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From: "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, keescook@chromium.org,
	hjl.tools@gmail.com, andrew.cooper3@citrix.com,
	mark.rutland@arm.com, will@kernel.org, ndesaulniers@google.com,
	x86@kernel.org, Ankur Arora <ankur.a.arora@oracle.com>
Subject: Missing SLS int3 in JMP_NOSPEC? (Was: [PATCH v2 6/6] x86: Add straight-line-speculation mitigation)
Date: Tue, 19 Jul 2022 15:19:26 +0200	[thread overview]
Message-ID: <9011132e-d78b-8bec-10cb-2b3d77a4e1fc@maciej.szmigiero.name> (raw)
In-Reply-To: <20211204134908.140103474@infradead.org>

On 4.12.2021 14:43, Peter Zijlstra wrote:
> Make use of an upcomming GCC feature to mitigate
> straight-line-speculation for x86:
> 
>    https://gcc.gnu.org/g:53a643f8568067d7700a9f2facc8ba39974973d3
>    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102952
>    https://bugs.llvm.org/show_bug.cgi?id=52323
> 
> It's built tested on x86_64-allyesconfig using GCC-12 and GCC-11.
> 
> Maintenace overhead of this should be fairly low due to objtool
> validation.
> 
> Size overhead of all these additional int3 instructions comes to:
> 
>     text	   data	    bss	    dec	    hex	filename
> 22267751	6933356	2011368	31212475	1dc43bb	defconfig-build/vmlinux
> 22804126	6933356	1470696	31208178	1dc32f2	defconfig-build/vmlinux.sls
> 
> Or roughly 2.4% additional text.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
(..)
> --- a/arch/x86/lib/retpoline.S
> +++ b/arch/x86/lib/retpoline.S
> @@ -34,7 +34,7 @@ SYM_INNER_LABEL(__x86_indirect_thunk_\re
>   
>   	ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
>   		      __stringify(RETPOLINE \reg), X86_FEATURE_RETPOLINE, \
> -		      __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_AMD
> +		      __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg; int3), X86_FEATURE_RETPOLINE_AMD
>   
>   .endm
>   

Looking at this __x86_indirect_thunk_* change makes me wonder why there is
no similar int3 SLS protection in the X86_FEATURE_RETPOLINE_LFENCE case of
JMP_NOSPEC in arch/x86/include/asm/nospec-branch.h:
> .macro JMP_NOSPEC reg:req
> #ifdef CONFIG_RETPOLINE
> 	ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
> 		      __stringify(jmp __x86_indirect_thunk_\reg), X86_FEATURE_RETPOLINE, \
> 		      __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_LFENCE
> #else

JMP_NOSPEC users seem to have no explicit trailing int3 instructions
either.

Or am I missing something here?

Thanks,
Maciej

  parent reply	other threads:[~2022-07-19 14:06 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-04 13:43 [PATCH v2 0/6] x86: Add stright-line-speculation mitigations Peter Zijlstra
2021-12-04 13:43 ` [PATCH v2 1/6] x86/atomic64_386_32: Rename things Peter Zijlstra
2021-12-10 11:05   ` [tip: x86/core] x86/lib/atomic64_386_32: " tip-bot2 for Peter Zijlstra
2021-12-04 13:43 ` [PATCH v2 2/6] x86: Prepare asm files for straight-line-speculation Peter Zijlstra
2021-12-10 11:05   ` [tip: x86/core] " tip-bot2 for Peter Zijlstra
2021-12-04 13:43 ` [PATCH v2 3/6] x86: Prepare inline-asm " Peter Zijlstra
2021-12-10 11:05   ` [tip: x86/core] " tip-bot2 for Peter Zijlstra
2021-12-04 13:43 ` [PATCH v2 4/6] objtool: Add straight-line-speculation validation Peter Zijlstra
2021-12-10 11:05   ` [tip: x86/core] " tip-bot2 for Peter Zijlstra
2021-12-04 13:43 ` [PATCH v2 5/6] x86/alternative: Relax text_poke_bp() constraint Peter Zijlstra
2021-12-10 11:05   ` [tip: x86/core] " tip-bot2 for Peter Zijlstra
2021-12-04 13:43 ` [PATCH v2 6/6] x86: Add straight-line-speculation mitigation Peter Zijlstra
2021-12-10 11:05   ` [tip: x86/core] " tip-bot2 for Peter Zijlstra
2022-07-19 13:19   ` Maciej S. Szmigiero [this message]
2022-07-19 21:23     ` [RFC][PATCH] x86,nospec: Simplify {JMP,CALL}_NOSPEC Peter Zijlstra
2022-07-19 21:33       ` Peter Zijlstra
2022-07-20  0:01         ` Maciej S. Szmigiero
2022-07-20  9:12           ` Peter Zijlstra

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