| From 612e8e9350fd19cae6900cf36ea0c6892d1a0dca Mon Sep 17 00:00:00 2001 |
| From: Borislav Petkov <bp@suse.de> |
| Date: Wed, 10 Jan 2018 12:28:16 +0100 |
| Subject: x86/alternatives: Fix optimize_nops() checking |
| |
| From: Borislav Petkov <bp@suse.de> |
| |
| 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 <dwmw2@infradead.org> |
| Signed-off-by: Borislav Petkov <bp@suse.de> |
| Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
| Cc: Tom Lendacky <thomas.lendacky@amd.com> |
| Cc: Andi Kleen <ak@linux.intel.com> |
| Cc: Tim Chen <tim.c.chen@linux.intel.com> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Cc: Jiri Kosina <jikos@kernel.org> |
| Cc: Dave Hansen <dave.hansen@intel.com> |
| Cc: Andi Kleen <andi@firstfloor.org> |
| Cc: Andrew Lutomirski <luto@kernel.org> |
| Cc: Linus Torvalds <torvalds@linux-foundation.org> |
| Cc: Greg Kroah-Hartman <gregkh@linux-foundation.org> |
| Cc: Paul Turner <pjt@google.com> |
| Link: https://lkml.kernel.org/r/20180110112815.mgciyf5acwacphkq@pd.tnic |
| Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| arch/x86/kernel/alternative.c | 7 +++++-- |
| 1 file changed, 5 insertions(+), 2 deletions(-) |
| |
| --- a/arch/x86/kernel/alternative.c |
| +++ b/arch/x86/kernel/alternative.c |
| @@ -340,9 +340,12 @@ done: |
| 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); |
