4.14-stable review patch. If anyone has any objections, please let me know.
------------------
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: 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 @@ -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);