Commit 8a50e513 authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

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: default avatarH. Peter Anvin <hpa@zytor.com>
LKML-Reference: <1258154897-6770-2-git-send-email-hpa@zytor.com>
Acked-by: default avatarKees Cook <kees.cook@canonical.com>
parent 196cf0d6

arch/x86/kernel/head_32.S

+11 −7
Original line number Diff line number Diff line
@@ -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

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