Resending with updates to commit messages and Pekka Enberg's Acks.
Intel CPUs have an additional MSR bit to indicate if the BIOS was
configured to disable NX. This bit was traditionally used for operating
systems that did not understand how to handle the NX bit. Since Linux
understands this, this BIOS flag should be ignored by default.
In a review[1] of reported hardware being used by Ubuntu bug reporters,
almost 10% of systems had an incorrectly configured BIOS, leaving their
systems unable to use the NX features of their CPU.
This change will clear the MSR_IA32_MISC_ENABLE_XD_DISABLE bit so that NX
cannot be inappropriately controlled by the BIOS on Intel CPUs. If, under
very strange hardware configurations, NX actually needs to be disabled,
"noexec=off" can be used to restore the prior behavior.
-Kees
[1] http://www.outflux.net/blog/archives/2010/02/18/data-mining-for-nx-bit/
---
Changelog:
v2 - rearranged use of verify_cpu()
v3 - resent, show stats on systems that need it
v4 - expanded commit messages, added acks
--
Kees Cook
Ubuntu Security Team
The code is 32bit already, and can be used in 32bit routines.
Signed-off-by: Kees Cook <[email protected]>
Acked-by: Pekka Enberg <[email protected]>
---
arch/x86/boot/compressed/head_64.S | 2 +-
arch/x86/kernel/trampoline_64.S | 2 +-
arch/x86/kernel/{verify_cpu_64.S => verify_cpu.S} | 0
3 files changed, 2 insertions(+), 2 deletions(-)
rename arch/x86/kernel/{verify_cpu_64.S => verify_cpu.S} (100%)
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 52f85a1..35af09d 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -182,7 +182,7 @@ no_longmode:
hlt
jmp 1b
-#include "../../kernel/verify_cpu_64.S"
+#include "../../kernel/verify_cpu.S"
/*
* Be careful here startup_64 needs to be at a predictable
diff --git a/arch/x86/kernel/trampoline_64.S b/arch/x86/kernel/trampoline_64.S
index 3af2dff..075d130 100644
--- a/arch/x86/kernel/trampoline_64.S
+++ b/arch/x86/kernel/trampoline_64.S
@@ -127,7 +127,7 @@ startup_64:
no_longmode:
hlt
jmp no_longmode
-#include "verify_cpu_64.S"
+#include "verify_cpu.S"
# Careful these need to be in the same 64K segment as the above;
tidt:
diff --git a/arch/x86/kernel/verify_cpu_64.S b/arch/x86/kernel/verify_cpu.S
similarity index 100%
rename from arch/x86/kernel/verify_cpu_64.S
rename to arch/x86/kernel/verify_cpu.S
--
1.7.2.3
--
Kees Cook
Ubuntu Security Team
Intel CPUs have an additional MSR bit to indicate if the BIOS was
configured to disable the NX cpu feature. This bit was traditionally
used for operating systems that did not understand how to handle the
NX bit. Since Linux understands this, this BIOS flag should be ignored
by default.
In a review[1] of reported hardware being used by Ubuntu bug reporters,
almost 10% of systems had an incorrectly configured BIOS, leaving their
systems unable to use the NX features of their CPU.
This change will clear the MSR_IA32_MISC_ENABLE_XD_DISABLE bit so that NX
cannot be inappropriately controlled by the BIOS on Intel CPUs. If, under
very strange hardware configurations, NX actually needs to be disabled,
"noexec=off" can be used to restore the prior behavior.
[1] http://www.outflux.net/blog/archives/2010/02/18/data-mining-for-nx-bit/
Signed-off-by: Kees Cook <[email protected]>
Acked-by: Pekka Enberg <[email protected]>
---
arch/x86/kernel/verify_cpu.S | 48 +++++++++++++++++++++++++++++++++++-------
1 files changed, 40 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kernel/verify_cpu.S b/arch/x86/kernel/verify_cpu.S
index 56a8c2a..ccb4136 100644
--- a/arch/x86/kernel/verify_cpu.S
+++ b/arch/x86/kernel/verify_cpu.S
@@ -7,6 +7,7 @@
* Copyright (c) 2007 Andi Kleen ([email protected])
* Copyright (c) 2007 Eric Biederman ([email protected])
* Copyright (c) 2007 Vivek Goyal ([email protected])
+ * Copyright (c) 2010 Kees Cook ([email protected])
*
* This source code is licensed under the GNU General Public License,
* Version 2. See the file COPYING for more details.
@@ -14,18 +15,16 @@
* This is a common code for verification whether CPU supports
* long mode and SSE or not. It is not called directly instead this
* file is included at various places and compiled in that context.
- * Following are the current usage.
+ * This file is expected to run in 32bit code. Currently:
*
- * This file is included by both 16bit and 32bit code.
+ * arch/x86_64/boot/compressed/head_64.S: Boot cpu verification
+ * arch/x86_64/kernel/trampoline_64.S: secondary processor verfication
*
- * arch/x86_64/boot/setup.S : Boot cpu verification (16bit)
- * arch/x86_64/boot/compressed/head.S: Boot cpu verification (32bit)
- * arch/x86_64/kernel/trampoline.S: secondary processor verfication (16bit)
- * arch/x86_64/kernel/acpi/wakeup.S:Verfication at resume (16bit)
- *
- * verify_cpu, returns the status of cpu check in register %eax.
