Add emulation of the sgdt, sidt, and smsw instructions for 64-bit
processes.
Wine users have encountered a number of 64-bit Windows games that use
these instructions (particularly sgdt), and were crashing when run on
UMIP-enabled systems.
Originally-by: Ricardo Neri <[email protected]>
Signed-off-by: Brendan Shanks <[email protected]>
---
arch/x86/kernel/umip.c | 55 +++++++++++++++++++++++++-----------------
1 file changed, 33 insertions(+), 22 deletions(-)
diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index 5b345add550f..1812e95d2f55 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -51,9 +51,7 @@
* The instruction smsw is emulated to return the value that the register CR0
* has at boot time as set in the head_32.
*
- * Also, emulation is provided only for 32-bit processes; 64-bit processes
- * that attempt to use the instructions that UMIP protects will receive the
- * SIGSEGV signal issued as a consequence of the general protection fault.
+ * Emulation is provided for both 32-bit and 64-bit processes.
*
* Care is taken to appropriately emulate the results when segmentation is
* used. That is, rather than relying on USER_DS and USER_CS, the function
@@ -63,17 +61,18 @@
* application uses a local descriptor table.
*/
-#define UMIP_DUMMY_GDT_BASE 0xfffe0000
-#define UMIP_DUMMY_IDT_BASE 0xffff0000
+#define UMIP_DUMMY_GDT_BASE 0xfffffffffffe0000ULL
+#define UMIP_DUMMY_IDT_BASE 0xffffffffffff0000ULL
/*
* The SGDT and SIDT instructions store the contents of the global descriptor
* table and interrupt table registers, respectively. The destination is a
* memory operand of X+2 bytes. X bytes are used to store the base address of
- * the table and 2 bytes are used to store the limit. In 32-bit processes, the
- * only processes for which emulation is provided, X has a value of 4.
+ * the table and 2 bytes are used to store the limit. In 32-bit processes X
+ * has a value of 4, in 64-bit processes X has a value of 8.
*/
-#define UMIP_GDT_IDT_BASE_SIZE 4
+#define UMIP_GDT_IDT_BASE_SIZE_64BIT 8
+#define UMIP_GDT_IDT_BASE_SIZE_32BIT 4
#define UMIP_GDT_IDT_LIMIT_SIZE 2
#define UMIP_INST_SGDT 0 /* 0F 01 /0 */
@@ -189,6 +188,7 @@ static int identify_insn(struct insn *insn)
* @umip_inst: A constant indicating the instruction to emulate
* @data: Buffer into which the dummy result is stored
* @data_size: Size of the emulated result
+ * @x86_64: true if process is 64-bit, false otherwise
*
* Emulate an instruction protected by UMIP and provide a dummy result. The
* result of the emulation is saved in @data. The size of the results depends
@@ -202,11 +202,8 @@ static int identify_insn(struct insn *insn)
* 0 on success, -EINVAL on error while emulating.
*/
static int emulate_umip_insn(struct insn *insn, int umip_inst,
- unsigned char *data, int *data_size)
+ unsigned char *data, int *data_size, bool x86_64)
{
- unsigned long dummy_base_addr, dummy_value;
- unsigned short dummy_limit = 0;
-
if (!data || !data_size || !insn)
return -EINVAL;
/*
@@ -219,6 +216,9 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
* is always returned irrespective of the operand size.
*/
if (umip_inst == UMIP_INST_SGDT || umip_inst == UMIP_INST_SIDT) {
+ u64 dummy_base_addr;
+ u16 dummy_limit = 0;
+
/* SGDT and SIDT do not use registers operands. */
if (X86_MODRM_MOD(insn->modrm.value) == 3)
return -EINVAL;
@@ -228,13 +228,24 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
else
dummy_base_addr = UMIP_DUMMY_IDT_BASE;
- *data_size = UMIP_GDT_IDT_LIMIT_SIZE + UMIP_GDT_IDT_BASE_SIZE;
+ /*
+ * 64-bit processes use the entire dummy base address.
+ * 32-bit processes use the lower 32 bits of the base address.
+ * dummy_base_addr is always 64 bits, but we memcpy the correct
+ * number of bytes from it to the destination.
+ */
+ if (x86_64)
+ *data_size = UMIP_GDT_IDT_BASE_SIZE_64BIT;
+ else
+ *data_size = UMIP_GDT_IDT_BASE_SIZE_32BIT;
+
+ memcpy(data + 2, &dummy_base_addr, *data_size);
- memcpy(data + 2, &dummy_base_addr, UMIP_GDT_IDT_BASE_SIZE);
+ *data_size += UMIP_GDT_IDT_LIMIT_SIZE;
memcpy(data, &dummy_limit, UMIP_GDT_IDT_LIMIT_SIZE);
} else if (umip_inst == UMIP_INST_SMSW) {
- dummy_value = CR0_STATE;
+ unsigned long dummy_value = CR0_STATE;
/*
* Even though the CR0 register has 4 bytes, the number
@@ -291,10 +302,9 @@ static void force_sig_info_umip_fault(void __user *addr, struct pt_regs *regs)
* @regs: Registers as saved when entering the #GP handler
*
* The instructions sgdt, sidt, str, smsw, sldt cause a general protection
- * fault if executed with CPL > 0 (i.e., from user space). If the offending
- * user-space process is not in long mode, this function fixes the exception
- * up and provides dummy results for sgdt, sidt and smsw; str and sldt are not
- * fixed up. Also long mode user-space processes are not fixed up.
