From patchwork Wed Jan 24 07:40:45 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Pawan Gupta X-Patchwork-Id: 13528714 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.7]) (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 433A2171D4; Wed, 24 Jan 2024 07:40:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.7 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706082050; cv=none; b=mTb9cbEAV6zk19XM9RV2UuIfmyKTh4JWrTIgoD0bqL4cMSVLmO0Fn2eaR7hVzOZxQmgQS8qcsP0Kz+Nr/0q0gBdUBcmZoiRXJ9LBjwuuG5VSCQs2pWRGYzpXM2E3f32ORxPkoZ2DUStm5WhLWCCrXhJqUck+2rTqcNfhtfaOi8s= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706082050; c=relaxed/simple; bh=sf3/J3TxNecVxaGlT19PfvywBeZ3eGQX4HZ0By+XnhM=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition; b=Ja0lxxYxXrJj2T4zxsEVIcrvH7KHxhrFb2qBEGiB2TYfFJFbackhoSpc5Jr5etNYmPyruTxkiT85caFv+uxgEUIFju93aRkHyLF5QWgn5ta7wCRKwzl+acej73bATjua8gmU02aVLTNVl2b3lweSTzSq64qgGQtZy1agEuVoxZo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=none smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=FLgjF7G0; arc=none smtp.client-ip=192.198.163.7 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="FLgjF7G0" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1706082049; x=1737618049; h=date:from:to:cc:subject:message-id:mime-version; bh=sf3/J3TxNecVxaGlT19PfvywBeZ3eGQX4HZ0By+XnhM=; b=FLgjF7G059HKxnAi5YwQ5ZYcPT6wgN8vbmqyItFcpT2GJpfEZu8FAtpQ sBLx9yy/K0JBmS7/pXSaoj4Ph2f9DzXR30knI5cEHBTo9BFCxSLWV5mGn 9dOUSudsiEaQ9j2X/eGKZ1l6dWv7xNNongovCat1VKD+mZii/22STWNkq Evz8SDNZe9JfTZ9iEjaOZBglqp8mumTaPyKkoOkUmpLIl9d1Rbmko6C5x qXl0R3tA06GvoOpEkVuUhWL6fM4NzmOTEdMfZlLBKgPJLuYUW+Yt6aZtD S5u9ulYpbGcX4xpY4y8S9/KQfmkoS/KeyMi9vIQKYLvdBt2mCjiaOCaUX w==; X-IronPort-AV: E=McAfee;i="6600,9927,10962"; a="23230798" X-IronPort-AV: E=Sophos;i="6.05,216,1701158400"; d="scan'208";a="23230798" Received: from orviesa005.jf.intel.com ([10.64.159.145]) by fmvoesa101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Jan 2024 23:40:47 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.05,216,1701158400"; d="scan'208";a="1790942" Received: from bbaidya-mobl.amr.corp.intel.com (HELO desk) ([10.209.53.134]) by orviesa005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Jan 2024 23:40:46 -0800 Date: Tue, 23 Jan 2024 23:40:45 -0800 From: Pawan Gupta To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Peter Zijlstra , Josh Poimboeuf , Andy Lutomirski , Jonathan Corbet , Sean Christopherson , Paolo Bonzini , tony.luck@intel.com, ak@linux.intel.com, tim.c.chen@linux.intel.com, Andrew Cooper , Nikolay Borisov Cc: linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, Alyssa Milburn , Daniel Sneddon , antonio.gomez.iglesias@linux.intel.com, Pawan Gupta , Alyssa Milburn , Dave Hansen Subject: [PATCH v6 0/6] Delay VERW Message-ID: <20240123-delay-verw-v6-0-a8206baca7d3@linux.intel.com> X-B4-Tracking: v=1; b=H4sIAHC9sGUC/23QQQ6CMBQE0KuQri1p/28LuPIexgWWjzRBMAWrx nB3G4wJRJYzybzFvNlA3tHA9smbeQpucH0Xg9klzDZldyHuqpgZCEAppOQVteWLB/IPXgmVqSI 3Z7DI4uDmqXbPGTsydopN44ax969ZD3LuvxCIJRQkF9zWtVaiMAimOrSuuz9T143Upra/zliAJ aBWAESglnkuUQmbi2wbwCWgVwBGQIMxaLKMCPU2oH+Ailesvgg6AiWeAVWBSKX5B6Zp+gBnnA3 SbwEAAA== X-Mailer: b4 0.12.3 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline v6: - Simplify FB_CLEAR checks in vmx_update_fb_clear_dis() and the comment. (Sean) v5: https://lore.kernel.org/r/20240111-delay-verw-v5-0-a3b234933ea6@linux.intel.com - Added comment to SYM_CODE_START_NOALIGN(mds_verw_sel) explaining VERW operand is in code segment so that VERW at works with KPTI. (Josh/Borislav). - Fixed changelog for patch 1/6. (Borislav) - Clarify CLEAR_CPU_BUFFERS macro documentation. (Josh) - KVM: Move the check to skip FB_CLEAR_CTRL optimization for guests when X86_FEATURE_CLEAR_CPU_BUF is set. (Josh) - Rebased to v6.7 v4: https://lore.kernel.org/all/20231027-delay-verw-v4-0-9a3622d4bcf7@linux.intel.com/ - Fill unused part of mds_verw_sel cacheline with int3. (Andrew) - Fix the formatting in documentation (0-day). - s/inspite/in spite/ (Sean). - Explicitly skip FB_CLEAR optimization when MDS affected (Sean). v3: https://lore.kernel.org/r/20231025-delay-verw-v3-0-52663677ee35@linux.intel.com - Use .entry.text section for VERW memory operand. (Andrew/PeterZ) - Fix the duplicate