From 1ac5fc23c160f82956aa23fd595206a15d80d742 Mon Sep 17 00:00:00 2001 From: Borislav Petkov Date: Wed, 10 Jan 2018 12:28:16 +0100 Subject: [PATCH 059/103] x86/alternatives: Fix optimize_nops() checking commit 612e8e9350fd19cae6900cf36ea0c6892d1a0dca upstream. The alternatives code checks only the first byte whether it is a NOP, but with NOPs in front of the payload and having actual instructions after it breaks the "optimized' test. Make sure to scan all bytes before deciding to optimize the NOPs in there. Reported-by: David Woodhouse Signed-off-by: Borislav Petkov Signed-off-by: Thomas Gleixner Cc: Tom Lendacky Cc: Andi Kleen Cc: Tim Chen Cc: Peter Zijlstra Cc: Jiri Kosina Cc: Dave Hansen Cc: Andi Kleen Cc: Andrew Lutomirski Cc: Linus Torvalds Cc: Greg Kroah-Hartman Cc: Paul Turner Link: https://lkml.kernel.org/r/20180110112815.mgciyf5acwacphkq@pd.tnic Signed-off-by: David Woodhouse Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/alternative.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 5cb272a..10d5a3d 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -340,9 +340,12 @@ recompute_jump(struct alt_instr *a, u8 *orig_insn, u8 *repl_insn, u8 *insnbuf) static void __init_or_module optimize_nops(struct alt_instr *a, u8 *instr) { unsigned long flags; + int i; - if (instr[0] != 0x90) - return; + for (i = 0; i < a->padlen; i++) { + if (instr[i] != 0x90) + return; + } local_irq_save(flags); add_nops(instr + (a->instrlen - a->padlen), a->padlen); -- 2.7.4