+ * fault if executed with CPL > 0 (i.e., from user space). This function fixes
+ * the exception up and provides dummy results for sgdt, sidt and smsw; str
+ * and sldt are not fixed up.
*
* If operands are memory addresses, results are copied to user-space memory as
* indicated by the instruction pointed by eIP using the registers indicated in
@@ -373,13 +383,14 @@ bool fixup_umip_exception(struct pt_regs *regs)
umip_pr_warning(regs, "%s instruction cannot be used by applications.\n",
umip_insns[umip_inst]);
- /* Do not emulate SLDT, STR or user long mode processes. */
- if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT || user_64bit_mode(regs))
+ /* Do not emulate SLDT or STR. */
+ if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT)
return false;
umip_pr_warning(regs, "For now, expensive software emulation returns the result.\n");
- if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size))
+ if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size,
+ user_64bit_mode(regs)))
return false;
/*
--
2.17.1
On Thu, Sep 05, 2019 at 04:22:21PM -0700, Brendan Shanks wrote:
> Add emulation of the sgdt, sidt, and smsw instructions for 64-bit
> processes.
>
> Wine users have encountered a number of 64-bit Windows games that use
> these instructions (particularly sgdt), and were crashing when run on
> UMIP-enabled systems.
Emulation support for 64-bit processes was not initially included
because no use cases had been identified. Brendan has found one.
Here is the relevant e-mail thread: https://lkml.org/lkml/2017/1/26/12
FWIW,
Reviewed-by: Ricardo Neri <[email protected]>
Only one minor comment below...
>
> Originally-by: Ricardo Neri <[email protected]>
> Signed-off-by: Brendan Shanks <[email protected]>
> ---
> arch/x86/kernel/umip.c | 55 +++++++++++++++++++++++++-----------------
> 1 file changed, 33 insertions(+), 22 deletions(-)
>
> diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
> index 5b345add550f..1812e95d2f55 100644
> --- a/arch/x86/kernel/umip.c
> +++ b/arch/x86/kernel/umip.c
> @@ -51,9 +51,7 @@
> * The instruction smsw is emulated to return the value that the register CR0
> * has at boot time as set in the head_32.
> *
> - * Also, emulation is provided only for 32-bit processes; 64-bit processes
> - * that attempt to use the instructions that UMIP protects will receive the
> - * SIGSEGV signal issued as a consequence of the general protection fault.
> + * Emulation is provided for both 32-bit and 64-bit processes.
> *
> * Care is taken to appropriately emulate the results when segmentation is
> * used. That is, rather than relying on USER_DS and USER_CS, the function
> @@ -63,17 +61,18 @@
> * application uses a local descriptor table.
> */
>
> -#define UMIP_DUMMY_GDT_BASE 0xfffe0000
> -#define UMIP_DUMMY_IDT_BASE 0xffff0000
> +#define UMIP_DUMMY_GDT_BASE 0xfffffffffffe0000ULL
> +#define UMIP_DUMMY_IDT_BASE 0xffffffffffff0000ULL
>
> /*
> * The SGDT and SIDT instructions store the contents of the global descriptor
> * table and interrupt table registers, respectively. The destination is a
> * memory operand of X+2 bytes. X bytes are used to store the base address of
> - * the table and 2 bytes are used to store the limit. In 32-bit processes, the
> - * only processes for which emulation is provided, X has a value of 4.
> + * the table and 2 bytes are used to store the limit. In 32-bit processes X
> + * has a value of 4, in 64-bit processes X has a value of 8.
> */
> -#define UMIP_GDT_IDT_BASE_SIZE 4
> +#define UMIP_GDT_IDT_BASE_SIZE_64BIT 8
> +#define UMIP_GDT_IDT_BASE_SIZE_32BIT 4
> #define UMIP_GDT_IDT_LIMIT_SIZE 2
>
> #define UMIP_INST_SGDT 0 /* 0F 01 /0 */
> @@ -189,6 +188,7 @@ static int identify_insn(struct insn *insn)
> * @umip_inst: A constant indicating the instruction to emulate
> * @data: Buffer into which the dummy result is stored
> * @data_size: Size of the emulated result
> + * @x86_64: true if process is 64-bit, false otherwise
> *
> * Emulate an instruction protected by UMIP and provide a dummy result. The
> * result of the emulation is saved in @data. The size of the results depends
> @@ -202,11 +202,8 @@ static int identify_insn(struct insn *insn)
> * 0 on success, -EINVAL on error while emulating.
