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x86/retpoline: Use -mfunction-return
commit 0b53c374b9
upstream.
Utilize -mfunction-return=thunk-extern when available to have the
compiler replace RET instructions with direct JMPs to the symbol
__x86_return_thunk. This does not affect assembler (.S) sources, only C
sources.
-mfunction-return=thunk-extern has been available since gcc 7.3 and
clang 15.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
[cascardo: RETPOLINE_CFLAGS is at Makefile]
[cascardo: remove ANNOTATE_NOENDBR from __x86_return_thunk]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
parent
023123a619
commit
7e70d9c050
3 changed files with 16 additions and 0 deletions
2
Makefile
2
Makefile
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@ -687,11 +687,13 @@ endif
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ifdef CONFIG_CC_IS_GCC
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RETPOLINE_CFLAGS := $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register)
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RETPOLINE_CFLAGS += $(call cc-option,-mfunction-return=thunk-extern)
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RETPOLINE_VDSO_CFLAGS := $(call cc-option,-mindirect-branch=thunk-inline -mindirect-branch-register)
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endif
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ifdef CONFIG_CC_IS_CLANG
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RETPOLINE_CFLAGS := -mretpoline-external-thunk
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RETPOLINE_VDSO_CFLAGS := -mretpoline
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RETPOLINE_CFLAGS += $(call cc-option,-mfunction-return=thunk-extern)
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endif
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export RETPOLINE_CFLAGS
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export RETPOLINE_VDSO_CFLAGS
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@ -120,6 +120,8 @@
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_ASM_PTR " 999b\n\t" \
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".popsection\n\t"
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extern void __x86_return_thunk(void);
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#ifdef CONFIG_RETPOLINE
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typedef u8 retpoline_thunk_t[RETPOLINE_THUNK_SIZE];
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@ -66,3 +66,15 @@ SYM_CODE_END(__x86_indirect_thunk_array)
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#define GEN(reg) EXPORT_THUNK(reg)
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#include <asm/GEN-for-each-reg.h>
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#undef GEN
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/*
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* This function name is magical and is used by -mfunction-return=thunk-extern
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* for the compiler to generate JMPs to it.
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*/
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SYM_CODE_START(__x86_return_thunk)
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UNWIND_HINT_EMPTY
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ret
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int3
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SYM_CODE_END(__x86_return_thunk)
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__EXPORT_THUNK(__x86_return_thunk)
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