The patch below does not apply to the v6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
Thanks, Sasha
------------------ original commit in Linus's tree ------------------
From 1db272864ff250b5e607283eaec819e1186c8e26 Mon Sep 17 00:00:00 2001 From: Sabyrzhan Tasbolatov snovitoll@gmail.com Date: Wed, 16 Oct 2024 20:24:07 +0500 Subject: [PATCH] x86/traps: move kmsan check after instrumentation_begin
During x86_64 kernel build with CONFIG_KMSAN, the objtool warns following:
AR built-in.a AR vmlinux.a LD vmlinux.o vmlinux.o: warning: objtool: handle_bug+0x4: call to kmsan_unpoison_entry_regs() leaves .noinstr.text section OBJCOPY modules.builtin.modinfo GEN modules.builtin MODPOST Module.symvers CC .vmlinux.export.o
Moving kmsan_unpoison_entry_regs() _after_ instrumentation_begin() fixes the warning.
There is decode_bug(regs->ip, &imm) is left before KMSAN unpoisoining, but it has the return condition and if we include it after instrumentation_begin() it results the warning "return with instrumentation enabled", hence, I'm concerned that regs will not be KMSAN unpoisoned if `ud_type == BUG_NONE` is true.
Link: https://lkml.kernel.org/r/20241016152407.3149001-1-snovitoll@gmail.com Fixes: ba54d194f8da ("x86/traps: avoid KMSAN bugs originating from handle_bug()") Signed-off-by: Sabyrzhan Tasbolatov snovitoll@gmail.com Reviewed-by: Alexander Potapenko glider@google.com Cc: Borislav Petkov (AMD) bp@alien8.de Cc: Dave Hansen dave.hansen@linux.intel.com Cc: Ingo Molnar mingo@redhat.com Cc: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org --- arch/x86/kernel/traps.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index d05392db5d0fe..2dbadf347b5f4 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -261,12 +261,6 @@ static noinstr bool handle_bug(struct pt_regs *regs) int ud_type; u32 imm;
- /* - * Normally @regs are unpoisoned by irqentry_enter(), but handle_bug() - * is a rare case that uses @regs without passing them to - * irqentry_enter(). - */ - kmsan_unpoison_entry_regs(regs); ud_type = decode_bug(regs->ip, &imm); if (ud_type == BUG_NONE) return handled; @@ -275,6 +269,12 @@ static noinstr bool handle_bug(struct pt_regs *regs) * All lies, just get the WARN/BUG out. */ instrumentation_begin(); + /* + * Normally @regs are unpoisoned by irqentry_enter(), but handle_bug() + * is a rare case that uses @regs without passing them to + * irqentry_enter(). + */ + kmsan_unpoison_entry_regs(regs); /* * Since we're emulating a CALL with exceptions, restore the interrupt * state to what it was at the exception site.