> */
> static int emulate_umip_insn(struct insn *insn, int umip_inst,
> - unsigned char *data, int *data_size)
> + unsigned char *data, int *data_size, bool x86_64)
> {
> - unsigned long dummy_base_addr, dummy_value;
> - unsigned short dummy_limit = 0;
> -
> if (!data || !data_size || !insn)
> return -EINVAL;
> /*
> @@ -219,6 +216,9 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
> * is always returned irrespective of the operand size.
> */
> if (umip_inst == UMIP_INST_SGDT || umip_inst == UMIP_INST_SIDT) {
> + u64 dummy_base_addr;
> + u16 dummy_limit = 0;
> +
> /* SGDT and SIDT do not use registers operands. */
> if (X86_MODRM_MOD(insn->modrm.value) == 3)
> return -EINVAL;
> @@ -228,13 +228,24 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
> else
> dummy_base_addr = UMIP_DUMMY_IDT_BASE;
>
> - *data_size = UMIP_GDT_IDT_LIMIT_SIZE + UMIP_GDT_IDT_BASE_SIZE;
Maybe a blank line here?
Thanks and BR,
Ricardo
On Sat, Sep 07, 2019 at 02:26:10PM -0700, Ricardo Neri wrote:
> > Wine users have encountered a number of 64-bit Windows games that use
> > these instructions (particularly sgdt), and were crashing when run on
> > UMIP-enabled systems.
>
> Emulation support for 64-bit processes was not initially included
> because no use cases had been identified.
AFAIR, we said at the time that 64-bit doesn't need it because this is
legacy software only and 64-bit will get fixed properly not to use those
insns. I can probably guess how that went ...
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
On September 6, 2019 12:22:21 AM GMT+01:00, Brendan Shanks <[email protected]> wrote:
>Add emulation of the sgdt, sidt, and smsw instructions for 64-bit
>processes.
>
>Wine users have encountered a number of 64-bit Windows games that use
>these instructions (particularly sgdt), and were crashing when run on
>UMIP-enabled systems.
>
>Originally-by: Ricardo Neri <[email protected]>
>Signed-off-by: Brendan Shanks <[email protected]>
>---
> arch/x86/kernel/umip.c | 55 +++++++++++++++++++++++++-----------------
> 1 file changed, 33 insertions(+), 22 deletions(-)
>
>diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
>index 5b345add550f..1812e95d2f55 100644
>--- a/arch/x86/kernel/umip.c
>+++ b/arch/x86/kernel/umip.c
>@@ -51,9 +51,7 @@
>* The instruction smsw is emulated to return the value that the
>register CR0
> * has at boot time as set in the head_32.
> *
>- * Also, emulation is provided only for 32-bit processes; 64-bit
>processes
>- * that attempt to use the instructions that UMIP protects will
>receive the
>- * SIGSEGV signal issued as a consequence of the general protection
>fault.
>+ * Emulation is provided for both 32-bit and 64-bit processes.
> *
>* Care is taken to appropriately emulate the results when segmentation
>is
>* used. That is, rather than relying on USER_DS and USER_CS, the
>function
>@@ -63,17 +61,18 @@
> * application uses a local descriptor table.
> */
>
>-#define UMIP_DUMMY_GDT_BASE 0xfffe0000
>-#define UMIP_DUMMY_IDT_BASE 0xffff0000
>+#define UMIP_DUMMY_GDT_BASE 0xfffffffffffe0000ULL
>+#define UMIP_DUMMY_IDT_BASE 0xffffffffffff0000ULL
>
> /*
>* The SGDT and SIDT instructions store the contents of the global
>descriptor
>* table and interrupt table registers, respectively. The destination is
>a
>* memory operand of X+2 bytes. X bytes are used to store the base
>address of
>- * the table and 2 bytes are used to store the limit. In 32-bit
>processes, the
>- * only processes for which emulation is provided, X has a value of 4.
>+ * the table and 2 bytes are used to store the limit. In 32-bit
>processes X
>+ * has a value of 4, in 64-bit processes X has a value of 8.
> */
>-#define UMIP_GDT_IDT_BASE_SIZE 4
>+#define UMIP_GDT_IDT_BASE_SIZE_64BIT 8
>+#define UMIP_GDT_IDT_BASE_SIZE_32BIT 4
> #define UMIP_GDT_IDT_LIMIT_SIZE 2
>
> #define UMIP_INST_SGDT 0 /* 0F 01 /0 */
>@@ -189,6 +188,7 @@ static int identify_insn(struct insn *insn)
> * @umip_inst: A constant indicating the instruction to emulate
> * @data: Buffer into which the dummy result is stored
> * @data_size: Size of the emulated result
>+ * @x86_64: true if process is 64-bit, false otherwise
> *
>* Emulate an instruction protected by UMIP and provide a dummy result.
>The
>* result of the emulation is saved in @data. The size of the results
>depends
>@@ -202,11 +202,8 @@ static int identify_insn(struct insn *insn)
> * 0 on success, -EINVAL on error while emulating.
