From 4fd4b6e5537cec5b56db0b22546dd439ebb26830 Mon Sep 17 00:00:00 2001 From: Borislav Petkov Date: Sat, 10 Jan 2015 20:34:07 +0100 Subject: [PATCH] x86/alternatives: Use optimized NOPs for padding Alternatives allow now for an empty old instruction. In this case we go and pad the space with NOPs at assembly time. However, there are the optimal, longer NOPs which should be used. Do that at patching time by adding alt_instr.padlen-sized NOPs at the old instruction address. Cc: Andy Lutomirski Signed-off-by: Borislav Petkov --- arch/x86/kernel/alternative.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 715af37..af397cc 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -323,6 +323,14 @@ done: n_dspl, (unsigned long)orig_insn + n_dspl + repl_len); } +static void __init_or_module optimize_nops(struct alt_instr *a, u8 *instr) +{ + add_nops(instr + (a->instrlen - a->padlen), a->padlen); + + DUMP_BYTES(instr, a->instrlen, "%p: [%d:%d) optimized NOPs: ", + instr, a->instrlen - a->padlen, a->padlen); +} + /* * Replace instructions with better alternatives for this CPU type. This runs * before SMP is initialized to avoid SMP problems with self modifying code. @@ -354,8 +362,12 @@ void __init_or_module apply_alternatives(struct alt_instr *start, replacement = (u8 *)&a->repl_offset + a->repl_offset; BUG_ON(a->instrlen > sizeof(insnbuf)); BUG_ON(a->cpuid >= (NCAPINTS + NBUGINTS) * 32); - if (!boot_cpu_has(a->cpuid)) + if (!boot_cpu_has(a->cpuid)) { + if (a->padlen > 1) + optimize_nops(a, instr); + continue; + } DPRINTK("feat: %d*32+%d, old: (%p, len: %d), repl: (%p, len: %d)", a->cpuid >> 5, -- 2.7.4