From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B67E44CA784; Wed, 30 Sep 2026 16:57:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790787467; cv=none; b=bqBTKeA8jV9TTH77ex1QvXx2Nvrf7iLp4oIBm7Q+H6Ay5WdtMCzawxTa47BrUqoOvJGON9/R3WUYK9ezRIxrbFU0bWHAU2MMbHxvbEiJAYZtGRJYHgHe5NigRG3UaY6rFsZJapwX4dMHext/+mJaPHANi+jT4ymJw8+H9ad3Fvs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790787467; c=relaxed/simple; bh=807k00g4c5MkDeHV9inEFF5pAxL0YwpL89GxaFVOmTw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=VGyNCVZXTVJr2c2AeQug+hF/wGMBrD1mRrRoZLso4W3eKeZPlnp7Fi5MRCm6vnwulSjMvQVKEi3WcrFXBSwFn6pLh45nLoFMcEgY6WneSLqan6RRAO38N4CigFXZsjJROKibQa6ZgH9hshVQtsJBFbbowSY29kdoaQsfHksJ3bY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=mD4buwSM; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="mD4buwSM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1B2BB1F000FF; Wed, 30 Sep 2026 16:57:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1790787465; bh=LsUe9DHBxvP5/qL+VV0tRzLXLlgSv7sb+HM7W7mQIF8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=mD4buwSM+f1toDbqJqMTlITKCGs2hP1DK4dlvGpUr1FuSXcFmWEgk9zExnAcFcMy/ Lio/u9pGX1HF1GOoUraX8sikLiuzNfQNxSNsanwzgVqcqW4PGQ3kBMf8WGJo12RTvV 4dWWRBWQt9T9958LDpiqtUloWQ9VsE+kBAQdYKl0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Masami Hiramatsu (Google)" , "Borislav Petkov (AMD)" , "Peter Zijlstra (Intel)" , stable@kernel.org Subject: [PATCH 7.2 239/457] x86/mce: Fix hardware debug register corruption on task migration Date: Wed, 30 Sep 2026 17:25:44 +0200 Message-ID: <20260930152351.201566815@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260930152346.024115587@linuxfoundation.org> References: <20260930152346.024115587@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Masami Hiramatsu (Google) commit b8d1d5b63a8ef532038eebd9d97d406860385668 upstream. In exc_machine_check_user(), local_db_save() and local_db_restore() are invoked in the outer entry stubs (DEFINE_IDTENTRY_MCE_USER, DEFINE_FREDENTRY_MCE, and DEFINE_IDTENTRY_RAW), surrounding exc_machine_check_user(). However, exc_machine_check_user() calls irqentry_exit_to_user_mode(), which handles pending thread work and may schedule() if TIF_NEED_RESCHED is set. If the task migrates to another CPU during schedule(), local_db_restore() runs on the new CPU with the dr7 state saved from the old CPU. This corrupts the new CPU's DR7 hardware debug register and leaves the old CPU's DR7 disabled. In short, local_db_save() and local_db_restore() pair must be run on the same CPU. To fix this, move local_db_save() and local_db_restore() inside exc_machine_check_user() and exc_machine_check_kernel(). In exc_machine_check_user(), DR7 is saved and restored strictly around do_machine_check() to avoid schedule() during migration. In exc_machine_check_kernel(), local_db_save() is called at the entry point to prevent early memory accesses from triggering nested #DB exceptions, and restored on all exits. Fixes: cd840e424f27 ("x86/entry, mce: Disallow #DB during #MC") Assisted-by: LLM Signed-off-by: Masami Hiramatsu (Google) Signed-off-by: Borislav Petkov (AMD) Acked-by: Peter Zijlstra (Intel) Cc: Link: https://patch.msgid.link/179005109564.388919.3937970081044095776.stgit@devnote2 Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/cpu/mce/core.c | 27 ++++++++++----------------- 1 file changed, 10 insertions(+), 17 deletions(-) --- a/arch/x86/kernel/cpu/mce/core.c +++ b/arch/x86/kernel/cpu/mce/core.c @@ -2108,6 +2108,9 @@ bool filter_mce(struct mce *m) static __always_inline void exc_machine_check_kernel(struct pt_regs *regs) { irqentry_state_t irq_state; + unsigned long dr7; + + dr7 = local_db_save(); WARN_ON_ONCE(user_mode(regs)); @@ -2116,20 +2119,26 @@ static __always_inline void exc_machine_ * mce_check_crashing_cpu() for details. */ if (mca_cfg.initialized && mce_check_crashing_cpu()) - return; + goto out; irq_state = irqentry_nmi_enter(regs); do_machine_check(regs); irqentry_nmi_exit(regs, irq_state); +out: + local_db_restore(dr7); } static __always_inline void exc_machine_check_user(struct pt_regs *regs) { + unsigned long dr7; + irqentry_enter_from_user_mode(regs); + dr7 = local_db_save(); do_machine_check(regs); + local_db_restore(dr7); irqentry_exit_to_user_mode(regs); } @@ -2138,21 +2147,13 @@ static __always_inline void exc_machine_ /* MCE hit kernel mode */ DEFINE_IDTENTRY_MCE(exc_machine_check) { - unsigned long dr7; - - dr7 = local_db_save(); exc_machine_check_kernel(regs); - local_db_restore(dr7); } /* The user mode variant. */ DEFINE_IDTENTRY_MCE_USER(exc_machine_check) { - unsigned long dr7; - - dr7 = local_db_save(); exc_machine_check_user(regs); - local_db_restore(dr7); } #ifdef CONFIG_X86_FRED @@ -2169,28 +2170,20 @@ DEFINE_IDTENTRY_MCE_USER(exc_machine_che */ DEFINE_FREDENTRY_MCE(exc_machine_check) { - unsigned long dr7; - - dr7 = local_db_save(); if (user_mode(regs)) exc_machine_check_user(regs); else exc_machine_check_kernel(regs); - local_db_restore(dr7); } #endif #else /* 32bit unified entry point */ DEFINE_IDTENTRY_RAW(exc_machine_check) { - unsigned long dr7; - - dr7 = local_db_save(); if (user_mode(regs)) exc_machine_check_user(regs); else exc_machine_check_kernel(regs); - local_db_restore(dr7); } #endif