> */
> static int emulate_umip_insn(struct insn *insn, int umip_inst,
>- unsigned char *data, int *data_size)
>+ unsigned char *data, int *data_size, bool x86_64)
> {
>- unsigned long dummy_base_addr, dummy_value;
>- unsigned short dummy_limit = 0;
>-
> if (!data || !data_size || !insn)
> return -EINVAL;
> /*
>@@ -219,6 +216,9 @@ static int emulate_umip_insn(struct insn *insn, int
>umip_inst,
> * is always returned irrespective of the operand size.
> */
> if (umip_inst == UMIP_INST_SGDT || umip_inst == UMIP_INST_SIDT) {
>+ u64 dummy_base_addr;
>+ u16 dummy_limit = 0;
>+
> /* SGDT and SIDT do not use registers operands. */
> if (X86_MODRM_MOD(insn->modrm.value) == 3)
> return -EINVAL;
>@@ -228,13 +228,24 @@ static int emulate_umip_insn(struct insn *insn,
>int umip_inst,
> else
> dummy_base_addr = UMIP_DUMMY_IDT_BASE;
>
>- *data_size = UMIP_GDT_IDT_LIMIT_SIZE + UMIP_GDT_IDT_BASE_SIZE;
>+ /*
>+ * 64-bit processes use the entire dummy base address.
>+ * 32-bit processes use the lower 32 bits of the base address.
>+ * dummy_base_addr is always 64 bits, but we memcpy the correct
>+ * number of bytes from it to the destination.
>+ */
>+ if (x86_64)
>+ *data_size = UMIP_GDT_IDT_BASE_SIZE_64BIT;
>+ else
>+ *data_size = UMIP_GDT_IDT_BASE_SIZE_32BIT;
>+
>+ memcpy(data + 2, &dummy_base_addr, *data_size);
>
>- memcpy(data + 2, &dummy_base_addr, UMIP_GDT_IDT_BASE_SIZE);
>+ *data_size += UMIP_GDT_IDT_LIMIT_SIZE;
> memcpy(data, &dummy_limit, UMIP_GDT_IDT_LIMIT_SIZE);
>
> } else if (umip_inst == UMIP_INST_SMSW) {
>- dummy_value = CR0_STATE;
>+ unsigned long dummy_value = CR0_STATE;
>
> /*
> * Even though the CR0 register has 4 bytes, the number
>@@ -291,10 +302,9 @@ static void force_sig_info_umip_fault(void __user
>*addr, struct pt_regs *regs)
> * @regs: Registers as saved when entering the #GP handler
> *
>* The instructions sgdt, sidt, str, smsw, sldt cause a general
>protection
>- * fault if executed with CPL > 0 (i.e., from user space). If the
>offending
>- * user-space process is not in long mode, this function fixes the
>exception
>- * up and provides dummy results for sgdt, sidt and smsw; str and sldt
>are not
>- * fixed up. Also long mode user-space processes are not fixed up.
>+ * fault if executed with CPL > 0 (i.e., from user space). This
>function fixes
>+ * the exception up and provides dummy results for sgdt, sidt and
>smsw; str
>+ * and sldt are not fixed up.
> *
>* If operands are memory addresses, results are copied to user-space
>memory as
>* indicated by the instruction pointed by eIP using the registers
>indicated in
>@@ -373,13 +383,14 @@ bool fixup_umip_exception(struct pt_regs *regs)
> umip_pr_warning(regs, "%s instruction cannot be used by
>applications.\n",
> umip_insns[umip_inst]);
>
>- /* Do not emulate SLDT, STR or user long mode processes. */
>- if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT ||
>user_64bit_mode(regs))
>+ /* Do not emulate SLDT or STR. */
>+ if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT)
> return false;
>
> umip_pr_warning(regs, "For now, expensive software emulation returns
>the result.\n");
>
>- if (emulate_umip_insn(&insn, umip_inst, dummy_data,
>&dummy_data_size))
>+ if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size,
>+ user_64bit_mode(regs)))
> return false;
>
> /*
I would strongly suggest that we change the term "emulation" to "spoofing" for these instructions. We need to explain that we do *not* execute these instructions the was the CPU would have, and unlike the native instructions do not leak kernel information.
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
> On Sep 7, 2019, at 2:26 PM, Ricardo Neri <[email protected]> wrote:
>
> On Thu, Sep 05, 2019 at 04:22:21PM -0700, Brendan Shanks wrote:
>>
>> if (umip_inst == UMIP_INST_SGDT || umip_inst == UMIP_INST_SIDT) {
>> + u64 dummy_base_addr;
>> + u16 dummy_limit = 0;
>> +
>> /* SGDT and SIDT do not use registers operands. */
>> if (X86_MODRM_MOD(insn->modrm.value) == 3)
>> return -EINVAL;
>> @@ -228,13 +228,24 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
>> else
>> dummy_base_addr = UMIP_DUMMY_IDT_BASE;
>>
>> - *data_size = UMIP_GDT_IDT_LIMIT_SIZE + UMIP_GDT_IDT_BASE_SIZE;
>
> Maybe a blank line here?
Adding a blank line in place of the removed line? I’m not sure I see the need for it, there’s already a blank line above, and it's followed by the block comment.
