iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

x86/nospec: Fix i386 RSB stuffing

Browse Source 
commit 332924973725e8cdcc783c175f68cf7e162cb9e5 upstream.

Turns out that i386 doesn't unconditionally have LFENCE, as such the
loop in __FILL_RETURN_BUFFER isn't actually speculation safe on such
chips.

Fixes: ba6e31af2be9 ("x86/speculation: Add LFENCE to RSB fill sequence")
Reported-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/Yv9tj9vbQ9nNlXoY@worktop.programming.kicks-ass.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Zijlstra 2022-08-19 13:01:35 +02:00 committed by Greg Kroah-Hartman
parent 7b0163c1b0
commit b864bc2ad4
1 changed files with 12 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
arch/x86/include/asm/nospec-branch.h
View File

@ -50,6 +50,7 @@
* the optimal version - two calls, each with their own speculation
* trap should their return address end up getting used, in a loop.
*/
#ifdef CONFIG_X86_64
#define __FILL_RETURN_BUFFER(reg, nr) \
mov $(nr/2), reg; \
771: \
@ -60,6 +61,17 @@
jnz 771b; \
/* barrier for jnz misprediction */ \
lfence;
#else
/*
* i386 doesn't unconditionally have LFENCE, as such it can't
* do a loop.
*/
#define __FILL_RETURN_BUFFER(reg, nr) \
.rept nr; \
__FILL_RETURN_SLOT; \
.endr; \
add $(BITS_PER_LONG/8) * nr, %_ASM_SP;
#endif
/*
* Stuff a single RSB slot.