x86-32: Use symbolic constants, safer CPUID when enabling EFER.NX
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>
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 050c278..7fd318b 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -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 @@
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