Brendan
* [email protected] <[email protected]> wrote:
> I would strongly suggest that we change the term "emulation" to
> "spoofing" for these instructions. We need to explain that we do *not*
> execute these instructions the was the CPU would have, and unlike the
> native instructions do not leak kernel information.
Ok, I've edited the patch to add the 'spoofing' wording where
appropriate, and I also made minor fixes such as consistently
capitalizing instruction names.
Can I also add your Reviewed-by tag?
So the patch should show up in tip:x86/asm today-ish, and barring any
complications is v5.4 material.
Thanks,
Ingo
On September 10, 2019 7:28:28 AM GMT+01:00, Ingo Molnar <[email protected]> wrote:
>
>* [email protected] <[email protected]> wrote:
>
>> I would strongly suggest that we change the term "emulation" to
>> "spoofing" for these instructions. We need to explain that we do
>*not*
>> execute these instructions the was the CPU would have, and unlike the
>
>> native instructions do not leak kernel information.
>
>Ok, I've edited the patch to add the 'spoofing' wording where
>appropriate, and I also made minor fixes such as consistently
>capitalizing instruction names.
>
>Can I also add your Reviewed-by tag?
>
>So the patch should show up in tip:x86/asm today-ish, and barring any
>complications is v5.4 material.
>
>Thanks,
>
> Ingo
Yes, please do.
Reviewed-by: H. Peter Anvin (Intel) <[email protected]>
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
The following commit has been merged into the x86/asm branch of tip:
Commit-ID: e86c2c8b9380440bbe761b8e2f63ab6b04a45ac2
Gitweb: https://git.kernel.org/tip/e86c2c8b9380440bbe761b8e2f63ab6b04a45ac2
Author: Brendan Shanks <[email protected]>
AuthorDate: Thu, 05 Sep 2019 16:22:21 -07:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Tue, 10 Sep 2019 08:36:16 +02:00
x86/umip: Add emulation (spoofing) for UMIP covered instructions in 64-bit processes as well
Add emulation (spoofing) of the SGDT, SIDT, and SMSW instructions for 64-bit
processes.
Wine users have encountered a number of 64-bit Windows games that use
these instructions (particularly SGDT), and were crashing when run on
UMIP-enabled systems.
Originally-by: Ricardo Neri <[email protected]>
Signed-off-by: Brendan Shanks <[email protected]>
Reviewed-by: Ricardo Neri <[email protected]>
Reviewed-by: H. Peter Anvin (Intel) <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: Eric W. Biederman <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
[ Minor edits: capitalization, added 'spoofing' wording. ]
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/x86/kernel/umip.c | 65 +++++++++++++++++++++++------------------
1 file changed, 38 insertions(+), 27 deletions(-)
diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index 5b345ad..548fefe 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -19,7 +19,7 @@
/** DOC: Emulation for User-Mode Instruction Prevention (UMIP)
*
* The feature User-Mode Instruction Prevention present in recent Intel
- * processor prevents a group of instructions (sgdt, sidt, sldt, smsw, and str)
+ * processor prevents a group of instructions (SGDT, SIDT, SLDT, SMSW and STR)
* from being executed with CPL > 0. Otherwise, a general protection fault is
* issued.
*
@@ -36,8 +36,8 @@
* DOSEMU2) rely on this subset of instructions to function.
*
* The instructions protected by UMIP can be split in two groups. Those which
- * return a kernel memory address (sgdt and sidt) and those which return a
- * value (sldt, str and smsw).
+ * return a kernel memory address (SGDT and SIDT) and those which 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,
@@ -45,15 +45,13 @@
* value that, lies close to the top of the kernel memory. The limit for the GDT
* and the IDT are set to zero.
*
- * Given that sldt and str are not commonly used in programs that run on WineHQ
+ * Given that SLDT and STR are not commonly used in programs that run on WineHQ
* or DOSEMU2, they are not emulated.
*
* The instruction smsw is emulated to return the value that the register CR0
* has at boot time as set in the head_32.
*
- * Also, emulation is provided only for 32-bit processes; 64-bit processes
- * that attempt to use the instructions that UMIP protects will receive the
- * SIGSEGV signal issued as a consequence of the general protection fault.
+ * Emulation is provided for both 32-bit and 64-bit processes.
*
* Care is taken to appropriately emulate the results when segmentation is
* used. That is, rather than relying on USER_DS and USER_CS, the function
@@ -63,17 +61,18 @@
* application uses a local descriptor table.
*/
-#define UMIP_DUMMY_GDT_BASE 0xfffe0000
-#define UMIP_DUMMY_IDT_BASE 0xffff0000
+#define UMIP_DUMMY_GDT_BASE 0xfffffffffffe0000ULL
+#define UMIP_DUMMY_IDT_BASE 0xffffffffffff0000ULL
/*
* The SGDT and SIDT instructions store the contents of the global descriptor
* table and interrupt table registers, respectively. The destination is a
* memory operand of X+2 bytes. X bytes are used to store the base address of
- * the table and 2 bytes are used to store the limit. In 32-bit processes, the
- * only processes for which emulation is provided, X has a value of 4.
