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[2620:137:e000::1:20]) by mx.google.com with ESMTP id l9-20020a170903120900b001aadb1147e4si9993356plh.456.2023.05.12.05.27.06; Fri, 12 May 2023 05:27:21 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@alien8.de header.s=dkim header.b=YsBQCgik; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=alien8.de Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240465AbjELMKJ (ORCPT + 99 others); Fri, 12 May 2023 08:10:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46196 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240619AbjELMKG (ORCPT ); Fri, 12 May 2023 08:10:06 -0400 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B14FA8A7F for ; Fri, 12 May 2023 05:10:02 -0700 (PDT) Received: from zn.tnic (p5de8e8ea.dip0.t-ipconnect.de [93.232.232.234]) (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 EF09D1EC06BB; Fri, 12 May 2023 14:10:00 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1683893401; 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=XXdDtIm5Yyh7u3GZFHc0giHYrBZnc+M+v0f931fOy68=; b=YsBQCgikQW7QGDYDoR4adEQdnRjPigqKP4zRPcsXEur8kVoVAsWyO25vbvPVCxe9hOcKKw z35rH5MJWsPuSS2Xug/Jh2QfehH2okYAGD1A3ueDVN0c9KoxKrVJtDKyLWzC4gPYZY1ts7 ZMRrbWU46nQUHRCkhfD2A5tY8pmMGw8= From: Borislav Petkov To: X86 ML Cc: LKML Subject: [PATCH] x86/alternative: Optimize returns patching Date: Fri, 12 May 2023 14:09:52 +0200 Message-Id: <20230512120952.7924-1-bp@alien8.de> X-Mailer: git-send-email 2.35.1 MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS, T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1765691297469163136?= X-GMAIL-MSGID: =?utf-8?q?1765691297469163136?= From: "Borislav Petkov (AMD)" Instead of decoding each instruction in the return sites range only to realize that that return site is a jump to the default return thunk which is needed - X86_FEATURE_RETHUNK is enabled - lift that check before the loop and get rid of that loop overhead. Add comments about what gets patched, while at it. Signed-off-by: Borislav Petkov (AMD) Acked-by: Peter Zijlstra (Intel) --- arch/x86/kernel/alternative.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index b78d55f0dfad..3bb0a5f61e8c 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -693,13 +693,12 @@ static int patch_return(void *addr, struct insn *insn, u8 *bytes) { int i = 0; + /* Patch the custom return thunks... */ if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) { - if (x86_return_thunk == __x86_return_thunk) - return -1; - i = JMP32_INSN_SIZE; __text_gen_insn(bytes, JMP32_INSN_OPCODE, addr, x86_return_thunk, i); } else { + /* ... or patch them out if not needed. */ bytes[i++] = RET_INSN_OPCODE; } @@ -712,6 +711,14 @@ void __init_or_module noinline apply_returns(s32 *start, s32 *end) { s32 *s; + /* + * Do not patch out the default return thunks if those needed are the + * ones generated by the compiler. + */ + if (cpu_feature_enabled(X86_FEATURE_RETHUNK) && + (x86_return_thunk == __x86_return_thunk)) + return; + for (s = start; s < end; s++) { void *dest = NULL, *addr = (void *)s + *s; struct insn insn;