP */
+ if (umip_inst < 0)
+ return false;
+
+ if (__emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size))
+ return false;
+
+ /* If operand is a register, write directly to it */
+ if (X86_MODRM_MOD(insn.modrm.value) == 3) {
+ reg_offset = insn_get_reg_offset_modrm_rm(&insn, regs);
+ reg_addr = (unsigned long *)((unsigned long)regs + reg_offset);
+ memcpy(reg_addr, dummy_data, dummy_data_size);
+ } else {
+ uaddr = insn_get_addr_ref(&insn, regs);
+ nr_copied = copy_to_user(uaddr, dummy_data, dummy_data_size);
+ if (nr_copied > 0)
+ return false;
+ }
+
+ /* increase IP to let the program keep going */
+ regs->ip += insn.length;
+ return true;
+}
--
2.9.3
The 32-bit and 64-bit address encodings are identical. This means that we
can use the same function in both cases. In order to reuse the function for
32-bit address encodings, we must sign-extend our 32-bit signed operands to
64-bit signed variables (only for 64-bit builds). To decide on whether sign
extension is needed, we rely on the address size as given by the
instruction structure.
Lastly, before computing the linear address, we must truncate our signed
64-bit signed effective address if the address size is 32-bit.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Thomas Garnier <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/lib/insn-eval.c | 44 ++++++++++++++++++++++++++++++++------------
1 file changed, 32 insertions(+), 12 deletions(-)
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index edb360f..a9a1704 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -559,6 +559,15 @@ int insn_get_reg_offset_sib_index(struct insn *insn, struct pt_regs *regs)
return get_reg_offset(insn, regs, REG_TYPE_INDEX);
}
+static inline long __to_signed_long(unsigned long val, int long_bytes)
+{
+#ifdef CONFIG_X86_64
+ return long_bytes == 4 ? (long)((int)((val) & 0xffffffff)) : (long)val;
+#else
+ return (long)val;
+#endif
+}
+
/*
* return the address being referenced be instruction
* for rm=3 returning the content of the rm reg
@@ -567,19 +576,21 @@ int insn_get_reg_offset_sib_index(struct insn *insn, struct pt_regs *regs)
void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
{
unsigned long linear_addr, seg_base_addr;
- long eff_addr, base, indx;
- int addr_offset, base_offset, indx_offset;
+ long eff_addr, base, indx, tmp;
+ int addr_offset, base_offset, indx_offset, addr_bytes;
insn_byte_t sib;
insn_get_modrm(insn);
insn_get_sib(insn);
sib = insn->sib.value;
+ addr_bytes = insn->addr_bytes;
if (X86_MODRM_MOD(insn->modrm.value) == 3) {
addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
if (addr_offset < 0)
goto out_err;
- eff_addr = regs_get_register(regs, addr_offset);
+ tmp = regs_get_register(regs, addr_offset);
+ eff_addr = __to_signed_long(tmp, addr_bytes);
seg_base_addr = insn_get_seg_base(regs, insn, addr_offset,
false);
} else {
@@ -591,20 +602,24 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
* in the address computation.
*/
base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
- if (unlikely(base_offset == -EDOM))
+ if (unlikely(base_offset == -EDOM)) {
base = 0;
- else if (unlikely(base_offset < 0))
+ } else if (unlikely(base_offset < 0)) {
goto out_err;
- else
- base = regs_get_register(regs, base_offset);
+ } else {
+ tmp = regs_get_register(regs, base_offset);
+ base = __to_signed_long(tmp, addr_bytes);
+ }
indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
- if (unlikely(indx_offset == -EDOM))
+ if (unlikely(indx_offset == -EDOM)) {
indx = 0;
- else if (unlikely(indx_offset < 0))
+ } else if (unlikely(indx_offset < 0)) {
goto out_err;
- else
- indx = regs_get_register(regs, indx_offset);
+ } else {
+ tmp = regs_get_register(regs, indx_offset);
+ indx = __to_signed_long(tmp, addr_bytes);
+ }
eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
seg_base_addr = insn_get_seg_base(regs, insn,
@@ -625,13 +640,18 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
} else if (addr_offset < 0) {
goto out_err;
} else {
- eff_addr = regs_get_register(regs, addr_offset);
+ tmp = regs_get_register(regs, addr_offset);
+ eff_addr = __to_signed_long(tmp, addr_bytes);
}
seg_base_addr = insn_get_seg_base(regs, insn,
addr_offset, false);
}
eff_addr += insn->displacement.value;
}
+ /* truncate to 4 bytes for 32-bit effective addresses */
+ if (addr_bytes == 4)
+ eff_addr &= 0xffffffff;
+
linear_addr = (unsigned long)eff_addr + seg_base_addr;
return (void __user *)linear_addr;
--
2.9.3
Tasks running in virtual-8086 mode or in protected mode with code
segment descriptors that specify 16-bit default address sizes via the
D bit will use 16-bit addressing form encodings as described in the Intel
64 and IA-32 Architecture Software Developer's Manual Volume 2A Section
2.1.5. 16-bit addressing encodings differ in several ways from the
32-bit/64-bit addressing form encodings: the r/m part of the ModRM byte
points to different registers and, in some cases, addresses can be
indicated by the addition of the value of two registers. Also, there is
no support for SiB bytes. Thus, a separate function is needed to parse
this form of addressing.
A couple of functions are introduced. get_reg_offset_16 obtains the
offset from the base of pt_regs of the registers indicated by the ModRM
byte of the address encoding. insn_get_addr_ref_16 computes the linear
address indicated by the instructions using the value of the registers
given by ModRM as well as the base address of the segment.
