From 2bd4aa9325821551648cf9738d6aa3a49317d7e5 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 14 Jun 2023 16:35:50 +0200 Subject: [PATCH] x86/alternative: PAUSE is not a NOP While chasing ghosts, I did notice that optimize_nops() was replacing 'REP NOP' aka 'PAUSE' with NOP2. This is clearly not right. Fixes: 6c480f222128 ("x86/alternative: Rewrite optimize_nops() some") Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/linux-next/20230524130104.GR83892@hirez.programming.kicks-ass.net/ --- arch/x86/kernel/alternative.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index bbfbf7ad..a7e1ec5 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -169,9 +169,12 @@ void text_poke_early(void *addr, const void *opcode, size_t len); */ static bool insn_is_nop(struct insn *insn) { - if (insn->opcode.bytes[0] == 0x90) + /* Anything NOP, but no REP NOP */ + if (insn->opcode.bytes[0] == 0x90 && + (!insn->prefixes.nbytes || insn->prefixes.bytes[0] != 0xF3)) return true; + /* NOPL */ if (insn->opcode.bytes[0] == 0x0F && insn->opcode.bytes[1] == 0x1F) return true; -- 2.7.4