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Commit 96e5d28a authored by Borislav Petkov's avatar Borislav Petkov Committed by Ingo Molnar
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x86/cpu: Add Erratum 88 detection on AMD 



Erratum 88 affects old AMD K8s, where a SWAPGS fails to cause an input
dependency on GS. Therefore, we need to MFENCE before it.

But that MFENCE is expensive and unnecessary on the remaining x86 CPUs
out there so patch it out on the CPUs which don't require it.

Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rudolf Marek <r.marek@assembler.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/aec6b2df1bfc56101d4e9e2e5d5d570bf41663c6.1460075211.git.luto@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 0230bb03

arch/x86/entry/entry_64.S

+1 −1
Original line number Diff line number Diff line
@@ -783,7 +783,7 @@ ENTRY(native_load_gs_index) 
	SWAPGS

gs_change:

	movl	%edi, %gs

2:	mfence					/* workaround */

2:	ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE

	SWAPGS

	popfq

	ret

arch/x86/include/asm/cpufeatures.h

+2 −0
Original line number Diff line number Diff line
@@ -295,6 +295,8 @@ 
#define X86_BUG_CLFLUSH_MONITOR	X86_BUG(7) /* AAI65, CLFLUSH required before MONITOR */

#define X86_BUG_SYSRET_SS_ATTRS	X86_BUG(8) /* SYSRET doesn't fix up SS attrs */

#define X86_BUG_NULL_SEG	X86_BUG(9) /* Nulling a selector preserves the base */

#define X86_BUG_SWAPGS_FENCE	X86_BUG(10) /* SWAPGS without input dep on GS */





#ifdef CONFIG_X86_32

/*

arch/x86/kernel/cpu/amd.c

+1 −0
Original line number Diff line number Diff line
@@ -632,6 +632,7 @@ static void init_amd_k8(struct cpuinfo_x86 *c) 
	 */

	msr_set_bit(MSR_K7_HWCR, 6);

#endif

	set_cpu_bug(c, X86_BUG_SWAPGS_FENCE);

}



static void init_amd_gh(struct cpuinfo_x86 *c)