Lastly, the original function insn_get_addr_ref is renamed as
insn_get_addr_ref_32_64. A new insn_get_addr_ref function decides what
type of address decoding must be done base on the number of address bytes
given by the instruction. Documentation for insn_get_addr_ref_32_64 is
also improved.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Thomas Garnier <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/lib/insn-eval.c | 137 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 137 insertions(+)
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index a9a1704..cb1076d 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -306,6 +306,73 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
}
/**
+ * get_reg_offset_16 - Obtain offset of register indicated by instruction
+ * @insn: Instruction structure containing ModRM and SiB bytes
+ * @regs: Set of registers referred by the instruction
+ * @offs1: Offset of the first operand register
+ * @offs2: Offset of the second opeand register, if applicable.
+ *
+ * Obtain the offset, in pt_regs, of the registers indicated by the ModRM byte
+ * within insn. This function is to be used with 16-bit address encodings. The
+ * offs1 and offs2 will be written with the offset of the two registers
+ * indicated by the instruction. In cases where any of the registers is not
+ * referenced by the instruction, the value will be set to -EDOM.
+ *
+ * Return: 0 on success, -EINVAL on failure.
+ */
+static int get_reg_offset_16(struct insn *insn, struct pt_regs *regs,
+ int *offs1, int *offs2)
+{
+ /* 16-bit addressing can use one or two registers */
+ static const int regoff1[] = {
+ offsetof(struct pt_regs, bx),
+ offsetof(struct pt_regs, bx),
+ offsetof(struct pt_regs, bp),
+ offsetof(struct pt_regs, bp),
+ offsetof(struct pt_regs, si),
+ offsetof(struct pt_regs, di),
+ offsetof(struct pt_regs, bp),
+ offsetof(struct pt_regs, bx),
+ };
+
+ static const int regoff2[] = {
+ offsetof(struct pt_regs, si),
+ offsetof(struct pt_regs, di),
+ offsetof(struct pt_regs, si),
+ offsetof(struct pt_regs, di),
+ -EDOM,
+ -EDOM,
+ -EDOM,
+ -EDOM,
+ };
+
+ if (!offs1 || !offs2)
+ return -EINVAL;
+
+ /* operand is a register, use the generic function */
+ if (X86_MODRM_MOD(insn->modrm.value) == 3) {
+ *offs1 = insn_get_reg_offset_modrm_rm(insn, regs);
+ *offs2 = -EDOM;
+ return 0;
+ }
+
+ *offs1 = regoff1[X86_MODRM_RM(insn->modrm.value)];
+ *offs2 = regoff2[X86_MODRM_RM(insn->modrm.value)];
+
+ /*
+ * If no displacement is indicated in the mod part of the ModRM byte,
+ * (mod part is 0) and the r/m part of the same byte is 6, no register
+ * is used caculate the operand address. An r/m part of 6 means that
+ * the second register offset is already invalid.
+ */
+ if ((X86_MODRM_MOD(insn->modrm.value) == 0) &&
+ (X86_MODRM_RM(insn->modrm.value) == 6))
+ *offs1 = -EDOM;
+
+ return 0;
+}
+
+/**
* get_desc() - Obtain address of segment descriptor
* @seg: Segment selector
* @desc: Pointer to the selected segment descriptor
@@ -559,6 +626,76 @@ int insn_get_reg_offset_sib_index(struct insn *insn, struct pt_regs *regs)
return get_reg_offset(insn, regs, REG_TYPE_INDEX);
}
+/**
+ * insn_get_addr_ref_16 - Obtain the 16-bit address referred by instruction
+ * @insn: Instruction structure containing ModRM byte and displacement
+ * @regs: Set of registers referred by the instruction
+ *
+ * This function is to be used with 16-bit address encodings. Obtain the memory
+ * address referred by the instruction's ModRM bytes and displacement. Also, the
+ * segment used as base is determined by either any segment override prefixes in
+ * insn or the default segment of the registers involved in the address
+ * computation.
+ * the ModRM byte
+ *
+ * Return: linear address referenced by instruction and registers
+ */
+static void __user *insn_get_addr_ref_16(struct insn *insn,
+ struct pt_regs *regs)
+{
+ unsigned long linear_addr, seg_base_addr;
+ short eff_addr, addr1 = 0, addr2 = 0;
+ int addr_offset1, addr_offset2;
+ int ret;
+
+ insn_get_modrm(insn);
+ insn_get_displacement(insn);
+
+ /*
+ * If operand is a register, the layout is the same as in
+ * 32-bit and 64-bit addressing.
+ */
+ if (X86_MODRM_MOD(insn->modrm.value) == 3) {
+ addr_offset1 = get_reg_offset(insn, regs, REG_TYPE_RM);
+ if (addr_offset1 < 0)
+ goto out_err;
+ eff_addr = regs_get_register(regs, addr_offset1);
+ seg_base_addr = insn_get_seg_base(regs, insn, addr_offset1,
+ false);
+ } else {
+ ret = get_reg_offset_16(insn, regs, &addr_offset1,
+ &addr_offset2);
+ if (ret < 0)
+ goto out_err;
+ /*
+ * Don't fail on invalid offset values. They might be invalid
+ * because they cannot be used for this particular value of
+ * the ModRM. Instead, use them in the computation only if
+ * they contain a valid value.
+ */
+ if (addr_offset1 != -EDOM)
+ addr1 = 0xffff & regs_get_register(regs, addr_offset1);
+ if (addr_offset2 != -EDOM)
+ addr2 = 0xffff & regs_get_register(regs, addr_offset2);
+ eff_addr = addr1 + addr2;
+ /*
+ * The first register is in the operand implies the SS or DS
+ * segment selectors, the second register in the operand can
+ * only imply DS. Thus, use the first register to obtain
+ * the segment selector.
+ */
+ seg_base_addr = insn_get_seg_base(regs, insn, addr_offset1,
+ false);
+
+ eff_addr += (insn->displacement.value & 0xffff);
+ }
+ linear_addr = (unsigned short)eff_addr + seg_base_addr;
+
+ return (void __user *)linear_addr;
+out_err:
+ return (void __user *)-1;
+}
+
static inline long __to_signed_long(unsigned long val, int long_bytes)
{
#ifdef CONFIG_X86_64
--
2.9.3
Convert the function insn_get_add_ref into a wrapper function that calls
the correct static address-decoding function depending on the size of the
address. In this way, callers do not need to worry about calling the
correct function and decreases the number of functions that need to be
exposed.
To this end, the original 32/64-bit insn_get_addr_ref is renamed as
insn_get_addr_ref_32_64 to reflect the type of address encodings that it
handles.
Documentation is added to the new wrapper function and the documentation
for the 32/64-bit address decoding function is improved.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Thomas Garnier <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/lib/insn-eval.c | 45 ++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 40 insertions(+), 5 deletions(-)
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index cb1076d..e633588 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -705,12 +705,21 @@ static inline long __to_signed_long(unsigned long val, int long_bytes)
#endif
}
-/*
- * return the address being referenced be instruction
- * for rm=3 returning the content of the rm reg
- * for rm!=3 calculates the address using SIB and Disp
+/**
+ * insn_get_addr_ref_32_64 - Obtain a 32/64-bit address referred by instruction
+ * @insn: Instruction struct with ModRM and SiB bytes and displacement
+ * @regs: Set of registers referred by the instruction
+ *
+ * This function is to be used with 32-bit and 64-bit address encodings. Obtain
+ * the memory address referred by the instruction's ModRM bytes and
+ * displacement. Also, the segment used as base is determined by either any
+ * segment override prefixes in insn or the default segment of the registers
+ * involved in the linear address computation.
+ *
+ * Return: linear address referenced by instruction and registers
*/
-void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
+static void __user *insn_get_addr_ref_32_64(struct insn *insn,
+ struct pt_regs *regs)
{
unsigned long linear_addr, seg_base_addr;
long eff_addr, base, indx, tmp;
@@ -795,3 +804,29 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
out_err:
return (void __user *)-1;
}
+
+/**
+ * insn_get_addr_ref - Obtain the linear address referred by instruction
+ * @insn: Instruction structure containing ModRM byte and displacement
+ * @regs: Set of registers referred by the instruction
+ *
+ * Obtain the memory address referred by the instruction's ModRM bytes and
+ * displacement. Also, the segment used as base is determined by either any
+ * segment override prefixes in insn or the default segment of the registers
+ * involved in the address computation.
+ *
+ * Return: linear address referenced by instruction and registers
+ */
+void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
+{
+ switch (insn->addr_bytes) {
+ case 2:
+ return insn_get_addr_ref_16(insn, regs);
+ case 4:
+ /* fall through */
+ case 8:
+ return insn_get_addr_ref_32_64(insn, regs);
+ default:
+ return (void __user *)-1;
+ }
+}
--
2.9.3
User-Mode Instruction Prevention is a security feature present in new
Intel processors that, when set, prevents the execution of a subset of
instructions if such instructions are executed in user mode (CPL > 0).
Attempting to execute such instructions causes a general protection
exception.
The subset of instructions comprises:
* SGDT - Store Global Descriptor Table
* SIDT - Store Interrupt Descriptor Table
* SLDT - Store Local Descriptor Table
* SMSW - Store Machine Status Word
* STR - Store Task Register
This feature is also added to the list of disabled-features to allow
a cleaner handling of build-time configuration.
Cc: Andy Lutomirski <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Chen Yucong <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Fenghua Yu <[email protected]>
Cc: Huang Rui <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Liang Z. Li <[email protected]>
Cc: Alexandre Julliard <[email protected]>
Cc: Stas Sergeev <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/disabled-features.h | 8 +++++++-
arch/x86/include/uapi/asm/processor-flags.h | 2 ++
3 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 4e77723..0739f1e 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -286,6 +286,7 @@
/* Intel-defined CPU features, CPUID level 0x00000007:0 (ecx), word 16 */
#define X86_FEATURE_AVX512VBMI (16*32+ 1) /* AVX512 Vector Bit Manipulation instructions*/
+#define X86_FEATURE_UMIP (16*32+ 2) /* User Mode Instruction Protection */
#define X86_FEATURE_PKU (16*32+ 3) /* Protection Keys for Userspace */
#define X86_FEATURE_OSPKE (16*32+ 4) /* OS Protection Keys Enable */
#define X86_FEATURE_AVX512_VPOPCNTDQ (16*32+14) /* POPCNT for vectors of DW/QW */
diff --git a/arch/x86/include/asm/disabled-features.h b/arch/x86/include/asm/disabled-features.h
index 85599ad..4707445 100644
--- a/arch/x86/include/asm/disabled-features.h
+++ b/arch/x86/include/asm/disabled-features.h
@@ -16,6 +16,12 @@
# define DISABLE_MPX (1<<(X86_FEATURE_MPX & 31))
#endif
+#ifdef CONFIG_X86_INTEL_UMIP
+# define DISABLE_UMIP 0
+#else
+# define DISABLE_UMIP (1<<(X86_FEATURE_UMIP & 31))
+#endif
+
#ifdef CONFIG_X86_64
# define DISABLE_VME (1<<(X86_FEATURE_VME & 31))
# define DISABLE_K6_MTRR (1<<(X86_FEATURE_K6_MTRR & 31))
@@ -55,7 +61,7 @@
#define DISABLED_MASK13 0
#define DISABLED_MASK14 0
#define DISABLED_MASK15 0
-#define DISABLED_MASK16 (DISABLE_PKU|DISABLE_OSPKE)