+ * the table and 2 bytes are used to store the limit. In 32-bit processes X
+ * has a value of 4, in 64-bit processes X has a value of 8.
*/
-#define UMIP_GDT_IDT_BASE_SIZE 4
+#define UMIP_GDT_IDT_BASE_SIZE_64BIT 8
+#define UMIP_GDT_IDT_BASE_SIZE_32BIT 4
#define UMIP_GDT_IDT_LIMIT_SIZE 2
#define UMIP_INST_SGDT 0 /* 0F 01 /0 */
@@ -189,6 +188,7 @@ static int identify_insn(struct insn *insn)
* @umip_inst: A constant indicating the instruction to emulate
* @data: Buffer into which the dummy result is stored
* @data_size: Size of the emulated result
+ * @x86_64: true if process is 64-bit, false otherwise
*
* Emulate an instruction protected by UMIP and provide a dummy result. The
* result of the emulation is saved in @data. The size of the results depends
@@ -202,11 +202,8 @@ static int identify_insn(struct insn *insn)
* 0 on success, -EINVAL on error while emulating.
*/
static int emulate_umip_insn(struct insn *insn, int umip_inst,
- unsigned char *data, int *data_size)
+ unsigned char *data, int *data_size, bool x86_64)
{
- unsigned long dummy_base_addr, dummy_value;
- unsigned short dummy_limit = 0;
-
if (!data || !data_size || !insn)
return -EINVAL;
/*
@@ -219,6 +216,9 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
* is always returned irrespective of the operand size.
*/
if (umip_inst == UMIP_INST_SGDT || umip_inst == UMIP_INST_SIDT) {
+ u64 dummy_base_addr;
+ u16 dummy_limit = 0;
+
/* SGDT and SIDT do not use registers operands. */
if (X86_MODRM_MOD(insn->modrm.value) == 3)
return -EINVAL;
@@ -228,13 +228,24 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
else
dummy_base_addr = UMIP_DUMMY_IDT_BASE;
- *data_size = UMIP_GDT_IDT_LIMIT_SIZE + UMIP_GDT_IDT_BASE_SIZE;
+ /*
+ * 64-bit processes use the entire dummy base address.
+ * 32-bit processes use the lower 32 bits of the base address.
+ * dummy_base_addr is always 64 bits, but we memcpy the correct
+ * number of bytes from it to the destination.
+ */
+ if (x86_64)
+ *data_size = UMIP_GDT_IDT_BASE_SIZE_64BIT;
+ else
+ *data_size = UMIP_GDT_IDT_BASE_SIZE_32BIT;
+
+ memcpy(data + 2, &dummy_base_addr, *data_size);
- memcpy(data + 2, &dummy_base_addr, UMIP_GDT_IDT_BASE_SIZE);
+ *data_size += UMIP_GDT_IDT_LIMIT_SIZE;
memcpy(data, &dummy_limit, UMIP_GDT_IDT_LIMIT_SIZE);
} else if (umip_inst == UMIP_INST_SMSW) {
- dummy_value = CR0_STATE;
+ unsigned long dummy_value = CR0_STATE;
/*
* Even though the CR0 register has 4 bytes, the number
@@ -290,11 +301,10 @@ static void force_sig_info_umip_fault(void __user *addr, struct pt_regs *regs)
* fixup_umip_exception() - Fixup a general protection fault caused by UMIP
* @regs: Registers as saved when entering the #GP handler
*
- * The instructions sgdt, sidt, str, smsw, sldt cause a general protection
- * fault if executed with CPL > 0 (i.e., from user space). If the offending
- * user-space process is not in long mode, this function fixes the exception
- * up and provides dummy results for sgdt, sidt and smsw; str and sldt are not
- * fixed up. Also long mode user-space processes are not fixed up.
+ * The instructions SGDT, SIDT, STR, SMSW and SLDT cause a general protection
+ * fault if executed with CPL > 0 (i.e., from user space). This function fixes
+ * the exception up and provides dummy results for SGDT, SIDT and SMSW; STR
+ * and SLDT are not fixed up.
*
* If operands are memory addresses, results are copied to user-space memory as
* indicated by the instruction pointed by eIP using the registers indicated in
@@ -373,13 +383,14 @@ bool fixup_umip_exception(struct pt_regs *regs)
umip_pr_warning(regs, "%s instruction cannot be used by applications.\n",
umip_insns[umip_inst]);
- /* Do not emulate SLDT, STR or user long mode processes. */
- if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT || user_64bit_mode(regs))
+ /* Do not emulate (spoof) SLDT or STR. */
+ if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT)
return false;
umip_pr_warning(regs, "For now, expensive software emulation returns the result.\n");
- if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size))
+ if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size,
+ user_64bit_mode(regs)))
return false;
/*
On September 8, 2019 8:22:48 AM GMT+01:00, Borislav Petkov <[email protected]> wrote:
>On Sat, Sep 07, 2019 at 02:26:10PM -0700, Ricardo Neri wrote:
>> > Wine users have encountered a number of 64-bit Windows games that
>use
>> > these instructions (particularly sgdt), and were crashing when run
>on
>> > UMIP-enabled systems.