header inclusion. (Chao) v2: https://lore.kernel.org/r/20231024-delay-verw-v2-0-f1881340c807@linux.intel.com - Removed the extra EXEC_VERW macro layers. (Sean) - Move NOPL before VERW. (Sean) - s/USER_CLEAR_CPU_BUFFERS/CLEAR_CPU_BUFFERS/. (Josh/Dave) - Removed the comments before CLEAR_CPU_BUFFERS. (Josh) - Remove CLEAR_CPU_BUFFERS from NMI returning to kernel and document the reason. (Josh/Dave) - Reformat comment in md_clear_update_mitigation(). (Josh) - Squash "x86/bugs: Cleanup mds_user_clear" patch. (Nikolay) - s/GUEST_CLEAR_CPU_BUFFERS/CLEAR_CPU_BUFFERS/. (Josh) - Added a patch from Sean to use CFLAGS.CF for VMLAUNCH/VMRESUME selection. This facilitates a single CLEAR_CPU_BUFFERS location for both VMLAUNCH and VMRESUME. (Sean) v1: https://lore.kernel.org/r/20231020-delay-verw-v1-0-cff54096326d@linux.intel.com Hi, Legacy instruction VERW was overloaded by some processors to clear micro-architectural CPU buffers as a mitigation of CPU bugs. This series moves VERW execution to a later point in exit-to-user path. This is needed because in some cases it may be possible for kernel data to be accessed after VERW in arch_exit_to_user_mode(). Such accesses may put data into MDS affected CPU buffers, for example: 1. Kernel data accessed by an NMI between VERW and return-to-user can remain in CPU buffers (since NMI returning to kernel does not execute VERW to clear CPU buffers). 2. Alyssa reported that after VERW is executed, CONFIG_GCC_PLUGIN_STACKLEAK=y scrubs the stack used by a system call. Memory accesses during stack scrubbing can move kernel stack contents into CPU buffers. 3. When caller saved registers are restored after a return from function executing VERW, the kernel stack accesses can remain in CPU buffers(since they occur after VERW). Although these cases are less practical to exploit, moving VERW closer to ring transition reduces the attack surface. Overview of the series: Patch 1: Prepares VERW macros for use in asm. Patch 2: Adds macros to 64-bit entry/exit points. Patch 3: Adds macros to 32-bit entry/exit points. Patch 4: Enables the new macros. Patch 5: Uses CFLAGS.CF for VMLAUNCH/VMRESUME selection. Patch 6: Adds macro to VMenter. Below is some performance data collected on a Skylake client compared with previous implementation: Baseline: v6.6-rc5 | Test | Configuration | v1 | v3 | | ------------------ | ---------------------- | ---- | ---- | | build-linux-kernel | defconfig | 1.00 | 1.00 | | hackbench | 32 - Process | 1.02 | 1.06 | | nginx | Short Connection - 500 | 1.01 | 1.04 | Cc: linux-kernel@vger.kernel.org Cc: linux-doc@vger.kernel.org Cc: kvm@vger.kernel.org Cc: Alyssa Milburn Cc: Daniel Sneddon Cc: antonio.gomez.iglesias@linux.intel.com To: Thomas Gleixner To: Ingo Molnar To: Borislav Petkov To: Dave Hansen To: x86@kernel.org To: "H. Peter Anvin" To: Peter Zijlstra To: Josh Poimboeuf To: Andy Lutomirski To: Jonathan Corbet To: Sean Christopherson To: Paolo Bonzini To: tony.luck@intel.com To: ak@linux.intel.com To: tim.c.chen@linux.intel.com To: Andrew Cooper To: Nikolay Borisov Signed-off-by: Pawan Gupta --- Pawan Gupta (5): x86/bugs: Add asm helpers for executing VERW x86/entry_64: Add VERW just before userspace transition x86/entry_32: Add VERW just before userspace transition x86/bugs: Use ALTERNATIVE() instead of mds_user_clear static key KVM: VMX: Move VERW closer to VMentry for MDS mitigation Sean Christopherson (1): KVM: VMX: Use BT+JNC, i.e. EFLAGS.CF to select VMRESUME vs. VMLAUNCH Documentation/arch/x86/mds.rst | 38 +++++++++++++++++++++++++----------- arch/x86/entry/entry.S | 22 +++++++++++++++++++++ arch/x86/entry/entry_32.S | 3 +++ arch/x86/entry/entry_64.S | 11 +++++++++++ arch/x86/entry/entry_64_compat.S | 1 + arch/x86/include/asm/cpufeatures.h | 2 +- arch/x86/include/asm/entry-common.h | 1 - arch/x86/include/asm/nospec-branch.h | 27 +++++++++++++------------ arch/x86/kernel/cpu/bugs.c | 15 ++++++-------- arch/x86/kernel/nmi.c | 3 --- arch/x86/kvm/vmx/run_flags.h | 7 +++++-- arch/x86/kvm/vmx/vmenter.S | 9 ++++++--- arch/x86/kvm/vmx/vmx.c | 20 +++++++++++++++---- 13 files changed, 113 insertions(+), 46 deletions(-) --- base-commit: 0dd3ee31125508cd67f7e7172247f05b7fd1753a change-id: 20231011-delay-verw-d0474986b2c3 Best regards,