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x86: Use return-thunk in asm code

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Use the return thunk in asm code. If the thunk isn't needed, it will
get patched into a RET instruction during boot by apply_returns().

Since alternatives can't handle relocations outside of the first
instruction, putting a 'jmp __x86_return_thunk' in one is not valid,
therefore carve out the memmove ERMS path into a separate label and jump
to it.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
This commit is contained in:
Peter Zijlstra 2022-06-14 23:15:45 +02:00 • committed by Borislav Petkov
parent 0ee9073000
commit aa3d480315
3 changed files with 15 additions and 1 deletions
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1
arch/x86/entry/vdso/Makefile
View file

@ -92,6 +92,7 @@ endif
endif
$(vobjs): KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO) $(RANDSTRUCT_CFLAGS) $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
$(vobjs): KBUILD_AFLAGS += -DBUILD_VDSO
#
# vDSO code runs in userspace and -pg doesn't help with profiling anyway.

8
arch/x86/include/asm/linkage.h
View file

@ -19,19 +19,27 @@
#define __ALIGN_STR __stringify(__ALIGN)
#endif
#if defined(CONFIG_RETPOLINE) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO)
#define RET jmp __x86_return_thunk
#else /* CONFIG_RETPOLINE */
#ifdef CONFIG_SLS
#define RET ret; int3
#else
#define RET ret
#endif
#endif /* CONFIG_RETPOLINE */
#else /* __ASSEMBLY__ */
#if defined(CONFIG_RETPOLINE) && !defined(__DISABLE_EXPORTS) && !defined(BUILD_VDSO)
#define ASM_RET "jmp __x86_return_thunk\n\t"
#else /* CONFIG_RETPOLINE */
#ifdef CONFIG_SLS
#define ASM_RET "ret; int3\n\t"
#else
#define ASM_RET "ret\n\t"
#endif
#endif /* CONFIG_RETPOLINE */
#endif /* __ASSEMBLY__ */

7
arch/x86/lib/memmove_64.S
View file

@ -39,7 +39,7 @@ SYM_FUNC_START(__memmove)
/* FSRM implies ERMS => no length checks, do the copy directly */
.Lmemmove_begin_forward:
ALTERNATIVE "cmp $0x20, %rdx; jb 1f", "", X86_FEATURE_FSRM
ALTERNATIVE "", __stringify(movq %rdx, %rcx; rep movsb; RET), X86_FEATURE_ERMS
ALTERNATIVE "", "jmp .Lmemmove_erms", X86_FEATURE_ERMS
/*
* movsq instruction have many startup latency
@ -205,6 +205,11 @@ SYM_FUNC_START(__memmove)
movb %r11b, (%rdi)
13:
RET
.Lmemmove_erms:
movq %rdx, %rcx
rep movsb
RET
SYM_FUNC_END(__memmove)
EXPORT_SYMBOL(__memmove)