The patch titled Subject: x86/traps: move kmsan check after instrumentation_begin has been added to the -mm mm-hotfixes-unstable branch. Its filename is x86-traps-move-kmsan-check-after-instrumentation_begin.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Sabyrzhan Tasbolatov snovitoll@gmail.com Subject: x86/traps: move kmsan check after instrumentation_begin Date: Wed, 16 Oct 2024 20:24:07 +0500

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(-)

--- a/arch/x86/kernel/traps.c~x86-traps-move-kmsan-check-after-instrumentation_begin +++ a/arch/x86/kernel/traps.c @@ -261,12 +261,6 @@ static noinstr bool handle_bug(struct pt 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; @@ -276,6 +270,12 @@ static noinstr bool handle_bug(struct pt */ 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. */ _

Patches currently in -mm which might be from snovitoll@gmail.com are

x86-traps-move-kmsan-check-after-instrumentation_begin.patch mm-kasan-kmsan-copy_from-to_kernel_nofault.patch