Commit-ID: 0795e94c2eacd888c88e2ad2321368b6b0fcb20a Gitweb: https://git.kernel.org/tip/0795e94c2eacd888c88e2ad2321368b6b0fcb20a Author: Borislav Petkov <[email protected]> AuthorDate: Wed, 10 Jan 2018 12:28:16 +0100 Committer: Thomas Gleixner <[email protected]> CommitDate: Wed, 10 Jan 2018 19:09:08 +0100
x86/alternatives: Fix optimize_nops() checking 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 <[email protected]> Signed-off-by: Borislav Petkov <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Cc: Tom Lendacky <[email protected]> Cc: Andi Kleen <[email protected]> Cc: Tim Chen <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Jiri Kosina <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Andi Kleen <[email protected]> Cc: Andrew Lutomirski <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Greg Kroah-Hartman <[email protected]> Cc: Paul Turner <[email protected]> Link: https://lkml.kernel.org/r/[email protected] --- 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 3344d33..e0b97e4 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -344,9 +344,12 @@ done: static void __init_or_module noinline 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);
