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x86-32: Use symbolic constants, safer CPUID when enabling EFER.NX

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Use symbolic constants rather than hard-coded values when setting
EFER.NX in head_32.S, and do a more rigorous test for the validity of
the response when probing for the extended CPUID range.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <1258154897-6770-2-git-send-email-hpa@zytor.com>
Acked-by: Kees Cook <kees.cook@canonical.com>
This commit is contained in:
H. Peter Anvin 2009-11-13 15:28:13 -08:00
parent 196cf0d67a
commit 8a50e5135a
1 changed files with 11 additions and 7 deletions
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18
arch/x86/kernel/head_32.S
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@ -18,6 +18,8 @@
#include <asm/asm-offsets.h>
#include <asm/setup.h>
#include <asm/processor-flags.h>
#include <asm/msr-index.h>
#include <asm/cpufeature.h>
#include <asm/percpu.h>
/* Physical address */
@ -297,25 +299,27 @@ ENTRY(startup_32_smp)
orl %edx,%eax
movl %eax,%cr4
btl $5, %eax # check if PAE is enabled
jnc 6f
testb $X86_CR4_PAE, %al # check if PAE is enabled
jz 6f
/* Check if extended functions are implemented */
movl $0x80000000, %eax
cpuid
cmpl $0x80000000, %eax
jbe 6f
/* Value must be in the range 0x80000001 to 0x8000ffff */
subl $0x80000001, %eax
cmpl $(0x8000ffff-0x80000001), %eax
ja 6f
mov $0x80000001, %eax
cpuid
/* Execute Disable bit supported? */
btl $20, %edx
btl $(X86_FEATURE_NX & 31), %edx
jnc 6f
/* Setup EFER (Extended Feature Enable Register) */
movl $0xc0000080, %ecx
movl $MSR_EFER, %ecx
rdmsr
btsl $11, %eax
btsl $_EFER_NX, %eax
/* Make changes effective */
wrmsr