From: Peter Zijlstra peterz@infradead.org
commit 09d09531a51a24635bc3331f56d92ee7092f5516 upstream.
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 Signed-off-by: Suraj Jitindar Singh surajjs@amazon.com Cc: stable@vger.kernel.org # 5.10.x --- arch/x86/include/asm/nospec-branch.h | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index ce5e6e70d2a4..3434e5ebd3c7 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -118,6 +118,19 @@ #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 @@ -125,19 +138,18 @@ */ .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