Re: [PATCH] x86_64, asm: Work around AMD SYSRET SS descriptor attribute issue

[Borislav Petkov]

On Mon, Apr 27, 2015 at 12:07:14PM +0200, Denys Vlasenko wrote:
> 	/* Only three 0x66 prefixes for NOP for fast decode on all CPUs */
> 	ALTERNATIVE	".byte 0x66,0x66,0x66,0x90 \
> 			.byte 0x66,0x66,0x66,0x90 \
> 			.byte 0x66,0x66,0x66,0x90",
> 			"shl	$(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx \
> 			sar	$(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx \
> 			cmpq	%rcx, %r11 \
> 			jne	opportunistic_sysret_failed"
> 			X86_BUG_SYSRET_CANONICAL_RCX
> 
> would be better than letting ALTERNATIVE to generate 13 one-byte NOPs.

We already do everything automagically, see:
arch/x86/kernel/alternative.c: optimize_nops()

:-)

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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