+#define DISABLED_MASK16 (DISABLE_PKU|DISABLE_OSPKE|DISABLE_UMIP)
#define DISABLED_MASK17 0
#define DISABLED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 18)
diff --git a/arch/x86/include/uapi/asm/processor-flags.h b/arch/x86/include/uapi/asm/processor-flags.h
index 567de50..d2c2af8 100644
--- a/arch/x86/include/uapi/asm/processor-flags.h
+++ b/arch/x86/include/uapi/asm/processor-flags.h
@@ -104,6 +104,8 @@
#define X86_CR4_OSFXSR _BITUL(X86_CR4_OSFXSR_BIT)
#define X86_CR4_OSXMMEXCPT_BIT 10 /* enable unmasked SSE exceptions */
#define X86_CR4_OSXMMEXCPT _BITUL(X86_CR4_OSXMMEXCPT_BIT)
+#define X86_CR4_UMIP_BIT 11 /* enable UMIP support */
+#define X86_CR4_UMIP _BITUL(X86_CR4_UMIP_BIT)
#define X86_CR4_VMXE_BIT 13 /* enable VMX virtualization */
#define X86_CR4_VMXE _BITUL(X86_CR4_VMXE_BIT)
#define X86_CR4_SMXE_BIT 14 /* enable safer mode (TXT) */
--
2.9.3
Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software
Developer's Manual volume 2A states that when a SIB byte is used and the
base of the SIB byte points to R/EBP (i.e., base = 5) and the mod part
of the ModRM byte is zero, the value of such register will not be used
as part of the address computation. To signal this, a -EDOM error is
returned to indicate callers that they should ignore the value.
Also, for this particular case, a displacement of 32-bits should follow
the SIB byte if the mod part of ModRM is equal to zero. The instruction
decoder ensures that this is the case.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Nathan Howard <[email protected]>
Cc: Adan Hawthorn <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/mm/mpx.c | 29 ++++++++++++++++++++++-------
1 file changed, 22 insertions(+), 7 deletions(-)
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index d9e92d6..ef7eb67 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -121,6 +121,17 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
case REG_TYPE_BASE:
regno = X86_SIB_BASE(insn->sib.value);
+ /*
+ * If mod is 0 and register R/EBP (regno=5) is indicated in the
+ * base part of the SIB byte, the value of such register should
+ * not be used in the address computation. Also, a 32-bit
+ * displacement is expected in this case; the instruction
+ * decoder takes care of it. This is true for both R13 and
+ * R/EBP as REX.B will not be decoded.
+ */
+ if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0)
+ return -EDOM;
+
if (X86_REX_B(insn->rex_prefix.value))
regno += 8;
break;
@@ -161,16 +172,21 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
eff_addr = regs_get_register(regs, addr_offset);
} else {
if (insn->sib.nbytes) {
+ /*
+ * Negative values in the base and index offset means
+ * an error when decoding the SIB byte. Except -EDOM,
+ * which means that the registers should not be used
+ * in the address computation.
+ */
base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
- if (base_offset < 0)
+ if (unlikely(base_offset == -EDOM))
+ base = 0;
+ else if (unlikely(base_offset < 0))
goto out_err;
+ else
+ base = regs_get_register(regs, base_offset);
indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
- /*
- * A negative offset generally means a error, except
- * -EDOM, which means that the contents of the register
- * should not be used as index.
- */
if (unlikely(indx_offset == -EDOM))
indx = 0;
else if (unlikely(indx_offset < 0))
@@ -178,7 +194,6 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
else
indx = regs_get_register(regs, indx_offset);
- base = regs_get_register(regs, base_offset);
eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
} else {
addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
--
2.9.3
insn_get_addr_ref returns the effective address as defined by the
section 3.7.5.1 Vol 1 of the Intel 64 and IA-32 Architectures Software
Developer's Manual. In order to compute the linear address, we must add
to the effective address the segment base address as set in the segment
descriptor. Furthermore, the segment descriptor to use depends on the
register that is used as the base of the effective address. The effective
base address varies depending on whether the operand is a register or a
memory address and on whether a SiB byte is used.
In most cases, the segment base address will be 0 if the USER_DS/USER32_DS
segment is used or if segmentation is not used. However, the base address
is not necessarily zero if a user programs defines its own segments. This
is possible by using a local descriptor table.
Since the effective address is a signed quantity, the unsigned segment
base address saved in a separate variable and added to the final effective
address.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Thomas Garnier <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/lib/insn-eval.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index ea10b03..edb360f 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -566,7 +566,7 @@ int insn_get_reg_offset_sib_index(struct insn *insn, struct pt_regs *regs)
*/
void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
{
- unsigned long linear_addr;
+ unsigned long linear_addr, seg_base_addr;
long eff_addr, base, indx;
int addr_offset, base_offset, indx_offset;
insn_byte_t sib;
@@ -580,6 +580,8 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
if (addr_offset < 0)
goto out_err;
eff_addr = regs_get_register(regs, addr_offset);
+ seg_base_addr = insn_get_seg_base(regs, insn, addr_offset,
+ false);
} else {
if (insn->sib.nbytes) {
/*
@@ -605,6 +607,8 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
indx = regs_get_register(regs, indx_offset);
eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
+ seg_base_addr = insn_get_seg_base(regs, insn,
+ base_offset, false);
} else {
addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
/* -EDOM means that we must ignore the address_offset.
