From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966472AbbBCSRH (ORCPT ); Tue, 3 Feb 2015 13:17:07 -0500 Received: from mail.skyhub.de ([78.46.96.112]:60138 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756092AbbBCSQ5 (ORCPT ); Tue, 3 Feb 2015 13:16:57 -0500 From: Borislav Petkov To: X86 ML Cc: LKML Subject: [PATCH v1 05/12] x86, alternatives: Use optimized NOPs for padding Date: Tue, 3 Feb 2015 19:16:23 +0100 Message-Id: <1422987390-17878-6-git-send-email-bp@alien8.de> X-Mailer: git-send-email 2.2.0.33.gc18b867 In-Reply-To: <1422987390-17878-1-git-send-email-bp@alien8.de> References: <1422987390-17878-1-git-send-email-bp@alien8.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Borislav Petkov Alternatives allow now for 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. Signed-off-by: Borislav Petkov --- arch/x86/kernel/alternative.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 715af37bf008..dd0cdb6b179c 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -323,6 +323,21 @@ done: n_dspl, (unsigned long)orig_insn + n_dspl + repl_len); } +static void __init_or_module optimize_nops(u8 *instr, u8 max_len) +{ + int i = 0; + + while (instr[i] == 0x90 && i < max_len) + i++; + + if (!i) + return; + + add_nops(instr, i); + + DUMP_BYTES(instr, i, "%p: optimized NOPs: ", instr); +} + /* * 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 +369,11 @@ 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 (instr[0] == 0x90) + optimize_nops(instr, a->instrlen); continue; + } DPRINTK("feat: %d*32+%d, old: (%p, len: %d), repl: (%p, len: %d)", a->cpuid >> 5, -- 2.2.0.33.gc18b867