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[2620:137:e000::1:20]) by mx.google.com with ESMTP id i4-20020a63cd04000000b0055c853ecc4dsi349443pgg.693.2023.08.02.08.07.34; Wed, 02 Aug 2023 08:07:57 -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=@linutronix.de header.s=2020 header.b=hfZeeLXW; dkim=neutral (no key) header.i=@linutronix.de header.s=2020e header.b="CVn1n/xy"; 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=QUARANTINE dis=NONE) header.from=linutronix.de Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232476AbjHBOd2 (ORCPT + 99 others); Wed, 2 Aug 2023 10:33:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36182 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232489AbjHBOdU (ORCPT ); Wed, 2 Aug 2023 10:33:20 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6798E19B0; Wed, 2 Aug 2023 07:33:18 -0700 (PDT) Date: Wed, 02 Aug 2023 14:33:15 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1690986796; 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=Pah/arar9NtcS7UbPidywH94kx8HEMnQMVyR6NuD98w=; b=hfZeeLXWDdBK/tWgk3Ft359Z3bpUifeYdtRXplcHkurCMqxHGRrERvAoDVkmQ9vxA87scb 0yr8gORFLfwjTeXcaGZrEfRLFagzz66XVVXWEVZPuRdnnBBsN6irL5gSG+fPYcWHMUAxyK PBdmWrKPhRekucd3zr61f1p0T/Z5o9fZK8RIodnJaRLoBYtlueHGiR+PQ99BsP/cpNl8Hj qCew/wVzGifg1z86hNAGe7AQN244CJarq2t79HOY1p07M3bX1iOKIR9+4hbjC1i7R/QRHI AEvRbOrhmBEJqlQ9yvHG44NexwYhW8n5DPtBxR2OinqLXbf/YStFhsQTrk5Z+w== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1690986796; 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=Pah/arar9NtcS7UbPidywH94kx8HEMnQMVyR6NuD98w=; b=CVn1n/xyCGLuxybIe8G+5w0u3iYNsRijvNrYrvHgsUxRqBjoWhD+zZn4n1B7QNw4ZvIfms XMODNHzBNYPh0ABQ== From: "tip-bot2 for Petr Pavlu" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: x86/core] x86/retpoline,kprobes: Skip optprobe check for indirect jumps with retpolines and IBT Cc: "Peter Zijlstra (Intel)" , "Masami Hiramatsu (Google)" , Petr Pavlu , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230711091952.27944-3-petr.pavlu@suse.com> References: <20230711091952.27944-3-petr.pavlu@suse.com> MIME-Version: 1.0 Message-ID: <169098679555.28540.9078901836593234321.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_BLOCKED, 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: INBOX X-GMAIL-THRID: 1771115884067835960 X-GMAIL-MSGID: 1773130353136673249 The following commit has been merged into the x86/core branch of tip: Commit-ID: 029239c5b0e6484e4443be90e5664fd0bf0f066b Gitweb: https://git.kernel.org/tip/029239c5b0e6484e4443be90e5664fd0bf0f066b Author: Petr Pavlu AuthorDate: Tue, 11 Jul 2023 11:19:52 +02:00 Committer: Peter Zijlstra CommitterDate: Wed, 02 Aug 2023 16:27:08 +02:00 x86/retpoline,kprobes: Skip optprobe check for indirect jumps with retpolines and IBT The kprobes optimization check can_optimize() calls insn_is_indirect_jump() to detect indirect jump instructions in a target function. If any is found, creating an optprobe is disallowed in the function because the jump could be from a jump table and could potentially land in the middle of the target optprobe. With retpolines, insn_is_indirect_jump() additionally looks for calls to indirect thunks which the compiler potentially used to replace original jumps. This extra check is however unnecessary because jump tables are disabled when the kernel is built with retpolines. The same is currently the case with IBT. Based on this observation, remove the logic to look for calls to indirect thunks and skip the check for indirect jumps altogether if the kernel is built with retpolines or IBT. Remove subsequently the symbols __indirect_thunk_start and __indirect_thunk_end which are no longer needed. Dropping this logic indirectly fixes a problem where the range [__indirect_thunk_start, __indirect_thunk_end] wrongly included also the return thunk. It caused that machines which used the return thunk as a mitigation and didn't have it patched by any alternative ended up not being able to use optprobes in any regular function. Fixes: 