@@ -623,10 +627,12 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
} else {
eff_addr = regs_get_register(regs, addr_offset);
}
+ seg_base_addr = insn_get_seg_base(regs, insn,
+ addr_offset, false);
}
eff_addr += insn->displacement.value;
}
- linear_addr = (unsigned long)eff_addr;
+ linear_addr = (unsigned long)eff_addr + seg_base_addr;
return (void __user *)linear_addr;
out_err:
--
2.9.3
Section 2.2.1.3 of the Intel 64 and IA-32 Architectures Software
Developer's Manual volume 2A states that when the mod part of the ModRM
byte is zero and R/EBP is specified in the R/M part of such bit, the value
of the aforementioned register should not be used in the address
computation. Instead, a 32-bit displacement is expected. The instruction
decoder takes care of setting the displacement to the expected value.
Returning -EDOM signals callers that they should ignore the value of such
register when computing the address encoded in the instruction operands.
Also, callers should exercise care to correctly interpret this particular
case. In IA-32e 64-bit mode, the address is given by the displacement plus
the value of the RIP. In IA-32e compatibility mode, the value of EIP is
ignored. This correction is done for our insn_get_addr_ref.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Thomas Garnier <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/lib/insn-eval.c | 25 +++++++++++++++++++++++--
1 file changed, 23 insertions(+), 2 deletions(-)
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index cda6c71..ea10b03 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -250,6 +250,14 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
switch (type) {
case REG_TYPE_RM:
regno = X86_MODRM_RM(insn->modrm.value);
+ /* if mod=0, register R/EBP is not used in the address
+ * computation. Instead, a 32-bit displacement is expected;
+ * the instruction decoder takes care of reading such
+ * displacement. This is true for both R/EBP and R13, as the
+ * REX.B bit is not decoded.
+ */
+ if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0)
+ return -EDOM;
if (X86_REX_B(insn->rex_prefix.value))
regno += 8;
break;
@@ -599,9 +607,22 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
} else {
addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
- if (addr_offset < 0)
+ /* -EDOM means that we must ignore the address_offset.
+ * The only case in which we see this value is when
+ * R/M points to R/EBP. In such a case, in 64-bit mode
+ * the effective address is relative to tho RIP.
+ */
+ if (addr_offset == -EDOM) {
+ eff_addr = 0;
+#ifdef CONFIG_X86_64
+ if (user_64bit_mode(regs))
+ eff_addr = (long)regs->ip;
+#endif
+ } else if (addr_offset < 0) {
goto out_err;
- eff_addr = regs_get_register(regs, addr_offset);
+ } else {
+ eff_addr = regs_get_register(regs, addr_offset);
+ }
}
eff_addr += insn->displacement.value;
}
--
2.9.3
These functions read the default values of the address and operand sizes
as specified in the segment descriptor. This information is determined
from the D and L bits. Hence, it can be used for both IA-32e 64-bit and
32-bit legacy modes. For virtual-8086 mode, the default address and
operand sizes are always 2 bytes.
The D bit is only meaningful for code segments. Thus, these functions
always use the code segment selector contained in regs.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Thomas Garnier <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/include/asm/insn-eval.h | 2 +
arch/x86/lib/insn-eval.c | 80 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 82 insertions(+)
diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
index b201742..a0d81fc 100644
--- a/arch/x86/include/asm/insn-eval.h
+++ b/arch/x86/include/asm/insn-eval.h
@@ -15,6 +15,8 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs);
int insn_get_reg_offset_modrm_rm(struct insn *insn, struct pt_regs *regs);
int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs);
int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs);
+unsigned char insn_get_seg_default_address_bytes(struct pt_regs *regs);
+unsigned char insn_get_seg_default_operand_bytes(struct pt_regs *regs);
unsigned long insn_get_seg_base(struct pt_regs *regs, struct insn *insn,
int regoff, bool use_default_seg);
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 383ca83..cda6c71 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -421,6 +421,86 @@ unsigned long insn_get_seg_base(struct pt_regs *regs, struct insn *insn,
}
/**
+ * insn_get_seg_default_address_bytes - Obtain default address size of segment
+ * @regs: Set of registers containing the segment selector
+ *
+ * Obtain the default address size as indicated in the segment descriptor
+ * selected in regs' code segment selector. In protected mode, the default
+ * address is determined by inspecting the L and D bits of the segment
+ * descriptor. In virtual-8086 mode, the default is always two bytes.
+ *
+ * Return: Default address size of segment
+ */
+unsigned char insn_get_seg_default_address_bytes(struct pt_regs *regs)
+{
+ struct desc_struct *desc;
+ unsigned short seg;
+ int ret;
+
+ if (v8086_mode(regs))
+ return 2;
+
+ seg = (unsigned short)regs->cs;
+
+ ret = get_desc(seg, &desc);
+ if (ret)
+ return 0;
+
+ switch ((desc->l << 1) | desc->d) {
+ case 0: /* Legacy mode. 16-bit addresses. CS.L=0, CS.D=0 */
+ return 2;
+ case 1: /* Legacy mode. 32-bit addresses. CS.L=0, CS.D=1 */
+ return 4;
+ case 2: /* IA-32e 64-bit mode. 64-bit addresses. CS.L=1, CS.D=0 */
+ return 8;
+ case 3: /* Invalid setting. CS.L=1, CS.D=1 */
+ /* fall through */
+ default:
+ return 0;
+ }
+}
+
+/**
+ * insn_get_seg_default_operand_bytes - Obtain default operand size of segment
+ * @regs: Set of registers containing the segment selector
+ *
+ * Obtain the default operand size as indicated in the segment descriptor
+ * selected in regs' code segment selector. In protected mode, the default
+ * operand size is determined by inspecting the L and D bits of the segment
+ * descriptor. In virtual-8086 mode, the default is always two bytes.
