From 1154bbd326de4453858cf78cf29420888b3ffd52 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Mon, 24 Mar 2025 14:55:54 -0700 Subject: objtool: Fix X86_FEATURE_SMAP alternative handling For X86_FEATURE_SMAP alternatives which replace NOP with STAC or CLAC, uaccess validation skips the NOP branch to avoid following impossible code paths, e.g. where a STAC would be patched but a CLAC wouldn't. However, it's not safe to assume an X86_FEATURE_SMAP alternative is patching STAC/CLAC. There can be other alternatives, like static_cpu_has(), where both branches need to be validated. Fix that by repurposing ANNOTATE_IGNORE_ALTERNATIVE for skipping either original instructions or new ones. This is a more generic approach which enables the removal of the feature checking hacks and the insn->ignore bit. Fixes the following warnings: arch/x86/mm/fault.o: warning: objtool: do_user_addr_fault+0x8ec: __stack_chk_fail() missing __noreturn in .c/.h or NORETURN() in noreturns.h arch/x86/mm/fault.o: warning: objtool: do_user_addr_fault+0x8f1: unreachable instruction [ mingo: Fix up conflicts with recent x86 changes. ] Fixes: ea24213d8088 ("objtool: Add UACCESS validation") Reported-by: kernel test robot Signed-off-by: Josh Poimboeuf Signed-off-by: Ingo Molnar Cc: Linus Torvalds Link: https://lore.kernel.org/r/de0621ca242130156a55d5d74fed86994dfa4c9c.1742852846.git.jpoimboe@kernel.org Closes: https://lore.kernel.org/oe-kbuild-all/202503181736.zkZUBv4N-lkp@intel.com/ --- arch/x86/include/asm/arch_hweight.h | 6 ++++-- arch/x86/include/asm/smap.h | 23 +++++++++++++++-------- arch/x86/include/asm/xen/hypercall.h | 6 ++---- 3 files changed, 21 insertions(+), 14 deletions(-) (limited to 'arch/x86') diff --git a/arch/x86/include/asm/arch_hweight.h b/arch/x86/include/asm/arch_hweight.h index b5982b94bdba..cbc6157f0b4b 100644 --- a/arch/x86/include/asm/arch_hweight.h +++ b/arch/x86/include/asm/arch_hweight.h @@ -16,7 +16,8 @@ static __always_inline unsigned int __arch_hweight32(unsigned int w) { unsigned int res; - asm_inline (ALTERNATIVE("call __sw_hweight32", + asm_inline (ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE + "call __sw_hweight32", "popcntl %[val], %[cnt]", X86_FEATURE_POPCNT) : [cnt] "=" REG_OUT (res), ASM_CALL_CONSTRAINT : [val] REG_IN (w)); @@ -45,7 +46,8 @@ static __always_inline unsigned long __arch_hweight64(__u64 w) { unsigned long res; - asm_inline (ALTERNATIVE("call __sw_hweight64", + asm_inline (ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE + "call __sw_hweight64", "popcntq %[val], %[cnt]", X86_FEATURE_POPCNT) : [cnt] "=" REG_OUT (res), ASM_CALL_CONSTRAINT : [val] REG_IN (w)); diff --git a/arch/x86/include/asm/smap.h b/arch/x86/include/asm/smap.h index daea94c2993c..55a5e656e4b9 100644 --- a/arch/x86/include/asm/smap.h +++ b/arch/x86/include/asm/smap.h @@ -16,23 +16,23 @@ #ifdef __ASSEMBLER__ #define ASM_CLAC \ - ALTERNATIVE "", "clac", X86_FEATURE_SMAP + ALTERNATIVE __stringify(ANNOTATE_IGNORE_ALTERNATIVE), "clac", X86_FEATURE_SMAP #define ASM_STAC \ - ALTERNATIVE "", "stac", X86_FEATURE_SMAP + ALTERNATIVE __stringify(ANNOTATE_IGNORE_ALTERNATIVE), "stac", X86_FEATURE_SMAP #else /* __ASSEMBLER__ */ static __always_inline void clac(void) { /* Note: a barrier is implicit in alternative() */ - alternative("", "clac", X86_FEATURE_SMAP); + alternative(ANNOTATE_IGNORE_ALTERNATIVE "", "clac", X86_FEATURE_SMAP); } static __always_inline void stac(void) { /* Note: a barrier is implicit in alternative() */ - alternative("", "stac", X86_FEATURE_SMAP); + alternative(ANNOTATE_IGNORE_ALTERNATIVE "", "stac", X86_FEATURE_SMAP); } static __always_inline unsigned long smap_save(void) @@ -40,7 +40,8 @@ static __always_inline unsigned long smap_save(void) unsigned long flags; asm volatile ("# smap_save\n\t" - ALTERNATIVE("", "pushf; pop %0; " "clac" "\n\t", + ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE + "", "pushf; pop %0; clac", X86_FEATURE_SMAP) : "=rm" (flags) : : "memory", "cc"); @@ -50,16 +51,22 @@ static __always_inline unsigned long smap_save(void) static __always_inline void smap_restore(unsigned long flags) { asm volatile ("# smap_restore\n\t" - ALTERNATIVE("", "push %0; popf\n\t", + ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE + "", "push %0; popf", X86_FEATURE_SMAP) : : "g" (flags) : "memory", "cc"); } /* These macros can be used in asm() statements */ #define ASM_CLAC \ - ALTERNATIVE("", "clac", X86_FEATURE_SMAP) + ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE "", "clac", X86_FEATURE_SMAP) #define ASM_STAC \ - ALTERNATIVE("", "stac", X86_FEATURE_SMAP) + ALTERNATIVE(ANNOTATE_IGNORE_ALTERNATIVE "", "stac", X86_FEATURE_SMAP) + +#define ASM_CLAC_UNSAFE \ + ALTERNATIVE("", ANNOTATE_IGNORE_ALTERNATIVE "clac", X86_FEATURE_SMAP) +#define ASM_STAC_UNSAFE \ + ALTERNATIVE("", ANNOTATE_IGNORE_ALTERNATIVE "stac", X86_FEATURE_SMAP) #endif /* __ASSEMBLER__ */ diff --git a/arch/x86/include/asm/xen/hypercall.h b/arch/x86/include/asm/xen/hypercall.h index 97771b9d33af..59a62c3780a2 100644 --- a/arch/x86/include/asm/xen/hypercall.h +++ b/arch/x86/include/asm/xen/hypercall.h @@ -231,14 +231,12 @@ static __always_inline void __xen_stac(void) * Suppress objtool seeing the STAC/CLAC and getting confused about it * calling random code with AC=1. */ - asm volatile(ANNOTATE_IGNORE_ALTERNATIVE - ASM_STAC ::: "memory", "flags"); + asm volatile(ASM_STAC_UNSAFE ::: "memory", "flags"); } static __always_inline void __xen_clac(void) { - asm volatile(ANNOTATE_IGNORE_ALTERNATIVE - ASM_CLAC ::: "memory", "flags"); + asm volatile(ASM_CLAC_UNSAFE ::: "memory", "flags"); } static inline long -- cgit v1.2.3