0b53c374b9ef ("x86/retpoline: Use -mfunction-return") Suggested-by: Peter Zijlstra (Intel) Suggested-by: Masami Hiramatsu (Google) Signed-off-by: Petr Pavlu Signed-off-by: Peter Zijlstra (Intel) Acked-by: Masami Hiramatsu (Google) Link: https://lore.kernel.org/r/20230711091952.27944-3-petr.pavlu@suse.com --- arch/x86/include/asm/nospec-branch.h | 3 +-- arch/x86/kernel/kprobes/opt.c | 40 ++++++++++----------------- arch/x86/kernel/vmlinux.lds.S | 2 +- tools/perf/util/thread-stack.c | 4 +--- 4 files changed, 17 insertions(+), 32 deletions(-) diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index 1a65cf4..db460e6 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -465,9 +465,6 @@ enum ssb_mitigation { SPEC_STORE_BYPASS_SECCOMP, }; -extern char __indirect_thunk_start[]; -extern char __indirect_thunk_end[]; - static __always_inline void alternative_msr_write(unsigned int msr, u64 val, unsigned int feature) { diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c index 57b0037..517821b 100644 --- a/arch/x86/kernel/kprobes/opt.c +++ b/arch/x86/kernel/kprobes/opt.c @@ -226,7 +226,7 @@ static int copy_optimized_instructions(u8 *dest, u8 *src, u8 *real) } /* Check whether insn is indirect jump */ -static int __insn_is_indirect_jump(struct insn *insn) +static int insn_is_indirect_jump(struct insn *insn) { return ((insn->opcode.bytes[0] == 0xff && (X86_MODRM_REG(insn->modrm.value) & 6) == 4) || /* Jump */ @@ -260,26 +260,6 @@ static int insn_jump_into_range(struct insn *insn, unsigned long start, int len) return (start <= target && target <= start + len); } -static int insn_is_indirect_jump(struct insn *insn) -{ - int ret = __insn_is_indirect_jump(insn); - -#ifdef CONFIG_RETPOLINE - /* - * Jump to x86_indirect_thunk_* is treated as an indirect jump. - * Note that even with CONFIG_RETPOLINE=y, the kernel compiled with - * older gcc may use indirect jump. So we add this check instead of - * replace indirect-jump check. - */ - if (!ret) - ret = insn_jump_into_range(insn, - (unsigned long)__indirect_thunk_start, - (unsigned long)__indirect_thunk_end - - (unsigned long)__indirect_thunk_start); -#endif - return ret; -} - /* Decode whole function to ensure any instructions don't jump into target */ static int can_optimize(unsigned long paddr) { @@ -334,9 +314,21 @@ static int can_optimize(unsigned long paddr) /* Recover address */ insn.kaddr = (void *)addr; insn.next_byte = (void *)(addr + insn.length); - /* Check any instructions don't jump into target */ - if (insn_is_indirect_jump(&insn) || - insn_jump_into_range(&insn, paddr + INT3_INSN_SIZE, + /* + * Check any instructions don't jump into target, indirectly or + * directly. + * + * The indirect case is present to handle a code with jump + * tables. When the kernel uses retpolines, the check should in + * theory additionally look for jumps to indirect thunks. + * However, the kernel built with retpolines or IBT has jump + * tables disabled so the check can be skipped altogether. + */ + if (!IS_ENABLED(CONFIG_RETPOLINE) && + !IS_ENABLED(CONFIG_X86_KERNEL_IBT) && + insn_is_indirect_jump(&insn)) + return 0; + if (insn_jump_into_range(&insn, paddr + INT3_INSN_SIZE, DISP32_SIZE)) return 0; addr += insn.length; diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index a4cd04c..dd5b0a6 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -133,9 +133,7 @@ SECTIONS KPROBES_TEXT SOFTIRQENTRY_TEXT #ifdef CONFIG_RETPOLINE - __indirect_thunk_start = .; *(.text..__x86.*) - __indirect_thunk_end = .; #endif STATIC_CALL_TEXT diff --git a/tools/perf/util/thread-stack.c b/tools/perf/util/thread-stack.c index 374d142..c6a0a27 100644 --- a/tools/perf/util/thread-stack.c +++ b/tools/perf/util/thread-stack.c @@ -1038,9 +1038,7 @@ static int thread_stack__trace_end(struct thread_stack *ts, static bool is_x86_retpoline(const char *name) { - const char *p = strstr(name, "__x86_indirect_thunk_"); - - return p == name || !strcmp(name, "__indirect_thunk_start"); + return strstr(name, "__x86_indirect_thunk_") == name; } /*