+ *
+ * Return: Default operand size of segment
+ */
+unsigned char insn_get_seg_default_operand_bytes(struct pt_regs *regs)
+{
+ struct desc_struct *desc;
+ unsigned short seg;
+ int ret;
+
+ if (v8086_mode(regs))
+ return 2;
+
+ seg = (unsigned short)regs->cs;
+
+ ret = get_desc(seg, &desc);
+ if (ret)
+ return 0;
+
+ switch ((desc->l << 1) | desc->d) {
+ case 0: /* Legacy mode. 16-bit or 8-bit operands CS.L=0, CS.D=0 */
+ return 2;
+ case 1: /* Legacy mode. 32- or 8 bit operands CS.L=0, CS.D=1 */
+ /* fall through */
+ case 2: /* IA-32e 64-bit mode. 32- or 8-bit opnds. CS.L=1, CS.D=0 */
+ return 4;
+ case 3: /* Invalid setting. CS.L=1, CS.D=1 */
+ /* fall through */
+ default:
+ return 0;
+ }
+}
+
+/**
* insn_get_reg_offset_modrm_rm - Obtain register in r/m part of ModRM byte
* @insn: Instruction structure containing the ModRM byte
* @regs: Set of registers indicated by the ModRM byte
--
2.9.3
The segment descriptor contains information that is relevant to how linear
address need to be computed. It contains the default size of addresses as
well as the base address of the segment. Thus, given a segment selector,
we ought look at segment descriptor to correctly calculate the linear
address.
In protected mode, the segment selector might indicate a segment
descriptor from either the global descriptor table or a local descriptor
table. Both cases are considered in this function.
This function is the initial implementation for subsequent functions that
will obtain the aforementioned attributes of the segment descriptor.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Thomas Garnier <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/lib/insn-eval.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 61 insertions(+)
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 8d45df8..8608adf 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -5,9 +5,13 @@
*/
#include <linux/kernel.h>
#include <linux/string.h>
+#include <asm/desc_defs.h>
+#include <asm/desc.h>
#include <asm/inat.h>
#include <asm/insn.h>
#include <asm/insn-eval.h>
+#include <asm/ldt.h>
+#include <linux/mmu_context.h>
#include <asm/vm86.h>
enum reg_type {
@@ -294,6 +298,63 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
}
/**
+ * get_desc() - Obtain address of segment descriptor
+ * @seg: Segment selector
+ * @desc: Pointer to the selected segment descriptor
+ *
+ * Given a segment selector, obtain a memory pointer to the segment
+ * descriptor. Both global and local descriptor tables are supported.
+ * desc will contain the address of the descriptor.
+ *
+ * Return: 0 if success, -EINVAL if failure
+ */
+static int get_desc(unsigned short seg, struct desc_struct **desc)
+{
+ struct desc_ptr gdt_desc = {0, 0};
+ unsigned long desc_base;
+
+ if (!desc)
+ return -EINVAL;
+
+ desc_base = seg & ~(SEGMENT_RPL_MASK | SEGMENT_TI_MASK);
+
+#ifdef CONFIG_MODIFY_LDT_SYSCALL
+ if ((seg & SEGMENT_TI_MASK) == SEGMENT_LDT) {
+ seg >>= 3;
+
+ mutex_lock(¤t->active_mm->context.lock);
+ if (unlikely(!current->active_mm->context.ldt ||
+ seg >= current->active_mm->context.ldt->size)) {
+ *desc = NULL;
+ mutex_unlock(¤t->active_mm->context.lock);
+ return -EINVAL;
+ }
+
+ *desc = ¤t->active_mm->context.ldt->entries[seg];
+ mutex_unlock(¤t->active_mm->context.lock);
+ return 0;
+ }
+#endif
+ native_store_gdt(&gdt_desc);
+
+ /*
+ * Bits [15:3] of the segment selector contain the index. Such
+ * index needs to be multiplied by 8. However, as the index
+ * least significant bit is already in bit 3, we don't have
+ * to perform the multiplication.
+ */
+ desc_base = seg & ~(SEGMENT_RPL_MASK | SEGMENT_TI_MASK);
+
+ if (desc_base > gdt_desc.size) {
+ *desc = NULL;
+ return -EINVAL;
+ }
+
+ *desc = (struct desc_struct *)(gdt_desc.address + desc_base);
+ return 0;
+}
+
+/**
* insn_get_reg_offset_modrm_rm - Obtain register in r/m part of ModRM byte
* @insn: Instruction structure containing the ModRM byte
* @regs: Set of registers indicated by the ModRM byte
--
2.9.3
With segmentation, the base address of the segment descriptor is needed
to compute a linear address. The segment descriptor used in the address
computation depends on either any segment override prefixes in the in the
instruction or the default segment determined by the registers involved
in the address computation. Thus, both the instruction as well as the
register (specified as the offset from the base of pt_regs) are given as
inputs, along with a boolean variable to select between override and
default.
