From: David Woodhouse <dwmw2@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Andi Kleen <ak@linux.intel.com>, Paul Turner <pjt@google.com>,
LKML <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linux-foundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
Dave Hansen <dave.hansen@intel.com>,
tglx@linutronix.de, Kees Cook <keescook@google.com>,
Rik van Riel <riel@redhat.com>,
Andy Lutomirski <luto@amacapital.net>,
Jiri Kosina <jikos@kernel.org>,
gnomes@lxorguk.ukuu.org.uk, x86@kernel.org, bp@alien8.de,
rga@amazon.de, thomas.lendacky@amd.com
Subject: Re: [PATCH v2.1] x86/retpoline: Fill return stack buffer on vmexit
Date: Thu, 11 Jan 2018 16:10:35 +0000 [thread overview]
Message-ID: <1515687035.22302.360.camel@infradead.org> (raw)
In-Reply-To: <20180111150419.2nsqst6qpifeq7k5@treble>
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On Thu, 2018-01-11 at 09:04 -0600, Josh Poimboeuf wrote:
>
> > How about this one then (with ANNOTATE_NOSPEC_ALTERNATIVE):
> >
> > - asm volatile (ALTERNATIVE("",
> > + asm volatile (ALTERNATIVE("jmp " alt_end_marker "f",
> > __stringify(__FILL_RETURN_BUFFER(%0, %1, _%=)),
> > X86_FEATURE_RETPOLINE)
> > : "=r" (dummy), ASM_CALL_CONSTRAINT : : "memory" );
>
> Looks good to me.
>
> Another IRC discussion was that Boris may eventually add a feature to
> the alternatives code to automatically insert such a jump if there are a
> lot of nops.
OK, v3 sent out with that. I've just manually put in a jump round it
(less hackishly than the alt_end_marker one) in the oldinstr for now.
This wants rolling into your objtool fixes:
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -119,7 +119,8 @@
*/
.macro FILL_RETURN_BUFFER reg:req nr:req ftr:req
#ifdef CONFIG_RETPOLINE
- ALTERNATIVE "jmp .Lskip_rsb_\@", \
+ ANNOTATE_NOSPEC_ALTERNATIVE
+ ALTERNATIVE "jmp .Lskip_rsb_\@", \
__stringify(__FILL_RETURN_BUFFER(\reg,\nr,%_ASM_SP,\@)) \
\ftr
.Lskip_rsb_\@:
@@ -149,6 +150,7 @@
# define THUNK_TARGET(addr) [thunk_target] "r" (addr)
#elif defined(CONFIG_X86_32) && defined(CONFIG_RETPOLINE)
+# define ANNOTATE_NOSPEC_ALTERNATIVE
/*
* For i386 we use the original ret-equivalent retpoline, because
* otherwise we'll run out of registers. We don't care about CET
@@ -201,7 +203,8 @@ static inline void vmexit_fill_RSB(void)
#ifdef CONFIG_RETPOLINE
unsigned long loops = RSB_CLEAR_LOOPS / 2;
- asm volatile (ALTERNATIVE("jmp .Lskip_rsb_%=",
+ asm volatile (ANNOTATE_NOSPEC_ALTERNATIVE
+ ALTERNATIVE("jmp .Lskip_rsb_%=",
__stringify(__FILL_RETURN_BUFFER(%0, RSB_CLEAR_LOOPS, %1, _%=)),
X86_FEATURE_RETPOLINE)
".Lskip_rsb_%=:"
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next prev parent reply other threads:[~2018-01-11 16:10 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-11 11:37 David Woodhouse
2018-01-11 12:26 ` Peter Zijlstra
2018-01-11 14:20 ` Josh Poimboeuf
2018-01-11 14:28 ` David Woodhouse
2018-01-11 14:32 ` Peter Zijlstra
2018-01-11 14:53 ` David Woodhouse
2018-01-11 15:04 ` Josh Poimboeuf
2018-01-11 16:10 ` David Woodhouse [this message]
2018-01-27 4:24 ` Konrad Rzeszutek Wilk
2018-01-11 15:22 ` Brian Gerst
2018-01-11 15:23 ` David Woodhouse
2018-01-11 15:28 ` Brian Gerst
2018-01-11 14:58 ` Josh Poimboeuf
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