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=-20.8 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,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS 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 C5FB1C47098 for ; Thu, 3 Jun 2021 14:38:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AF36A613BA for ; Thu, 3 Jun 2021 14:38:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231612AbhFCOkN (ORCPT ); Thu, 3 Jun 2021 10:40:13 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:46910 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229744AbhFCOkK (ORCPT ); Thu, 3 Jun 2021 10:40:10 -0400 Date: Thu, 03 Jun 2021 14:38:23 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1622731104; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=sm2ggrAef4nSUjwqaeqwSUsiU9l5NxvixZEowSXC6xY=; b=M6O8j3CkD/GLOrbRvkV29Bjf0SIXoEcsfPgpET5/bWhMlwfK8NdXi4jQjjk4fAE4o46KR0 bU37tdGOrhNl9Q/gjPg+CWb2rXylGShtZdScllLTUhjDGb1TqRQ/82XBkSdRzv/ZY/04pr pI+GxW6yJbXJWYa2yzCfATeSjLtqEc5W2QfiZcP/TGU6szRJst/Hh2eVHVKq5PAQqul+fC tCYb1/3B7FyU37H5Gk/8jgsI9tTUu6q1p4SPOUMfGQZibEH7vN5clOUIzT+ILERu0mo0Ni g2tD1HuTRmmWb4qyvyzSX71diR8ATtGooFo+2NfyV0WxXPVhmxKEr3FbYLxaBw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1622731104; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=sm2ggrAef4nSUjwqaeqwSUsiU9l5NxvixZEowSXC6xY=; b=BEM5Vnd0cwWJhyu+0q6Zp7IPVj5ekok6uiv/rE8Ge/tckyy9hrIztevBrptCYBSS6sJFHW SFeRxgea7qHacCCw== From: "tip-bot2 for Borislav Petkov" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: x86/urgent] x86/alternative: Optimize single-byte NOPs at an arbitrary position Cc: Richard Narron , Borislav Petkov , "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20210601212125.17145-1-bp@alien8.de> References: <20210601212125.17145-1-bp@alien8.de> MIME-Version: 1.0 Message-ID: <162273110395.29796.14379457953065896336.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the x86/urgent branch of tip: Commit-ID: 2b31e8ed96b260ce2c22bd62ecbb9458399e3b62 Gitweb: https://git.kernel.org/tip/2b31e8ed96b260ce2c22bd62ecbb9458399e3b62 Author: Borislav Petkov AuthorDate: Tue, 01 Jun 2021 17:51:22 +02:00 Committer: Borislav Petkov CommitterDate: Thu, 03 Jun 2021 16:33:09 +02:00 x86/alternative: Optimize single-byte NOPs at an arbitrary position 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 Signed-off-by: Borislav Petkov Acked-by: Peter Zijlstra (Intel) Link: https://bugzilla.kernel.org/show_bug.cgi?id=213301 Link: https://lkml.kernel.org/r/20210601212125.17145-1-bp@alien8.de --- arch/x86/kernel/alternative.c | 64 ++++++++++++++++++++++++---------- 1 file changed, 46 insertions(+), 18 deletions(-) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 6974b51..6fe5b44 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -183,41 +183,69 @@ done: } /* + * optimize_nops_range() - Optimize a sequence of single byte NOPs (0x90) + * + * @instr: instruction byte stream + * @instrlen: length of the above + * @off: offset within @instr where the first NOP has been detected + * + * Return: number of NOPs found (and replaced). + */ +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); } /*