The segment selector is determined by get_seg_selector with the inputs
described above. Once the selector is known the base address is
determined. In protected mode, the selector is used to obtain the segment
descriptor and then its base address. If in 64-bit user mode, the segment =
base address is zero except when FS or GS are used. In virtual-8086 mode,
the base address is computed as the value of the segment selector shifted 4
positions to the left.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Thomas Garnier <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/include/asm/insn-eval.h | 2 ++
arch/x86/lib/insn-eval.c | 66 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 68 insertions(+)
diff --git a/arch/x86/include/asm/insn-eval.h b/arch/x86/include/asm/insn-eval.h
index 754211b..b201742 100644
--- a/arch/x86/include/asm/insn-eval.h
+++ b/arch/x86/include/asm/insn-eval.h
@@ -15,5 +15,7 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs);
int insn_get_reg_offset_modrm_rm(struct insn *insn, struct pt_regs *regs);
int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs);
int insn_get_reg_offset_sib_base(struct insn *insn, struct pt_regs *regs);
+unsigned long insn_get_seg_base(struct pt_regs *regs, struct insn *insn,
+ int regoff, bool use_default_seg);
#endif /* _ASM_X86_INSN_EVAL_H */
diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c
index 8608adf..383ca83 100644
--- a/arch/x86/lib/insn-eval.c
+++ b/arch/x86/lib/insn-eval.c
@@ -355,6 +355,72 @@ static int get_desc(unsigned short seg, struct desc_struct **desc)
}
/**
+ * insn_get_seg_base() - Obtain base address contained in descriptor
+ * @regs: Set of registers containing the segment selector
+ * @insn: Instruction structure with selector override prefixes
+ * @regoff: Operand offset, in pt_regs, of which the selector is needed
+ * @use_default_seg: Use the default segment instead of prefix overrides
+ *
+ * Obtain the base address of the segment descriptor as indicated by either
+ * any segment override prefixes contained in insn or the default segment
+ * applicable to the register indicated by regoff. regoff is specified as the
+ * offset in bytes from the base of pt_regs.
+ *
+ * Return: In protected mode, base address of the segment. It may be zero in
+ * certain cases for 64-bit builds and/or 64-bit applications. In virtual-8086
+ * mode, the segment selector shifed 4 positions to the right. -1L in case of
+ * error.
+ */
+unsigned long insn_get_seg_base(struct pt_regs *regs, struct insn *insn,
+ int regoff, bool use_default_seg)
+{
+ struct desc_struct *desc;
+ unsigned short seg;
+ enum segment seg_type;
+ int ret;
+
+ seg_type = resolve_seg_selector(insn, regoff, use_default_seg);
+
+ seg = get_segment_selector(regs, seg_type);
+ if (seg < 0)
+ return -1L;
+
+ if (v8086_mode(regs))
+ /*
+ * Base is simply the segment selector shifted 4
+ * positions to the right.
+ */
+ return (unsigned long)(seg << 4);
+
+#ifdef CONFIG_X86_64
+ if (user_64bit_mode(regs)) {
+ /*
+ * Only FS or GS will have a base address, the rest of
+ * the segments' bases are forced to 0.
+ */
+ unsigned long base;
+
+ if (seg_type == SEG_FS)
+ rdmsrl(MSR_FS_BASE, base);
+ else if (seg_type == SEG_GS)
+ /*
+ * swapgs was called at the kernel entry point. Thus,
+ * MSR_KERNEL_GS_BASE will have the user-space GS base.
+ */
+ rdmsrl(MSR_KERNEL_GS_BASE, base);
+ else
+ base = 0;
+ return base;
+ }
+#endif
+ ret = get_desc(seg, &desc);
+ if (ret)
+ return -1L;
+
+ return get_desc_base(desc);
+}
+
+/**
* insn_get_reg_offset_modrm_rm - Obtain register in r/m part of ModRM byte
* @insn: Instruction structure containing the ModRM byte
* @regs: Set of registers indicated by the ModRM byte
--
2.9.3
Even though memory addresses are unsigned. The operands used to compute the
effective address do have a sign. This is true for the r/m part of the
ModRM byte, the base and index parts of the SiB byte as well as the
displacement. Thus, signed variables shall be used when computing the
effective address from these operands. Once the signed effective address
has been computed, it is casted to an unsigned long to determine the
linear address.
Variables are renamed to better reflect the type of address being
computed.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Nathan Howard <[email protected]>
Cc: Adan Hawthorn <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/mm/mpx.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index 5126dfd..ff112e3 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -138,7 +138,8 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
*/
static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
{
- unsigned long addr, base, indx;
+ unsigned long linear_addr;
+ long eff_addr, base, indx;
int addr_offset, base_offset, indx_offset;
insn_byte_t sib;
@@ -150,7 +151,7 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
if (addr_offset < 0)
goto out_err;
- addr = regs_get_register(regs, addr_offset);
+ eff_addr = regs_get_register(regs, addr_offset);
} else {
if (insn->sib.nbytes) {
base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
@@ -163,16 +164,18 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
base = regs_get_register(regs, base_offset);
indx = regs_get_register(regs, indx_offset);
- addr = base + indx * (1 << X86_SIB_SCALE(sib));
+ eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
} else {
addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
if (addr_offset < 0)
goto out_err;
- addr = regs_get_register(regs, addr_offset);
+ eff_addr = regs_get_register(regs, addr_offset);
}
- addr += insn->displacement.value;
+ eff_addr += insn->displacement.value;
}
- return (void __user *)addr;
+ linear_addr = (unsigned long)eff_addr;
+
+ return (void __user *)linear_addr;
out_err:
return (void __user *)-1;
}
--
2.9.3
Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software
Developer's Manual volume 2A states that when memory addressing is used
(i.e., mod part of ModR/M is not 3), a SIB byte is used and the index of
the SIB byte points to the R/ESP (i.e., index = 4), the index should not be
used in the computation of the memory address.