>>
>> Emulation support for 64-bit processes was not initially included
>> because no use cases had been identified.
>
>AFAIR, we said at the time that 64-bit doesn't need it because this is
>legacy software only and 64-bit will get fixed properly not to use
>those
>insns. I can probably guess how that went ...
I don't think Windows games was something we considered. However, needing to simulate these instructions is not a huge surprise. The important thing is that by simulating them, we can plug the leak of some very high value kernel information – mainly the GDT, IDT and TSS addresses.
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
* [email protected] <[email protected]> wrote:
> On September 10, 2019 7:28:28 AM GMT+01:00, Ingo Molnar <[email protected]> wrote:
> >
> >* [email protected] <[email protected]> wrote:
> >
> >> I would strongly suggest that we change the term "emulation" to
> >> "spoofing" for these instructions. We need to explain that we do
> >*not*
> >> execute these instructions the was the CPU would have, and unlike the
> >
> >> native instructions do not leak kernel information.
> >
> >Ok, I've edited the patch to add the 'spoofing' wording where
> >appropriate, and I also made minor fixes such as consistently
> >capitalizing instruction names.
> >
> >Can I also add your Reviewed-by tag?
> >
> >So the patch should show up in tip:x86/asm today-ish, and barring any
> >complications is v5.4 material.
> >
> >Thanks,
> >
> > Ingo
>
> Yes, please do.
>
> Reviewed-by: H. Peter Anvin (Intel) <[email protected]>
Thanks!
I've attached the updated version of the patch I'm testing.
Ingo
==================>
From e86c2c8b9380440bbe761b8e2f63ab6b04a45ac2 Mon Sep 17 00:00:00 2001
From: Brendan Shanks <[email protected]>
Date: Thu, 5 Sep 2019 16:22:21 -0700
Subject: [PATCH] x86/umip: Add emulation (spoofing) for UMIP covered instructions in 64-bit processes as well
Add emulation (spoofing) of the SGDT, SIDT, and SMSW instructions for 64-bit
processes.
Wine users have encountered a number of 64-bit Windows games that use
these instructions (particularly SGDT), and were crashing when run on
UMIP-enabled systems.
Originally-by: Ricardo Neri <[email protected]>
Signed-off-by: Brendan Shanks <[email protected]>
Reviewed-by: Ricardo Neri <[email protected]>
Reviewed-by: H. Peter Anvin (Intel) <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: Eric W. Biederman <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
[ Minor edits: capitalization, added 'spoofing' wording. ]
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/x86/kernel/umip.c | 65 +++++++++++++++++++++++++++++---------------------
1 file changed, 38 insertions(+), 27 deletions(-)
diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
index 5b345add550f..548fefed71ee 100644
--- a/arch/x86/kernel/umip.c
+++ b/arch/x86/kernel/umip.c
@@ -19,7 +19,7 @@
/** DOC: Emulation for User-Mode Instruction Prevention (UMIP)
*
* The feature User-Mode Instruction Prevention present in recent Intel
- * processor prevents a group of instructions (sgdt, sidt, sldt, smsw, and str)
+ * processor prevents a group of instructions (SGDT, SIDT, SLDT, SMSW and STR)
* from being executed with CPL > 0. Otherwise, a general protection fault is
* issued.
*
@@ -36,8 +36,8 @@
* DOSEMU2) rely on this subset of instructions to function.
*
* The instructions protected by UMIP can be split in two groups. Those which
- * return a kernel memory address (sgdt and sidt) and those which return a
- * value (sldt, str and smsw).
+ * return a kernel memory address (SGDT and SIDT) and those which 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,
@@ -45,15 +45,13 @@
* value that, lies close to the top of the kernel memory. The limit for the GDT
* and the IDT are set to zero.
*
- * Given that sldt and str are not commonly used in programs that run on WineHQ
+ * Given that SLDT and STR are not commonly used in programs that run on WineHQ
* or DOSEMU2, they are not emulated.
*
* The instruction smsw is emulated to return the value that the register CR0
* has at boot time as set in the head_32.
*
- * Also, emulation is provided only for 32-bit processes; 64-bit processes
- * that attempt to use the instructions that UMIP protects will receive the
- * SIGSEGV signal issued as a consequence of the general protection fault.
+ * Emulation is provided for both 32-bit and 64-bit processes.
*
* Care is taken to appropriately emulate the results when segmentation is
* used. That is, rather than relying on USER_DS and USER_CS, the function
@@ -63,17 +61,18 @@
* application uses a local descriptor table.
*/
-#define UMIP_DUMMY_GDT_BASE 0xfffe0000
-#define UMIP_DUMMY_IDT_BASE 0xffff0000
+#define UMIP_DUMMY_GDT_BASE 0xfffffffffffe0000ULL
+#define UMIP_DUMMY_IDT_BASE 0xffffffffffff0000ULL
/*
* The SGDT and SIDT instructions store the contents of the global descriptor
* table and interrupt table registers, respectively. The destination is a
* memory operand of X+2 bytes. X bytes are used to store the base address of
- * the table and 2 bytes are used to store the limit. In 32-bit processes, the
- * only processes for which emulation is provided, X has a value of 4.
