From: Borislav Petkov <[email protected]> Take a look at the first insn byte before optimizing the NOP - there might be something else already, like the ALTERNATIVE_2() in rdtsc_barrier() which nops out on AMD even though we just patched in an MFENCE.
This happens because the alternatives sees X86_FEATURE_MFENCE_RDTSC, AMD CPUs set it, we patch in the MFENCE and right afterwards it sees X86_FEATURE_LFENCE_RDTSC which AMD CPUs don't set and we blindly optimize the NOP. Checking whether at least the first byte is 0x90 prevents that. Signed-off-by: Borislav Petkov <[email protected]> --- arch/x86/kernel/alternative.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 7c4ad005d7a0..aef653193160 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -325,6 +325,9 @@ done: static void __init_or_module optimize_nops(struct alt_instr *a, u8 *instr) { + if (instr[0] != 0x90) + return; + add_nops(instr + (a->instrlen - a->padlen), a->padlen); DUMP_BYTES(instr, a->instrlen, "%p: [%d:%d) optimized NOPs: ", -- 2.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
