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

x86,nospec: Simplify {JMP,CALL}_NOSPEC

Browse Source 
Have {JMP,CALL}_NOSPEC generate the same code GCC does for indirect
calls and rely on the objtool retpoline patching infrastructure.

There's no reason these should be alternatives while the vast bulk of
compiler generated retpolines are not.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
This commit is contained in:
Peter Zijlstra 2022-07-20 12:04:21 +02:00
parent ff6992735a
commit 09d09531a5
1 changed files with 18 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
arch/x86/include/asm/nospec-branch.h
View File

@ -93,6 +93,19 @@
#endif
.endm
/*
* Equivalent to -mindirect-branch-cs-prefix; emit the 5 byte jmp/call
* to the retpoline thunk with a CS prefix when the register requires
* a RAX prefix byte to encode. Also see apply_retpolines().
*/
.macro __CS_PREFIX reg:req
.irp rs,r8,r9,r10,r11,r12,r13,r14,r15
.ifc \reg,\rs
.byte 0x2e
.endif
.endr
.endm
/*
* JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple
* indirect jmp/call which may be susceptible to the Spectre variant 2
@ -100,19 +113,18 @@
*/
.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
__CS_PREFIX \reg
jmp __x86_indirect_thunk_\reg
#else
jmp *%\reg
int3
#endif
.endm
.macro CALL_NOSPEC reg:req
#ifdef CONFIG_RETPOLINE
ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg), \
__stringify(call __x86_indirect_thunk_\reg), X86_FEATURE_RETPOLINE, \
__stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *%\reg), X86_FEATURE_RETPOLINE_LFENCE
__CS_PREFIX \reg
call __x86_indirect_thunk_\reg
#else
call *%\reg
#endif