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x86/ibt: Make cfi_bhi a constant for FINEIBT_BHI=n

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Robot yielded a .config that tripped:

  vmlinux.o: warning: objtool: do_jit+0x276: relocation to !ENDBR: .noinstr.text+0x6a60

This is the result of using __bhi_args[1] in unreachable code; make
sure the compiler is able to determine this is unreachable and trigger
DCE.

Closes: https://lore.kernel.org/oe-kbuild-all/202503030704.H9KFysNS-lkp@intel.com/
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250303094911.GL5880@noisy.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2025-03-03 10:21:47 +01:00
parent dfebe7362f
commit 73e8079be9
2 changed files with 12 additions and 0 deletions
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5
arch/x86/include/asm/cfi.h
View file

@ -100,7 +100,12 @@ enum cfi_mode {
};
extern enum cfi_mode cfi_mode;
#ifdef CONFIG_FINEIBT_BHI
extern bool cfi_bhi;
#else
#define cfi_bhi (0)
#endif
typedef u8 bhi_thunk[32];
extern bhi_thunk __bhi_args[];

7
arch/x86/kernel/alternative.c
View file

@ -936,7 +936,10 @@ void __init_or_module apply_seal_endbr(s32 *start, s32 *end) { }
#endif
enum cfi_mode cfi_mode __ro_after_init = __CFI_DEFAULT;
#ifdef CONFIG_FINEIBT_BHI
bool cfi_bhi __ro_after_init = false;
#endif
#ifdef CONFIG_CFI_CLANG
struct bpf_insn;
@ -1070,11 +1073,15 @@ static __init int cfi_parse_cmdline(char *str)
pr_err("Ignoring paranoid; depends on fineibt.\n");
}
} else if (!strcmp(str, "bhi")) {
#ifdef CONFIG_FINEIBT_BHI
if (cfi_mode == CFI_FINEIBT) {
cfi_bhi = true;
} else {
pr_err("Ignoring bhi; depends on fineibt.\n");
}
#else
pr_err("Ignoring bhi; depends on FINEIBT_BHI=y.\n");
#endif
} else {
pr_err("Ignoring unknown cfi option (%s).", str);
}