+ * verify_cpu, returns the status of longmode and SSE in register %eax.
* 0: Success 1: Failure
*
+ * On Intel, the XD_DISABLE flag will be cleared as a side-effect.
+ *
* The caller needs to check for the error code and take the action
* appropriately. Either display a message or halt.
*/
@@ -62,8 +61,41 @@ verify_cpu:
cmpl $0x444d4163,%ecx
jnz verify_cpu_noamd
mov $1,%di # cpu is from AMD
+ jmp verify_cpu_check
verify_cpu_noamd:
+ cmpl $0x756e6547,%ebx # GenuineIntel?
+ jnz verify_cpu_check
+ cmpl $0x49656e69,%edx
+ jnz verify_cpu_check
+ cmpl $0x6c65746e,%ecx
+ jnz verify_cpu_check
+
+ # only call IA32_MISC_ENABLE when:
+ # family > 6 || (family == 6 && model >= 0xd)
+ movl $0x1, %eax # check CPU family and model
+ cpuid
+ movl %eax, %ecx
+
+ andl $0x0ff00f00, %eax # mask family and extended family
+ shrl $8, %eax
+ cmpl $6, %eax
+ ja verify_cpu_clear_xd # family > 6, ok
+ jb verify_cpu_check # family < 6, skip
+
+ andl $0x000f00f0, %ecx # mask model and extended model
+ shrl $4, %ecx
+ cmpl $0xd, %ecx
+ jb verify_cpu_check # family == 6, model < 0xd, skip
+
+verify_cpu_clear_xd:
+ movl $MSR_IA32_MISC_ENABLE, %ecx
+ rdmsr
+ btrl $2, %edx # clear MSR_IA32_MISC_ENABLE_XD_DISABLE
+ jnc verify_cpu_check # only write MSR if bit was changed
+ wrmsr
+
+verify_cpu_check:
movl $0x1,%eax # Does the cpu have what it takes
cpuid
andl $REQUIRED_MASK0,%edx
--
1.7.2.3
--
Kees Cook
Ubuntu Security Team
The XD_DISABLE-clearing side-effect needs to happen for both 32bit
and 64bit, but the 32bit init routines were not calling verify_cpu()
yet. This adds that call to gain the side-effect.
The longmode/SSE tests being performed in verify_cpu() need to happen very
early for 64bit but not for 32bit. Instead of including it in two places
for 32bit, we can just include it once in arch/x86/kernel/head_32.S.
Signed-off-by: Kees Cook <[email protected]>
Acked-by: Pekka Enberg <[email protected]>
---
arch/x86/kernel/head_32.S | 6 ++++++
arch/x86/kernel/verify_cpu.S | 1 +
2 files changed, 7 insertions(+), 0 deletions(-)
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index bcece91..fdaea52 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -314,6 +314,10 @@ ENTRY(startup_32_smp)
subl $0x80000001, %eax
cmpl $(0x8000ffff-0x80000001), %eax
ja 6f
+
+ /* Clear bogus XD_DISABLE bits */
+ call verify_cpu
+
mov $0x80000001, %eax
cpuid
/* Execute Disable bit supported? */
@@ -609,6 +613,8 @@ ignore_int:
#endif
iret
+#include "verify_cpu.S"
+
__REFDATA
.align 4
ENTRY(initial_code)
diff --git a/arch/x86/kernel/verify_cpu.S b/arch/x86/kernel/verify_cpu.S
index ccb4136..5644b4b 100644
--- a/arch/x86/kernel/verify_cpu.S
+++ b/arch/x86/kernel/verify_cpu.S
@@ -19,6 +19,7 @@
*
* arch/x86_64/boot/compressed/head_64.S: Boot cpu verification
* arch/x86_64/kernel/trampoline_64.S: secondary processor verfication
+ * arch/x86_64/kernel/head_32.S: processor startup
*
* verify_cpu, returns the status of longmode and SSE in register %eax.
* 0: Success 1: Failure
--
1.7.2.3
--
Kees Cook
Ubuntu Security Team
Fix the NX feature boot warning when NX is missing to correctly
reflect that BIOSes cannot disable NX now.
Signed-off-by: Kees Cook <[email protected]>
Acked-by: Pekka Enberg <[email protected]>
---
arch/x86/mm/setup_nx.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/arch/x86/mm/setup_nx.c b/arch/x86/mm/setup_nx.c
index a3250aa..410531d 100644
--- a/arch/x86/mm/setup_nx.c
+++ b/arch/x86/mm/setup_nx.c
@@ -41,7 +41,7 @@ void __init x86_report_nx(void)
{
if (!cpu_has_nx) {
printk(KERN_NOTICE "Notice: NX (Execute Disable) protection "
- "missing in CPU or disabled in BIOS!\n");
+ "missing in CPU!\n");
} else {
#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
if (disable_nx) {
--
1.7.2.3
--
Kees Cook
Ubuntu Security Team