From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4AAA2C4708F for ; Tue, 1 Jun 2021 21:21:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1E98A610CB for ; Tue, 1 Jun 2021 21:21:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234863AbhFAVXW (ORCPT ); Tue, 1 Jun 2021 17:23:22 -0400 Received: from mail.skyhub.de ([5.9.137.197]:51488 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234831AbhFAVXT (ORCPT ); Tue, 1 Jun 2021 17:23:19 -0400 Received: from zn.tnic (p200300ec2f111d0093004df6f0d27e9c.dip0.t-ipconnect.de [IPv6:2003:ec:2f11:1d00:9300:4df6:f0d2:7e9c]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 6ED551EC0288; Tue, 1 Jun 2021 23:21:36 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1622582496; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type: content-transfer-encoding:content-transfer-encoding:in-reply-to: references; bh=r6po77ash8nSd+/o4Au/rz1P1mxTHjT+9nnkvAgn8+E=; b=gOd/30Z5BByE+u0vlUXbN52jkEJnKTUBSmsGP2OxydiPFFMWs8t0TthCLECUr9iNFgSv2c Fhd02cwuAGPtgSUi7FE/z91xSAQ/Krby7bEmMANlsdFsIHGZytNg+otQJ/KG3PXm4fi56m fZl7B7Tg+51iR/FAllP36J5Ib8UnecM= From: Borislav Petkov To: X86 ML Cc: LKML , Richard Narron Subject: [PATCH] x86/alternative: Optimize single-byte NOPs at an arbitrary position Date: Tue, 1 Jun 2021 23:21:25 +0200 Message-Id: <20210601212125.17145-1-bp@alien8.de> X-Mailer: git-send-email 2.29.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Borislav Petkov Up until now the assumption was that an alternative patching site would have some instructions at the beginning and trailing single-byte NOPs (0x90) padding. Therefore, the patching machinery would go and optimize those single-byte NOPs into longer ones. However, this assumption is broken on 32-bit when code like hv_do_hypercall() in hyperv_init() would use the ratpoline speculation killer CALL_NOSPEC. The 32-bit version of that macro would align certain insns to 16 bytes, leading to the compiler issuing a one or more single-byte NOPs, depending on the holes it needs to fill for alignment. That would lead to the warning in optimize_nops() to fire: ------------[ cut here ]------------ Not a NOP at 0xc27fb598 WARNING: CPU: 0 PID: 0 at arch/x86/kernel/alternative.c:211 optimize_nops.isra.13 due to that function verifying whether all of the following bytes really are single-byte NOPs. Therefore, carve out the NOP padding into a separate function and call it for each NOP range beginning with a single-byte NOP. Fixes: 23c1ad538f4f ("x86/alternatives: Optimize optimize_nops()") Reported-by: Richard Narron Link: https://bugzilla.kernel.org/show_bug.cgi?id=213301 Signed-off-by: Borislav Petkov --- arch/x86/kernel/alternative.c | 62 +++++++++++++++++++++++++---------- 1 file changed, 44 insertions(+), 18 deletions(-) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 6974b5174495..7baf13b11952 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -182,42 +182,68 @@ recompute_jump(struct alt_instr *a, u8 *orig_insn, u8 *repl_insn, u8 *insn_buff) n_dspl, (unsigned long)orig_insn + n_dspl + repl_len); } +/* + * @instr: instruction byte stream + * @instrlen: length of the above + * @off: offset within @instr where the first NOP has been detected + */ +static __always_inline int optimize_nops_range(u8 *instr, u8 instrlen, int off) +{ + unsigned long flags; + int i = off, nnops; + + while (i < instrlen) { + if (instr[i] != 0x90) + break; + + i++; + } + + nnops = i - off; + + if (nnops <= 1) + return nnops; + + local_irq_save(flags); + add_nops(instr + off, nnops); + local_irq_restore(flags); + + DUMP_BYTES(instr, instrlen, "%px: [%d:%d) optimized NOPs: ", + instr, off, i); + + return nnops; +} + + /* * "noinline" to cause control flow change and thus invalidate I$ and * cause refetch after modification. */ static void __init_or_module noinline optimize_nops(struct alt_instr *a, u8 *instr) { - unsigned long flags; struct insn insn; - int nop, i = 0; + int i = 0; /* - * Jump over the non-NOP insns, the remaining bytes must be single-byte - * NOPs, optimize them. + * Jump over the non-NOP insns and optimize single-byte NOPs into bigger + * ones. */ for (;;) { if (insn_decode_kernel(&insn, &instr[i])) return; + /* + * See if this and any potentially following NOPs can be + * optimized. + */ if (insn.length == 1 && insn.opcode.bytes[0] == 0x90) - break; - - if ((i += insn.length) >= a->instrlen) - return; - } + i += optimize_nops_range(instr, a->instrlen, i); + else + i += insn.length; - for (nop = i; i < a->instrlen; i++) { - if (WARN_ONCE(instr[i] != 0x90, "Not a NOP at 0x%px\n", &instr[i])) + if (i >= a->instrlen) return; } - - local_irq_save(flags); - add_nops(instr + nop, i - nop); - local_irq_restore(flags); - - DUMP_BYTES(instr, a->instrlen, "%px: [%d:%d) optimized NOPs: ", - instr, nop, a->instrlen); } /* -- 2.29.2