+ * the table and 2 bytes are used to store the limit. In 32-bit processes X
+ * has a value of 4, in 64-bit processes X has a value of 8.
*/
-#define UMIP_GDT_IDT_BASE_SIZE 4
+#define UMIP_GDT_IDT_BASE_SIZE_64BIT 8
+#define UMIP_GDT_IDT_BASE_SIZE_32BIT 4
#define UMIP_GDT_IDT_LIMIT_SIZE 2
#define UMIP_INST_SGDT 0 /* 0F 01 /0 */
@@ -189,6 +188,7 @@ static int identify_insn(struct insn *insn)
* @umip_inst: A constant indicating the instruction to emulate
* @data: Buffer into which the dummy result is stored
* @data_size: Size of the emulated result
+ * @x86_64: true if process is 64-bit, false otherwise
*
* Emulate an instruction protected by UMIP and provide a dummy result. The
* result of the emulation is saved in @data. The size of the results depends
@@ -202,11 +202,8 @@ static int identify_insn(struct insn *insn)
* 0 on success, -EINVAL on error while emulating.
*/
static int emulate_umip_insn(struct insn *insn, int umip_inst,
- unsigned char *data, int *data_size)
+ unsigned char *data, int *data_size, bool x86_64)
{
- unsigned long dummy_base_addr, dummy_value;
- unsigned short dummy_limit = 0;
-
if (!data || !data_size || !insn)
return -EINVAL;
/*
@@ -219,6 +216,9 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
* is always returned irrespective of the operand size.
*/
if (umip_inst == UMIP_INST_SGDT || umip_inst == UMIP_INST_SIDT) {
+ u64 dummy_base_addr;
+ u16 dummy_limit = 0;
+
/* SGDT and SIDT do not use registers operands. */
if (X86_MODRM_MOD(insn->modrm.value) == 3)
return -EINVAL;
@@ -228,13 +228,24 @@ static int emulate_umip_insn(struct insn *insn, int umip_inst,
else
dummy_base_addr = UMIP_DUMMY_IDT_BASE;
- *data_size = UMIP_GDT_IDT_LIMIT_SIZE + UMIP_GDT_IDT_BASE_SIZE;
+ /*
+ * 64-bit processes use the entire dummy base address.
+ * 32-bit processes use the lower 32 bits of the base address.
+ * dummy_base_addr is always 64 bits, but we memcpy the correct
+ * number of bytes from it to the destination.
+ */
+ if (x86_64)
+ *data_size = UMIP_GDT_IDT_BASE_SIZE_64BIT;
+ else
+ *data_size = UMIP_GDT_IDT_BASE_SIZE_32BIT;
+
+ memcpy(data + 2, &dummy_base_addr, *data_size);
- memcpy(data + 2, &dummy_base_addr, UMIP_GDT_IDT_BASE_SIZE);
+ *data_size += UMIP_GDT_IDT_LIMIT_SIZE;
memcpy(data, &dummy_limit, UMIP_GDT_IDT_LIMIT_SIZE);
} else if (umip_inst == UMIP_INST_SMSW) {
- dummy_value = CR0_STATE;
+ unsigned long dummy_value = CR0_STATE;
/*
* Even though the CR0 register has 4 bytes, the number
@@ -290,11 +301,10 @@ static void force_sig_info_umip_fault(void __user *addr, struct pt_regs *regs)
* fixup_umip_exception() - Fixup a general protection fault caused by UMIP
* @regs: Registers as saved when entering the #GP handler
*
- * The instructions sgdt, sidt, str, smsw, sldt cause a general protection
- * fault if executed with CPL > 0 (i.e., from user space). If the offending
- * user-space process is not in long mode, this function fixes the exception
- * up and provides dummy results for sgdt, sidt and smsw; str and sldt are not
- * fixed up. Also long mode user-space processes are not fixed up.
+ * The instructions SGDT, SIDT, STR, SMSW and SLDT cause a general protection
+ * fault if executed with CPL > 0 (i.e., from user space). This function fixes
+ * the exception up and provides dummy results for SGDT, SIDT and SMSW; STR
+ * and SLDT are not fixed up.
*
* If operands are memory addresses, results are copied to user-space memory as
* indicated by the instruction pointed by eIP using the registers indicated in
@@ -373,13 +383,14 @@ bool fixup_umip_exception(struct pt_regs *regs)
umip_pr_warning(regs, "%s instruction cannot be used by applications.\n",
umip_insns[umip_inst]);
- /* Do not emulate SLDT, STR or user long mode processes. */
- if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT || user_64bit_mode(regs))
+ /* Do not emulate (spoof) SLDT or STR. */
+ if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT)
return false;
umip_pr_warning(regs, "For now, expensive software emulation returns the result.\n");
- if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size))
+ if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size,
+ user_64bit_mode(regs)))
return false;
/*