[tip: x86/core] x86/traps: Clarify KCFI instruction layout

[tip: x86/core] x86/traps: Clarify KCFI instruction layout

[tip-bot2 for Kees Cook]

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     628a15e0536abb7658cd243553312d3f65c0aff2
Gitweb:        https://git.kernel.org/tip/628a15e0536abb7658cd243553312d3f65c0aff2
Author:        Kees Cook <kees@kernel.org>
AuthorDate:    Wed, 03 Sep 2025 20:46:41 -07:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 04 Sep 2025 21:59:07 +02:00

x86/traps: Clarify KCFI instruction layout

Just a nit-picky change to the KCFI indirect call check instruction
documentation. The addl offset isn't always -4 (it depends on patchable
function entry configuration).

Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250904034656.3670313-2-kees@kernel.org
---
 arch/x86/kernel/cfi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cfi.c b/arch/x86/kernel/cfi.c
index 77086cf..638eb5c 100644
--- a/arch/x86/kernel/cfi.c
+++ b/arch/x86/kernel/cfi.c
@@ -27,7 +27,7 @@ static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target,
 	 * for indirect call checks:
 	 *
 	 *   movl    -<id>, %r10d       ; 6 bytes
-	 *   addl    -4(%reg), %r10d    ; 4 bytes
+	 *   addl    -<pos>(%reg), %r10d; 4 bytes
 	 *   je      .Ltmp1             ; 2 bytes
 	 *   ud2                        ; <- regs->ip
 	 *   .Ltmp1: