lkml.org 
[lkml]   [2018]   [Feb]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH 2/2] x86/retpoline: Fix return buffer filling
On Mon, Feb 12, 2018 at 04:04:22PM -0800, Andi Kleen wrote:
> From: Andi Kleen <ak@linux.intel.com>
>
> An earlier patch moved the RSB filling out of line, ending
> it with a return. This results in the return buffer filling
> only giving 15 instead of 16 usable returns because
> the return from fill_rsb already uses one up.
>
> Since the kernel call chains can be quite deep that's
> somewhat dangerous and better avoided.
>
> Always do one extra return buffer fill in the caller.
> I added a STUFF_ONE_RSB macro for this, and fixed
> up all the caller
>
> An alternative would be to revert 1dde7415e999
> and just go back to the inline version.
>
> Needs the earlier patch to avoid lots of bogus warnings
> from objtool, but even with that there is one left.
>
> Fixes: 1dde7415e999 ("x86/retpoline: Simplify vmexit...")
> Signed-off-by: Andi Kleen <ak@linux.intel.com>

Instead of patch 1/2, the alternatives need to be annotated like:

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index af0ca73abb23..4deeb869ab83 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -89,6 +89,7 @@
.macro FILL_RETURN_BUFFER nr:req ftr:req
#ifdef CONFIG_RETPOLINE
ALTERNATIVE "", "call __clear_rsb" , \ftr
+ ANNOTATE_NOSPEC_ALTERNATIVE
ALTERNATIVE "", "STUFF_ONE_RSB", \ftr
#endif
.endm
@@ -178,7 +179,7 @@ extern char __indirect_thunk_end[];
static inline void vmexit_fill_RSB(void)
{
#ifdef CONFIG_RETPOLINE
- alternative_input("",
+ alternative_input(ANNOTATE_NOSPEC_ALTERNATIVE,
"call __fill_rsb;" STUFF_ONE_RSB,
X86_FEATURE_RETPOLINE,
ASM_NO_INPUT_CLOBBER(_ASM_BX, "memory"));
\
 
 \ /
  Last update: 2018-02-13 02:07    [W:0.097 / U:3.996 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site