From: Borislav Petkov <[email protected]> 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 <[email protected]> Signed-off-by: Borislav Petkov <[email protected]> --- 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 715af37bf008..af397cc98d05 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, -- 2.2.0.33.gc18b867 -- 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/
