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x86/bug: Add printf() validation to HAVE_ARCH_BUG_FORMAT_ARGS WARNs

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Add explicit printf() validation for x86-64's newfangled WARN
implementation, as most (all?) compilers fail to detect basic formatting
issues without the annotation.  E.g. even goofs like printing a u64 as a
string aren't detected:

  WARN_ONCE(1, "Bad message, %s", vcpu->arch.last_guest_tsc);

32-bit x86 doesn't support HAVE_ARCH_BUG_FORMAT_ARGS and uses generic
implementations that provide printf() validation. This means there's
now a big blind spot is code that is strictly x86-64. Inconveniently,
new features are also frequently x86-64-only.

Fix the blind 64-bit blind spot.

[ dhansen: changelog tweaks to flesh out the 64-bit-only details ]

Fixes: 5b472b6e5b ("x86_64/bug: Implement __WARN_printf()")
Fixes: 11bb4944f0 ("x86/bug: Implement WARN_ONCE()")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/all/adc1IrD8uqWdaOKv@yzhao56-desk.sh.intel.com
Link: https://patch.msgid.link/20260423145419.459988-2-seanjc@google.com
This commit is contained in:
Sean Christopherson 2026-04-23 07:54:17 -07:00 committed by Dave Hansen
parent 254f49634e
commit 40c4b47f41
1 changed files with 2 additions and 0 deletions
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2
arch/x86/include/asm/bug.h
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@ -153,6 +153,7 @@ struct arch_va_list {
struct sysv_va_list args;
};
extern void *__warn_args(struct arch_va_list *args, struct pt_regs *regs);
static __always_inline __printf(1, 2) void __WARN_validate_printf(const char *fmt, ...) { }
#endif /* __ASSEMBLER__ */
#define __WARN_bug_entry(flags, format) ({ \
@ -172,6 +173,7 @@ extern void *__warn_args(struct arch_va_list *args, struct pt_regs *regs);
#define __WARN_print_arg(flags, format, arg...) \
do { \
int __flags = (flags) | BUGFLAG_WARNING | BUGFLAG_ARGS ; \
__WARN_validate_printf(format, ## arg); \
static_call_mod(WARN_trap)(__WARN_bug_entry(__flags, format), ## arg); \
asm (""); /* inhibit tail-call optimization */ \
} while (0)