In these cases the address is simply the value present in the register
pointed by the base part of the SIB byte plus the displacement byte.
An example of such instruction could be
insn -0x80(%rsp)
This is represented as:
[opcode] 4c 23 80
ModR/M=0x4c: mod: 0x1, reg: 0x1: r/m: 0x4(R/ESP)
SIB=0x23: sc: 0, index: 0x100(R/ESP), base: 0x11(R/EBX):
Displacement -0x80
The correct address is (base) + displacement; no index is used.
We can achieve the desired effect of not using the index by making
get_reg_offset return -EDOM in this particular case. This value indicates
callers that they should not use the index to calculate the address.
EINVAL continues to indicate that an error when decoding the SIB byte.
Care is taken to allow R12 to be used as index, which is a valid scenario.
Cc: Dave Hansen <[email protected]>
Cc: Adam Buchbinder <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Qiaowei Ren <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Nathan Howard <[email protected]>
Cc: Adan Hawthorn <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Ravi V. Shankar <[email protected]>
Cc: [email protected]
Signed-off-by: Ricardo Neri <[email protected]>
---
arch/x86/mm/mpx.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index ff112e3..d9e92d6 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -110,6 +110,13 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
regno = X86_SIB_INDEX(insn->sib.value);
if (X86_REX_X(insn->rex_prefix.value))
regno += 8;
+ /*
+ * If mod !=3, register R/ESP (regno=4) is not used as index in
+ * the address computation. Check is done after looking at REX.X
+ * This is because R12 (regno=12) can be used as an index.
+ */
+ if (regno == 4 && X86_MODRM_MOD(insn->modrm.value) != 3)
+ return -EDOM;
break;
case REG_TYPE_BASE:
@@ -159,11 +166,19 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
goto out_err;
indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
- if (indx_offset < 0)
+ /*
+ * A negative offset generally means a error, except
+ * -EDOM, which means that the contents of the register
+ * should not be used as index.
+ */
+ if (unlikely(indx_offset == -EDOM))
+ indx = 0;
+ else if (unlikely(indx_offset < 0))
goto out_err;
+ else
+ indx = regs_get_register(regs, indx_offset);
base = regs_get_register(regs, base_offset);
- indx = regs_get_register(regs, indx_offset);
eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
} else {
addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
--
2.9.3
On Fri, Mar 3, 2017 at 1:41 PM, Ricardo Neri
<[email protected]> wrote:
> fixup_umip_exception will be called from do_general_protection. If the
> former returns false, the latter will issue a SIGSEGV with SEND_SIG_PRIV.
> However, when emulation is successful but the emulated result cannot be
> copied to user space memory, it is more accurate to issue a SIGSEGV with
> SEGV_MAPERR with the offending address. A new function is inspired in
> force_sig_info_fault is introduced to model the page fault.
>
> Signed-off-by: Ricardo Neri <[email protected]>
> ---
> arch/x86/kernel/umip.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 43 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
> index e932f40..5b6a7cf 100644
> --- a/arch/x86/kernel/umip.c
> +++ b/arch/x86/kernel/umip.c
> @@ -170,6 +170,41 @@ static int __emulate_umip_insn(struct insn *insn, enum umip_insn umip_inst,
> }
>
> /**
> + * __force_sig_info_umip_fault - Force a SIGSEGV with SEGV_MAPERR
> + * @address: Address that caused the signal
> + * @regs: Register set containing the instruction pointer
> + *
> + * Force a SIGSEGV signal with SEGV_MAPERR as the error code. This function is
> + * intended to be used to provide a segmentation fault when the result of the
> + * UMIP emulation could not be copied to the user space memory.
> + *
> + * Return: none
> + */
> +static void __force_sig_info_umip_fault(void __user *address,
> + struct pt_regs *regs)
> +{
> + siginfo_t info;
> + struct task_struct *tsk = current;
> +
> + if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV)) {
> + printk_ratelimited("%s[%d] umip emulation segfault ip:%lx sp:%lx error:%lx in %lx\n",
> + tsk->comm, task_pid_nr(tsk), regs->ip,
> + regs->sp, UMIP_PF_USER | UMIP_PF_WRITE,
> + regs->ip);
> + }
> +
> + tsk->thread.cr2 = (unsigned long)address;
> + tsk->thread.error_code = UMIP_PF_USER | UMIP_PF_WRITE;
Please just move enum x86_pf_error_code into a header and rename the
fields X86_PF_USER, etc rather than duplicating it.
--Andy
On Sun, 2017-03-05 at 08:18 -0800, Andy Lutomirski wrote:
> > + */
> > +static void __force_sig_info_umip_fault(void __user *address,
> > + struct pt_regs *regs)
> > +{
> > + siginfo_t info;
> > + struct task_struct *tsk = current;
> > +
> > + if (show_unhandled_signals && unhandled_signal(tsk,
> SIGSEGV)) {
> > + printk_ratelimited("%s[%d] umip emulation segfault
> ip:%lx sp:%lx error:%lx in %lx\n",
> > + tsk->comm, task_pid_nr(tsk),
> regs->ip,
> > + regs->sp, UMIP_PF_USER |
> UMIP_PF_WRITE,
> > + regs->ip);
> > + }
> > +
> > + tsk->thread.cr2 = (unsigned long)address;
> > + tsk->thread.error_code = UMIP_PF_USER | UMIP_PF_WRITE;
>
> Please just move enum x86_pf_error_code into a header and rename the
> fields X86_PF_USER, etc rather than duplicating it.
Thanks again for your feedback! I will do this.