From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (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 0149E2D791 for ; Thu, 26 Oct 2023 13:58:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=citrix.com header.i=@citrix.com header.b="OmRaJlt3" Received: from mail-ej1-x631.google.com (mail-ej1-x631.google.com [IPv6:2a00:1450:4864:20::631]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B1AE21A2 for ; Thu, 26 Oct 2023 06:58:44 -0700 (PDT) Received: by mail-ej1-x631.google.com with SMTP id a640c23a62f3a-9c41e95efcbso137588366b.3 for ; Thu, 26 Oct 2023 06:58:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=google; t=1698328723; x=1698933523; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:autocrypt:references:cc:to :content-language:subject:from:user-agent:mime-version:date :message-id:from:to:cc:subject:date:message-id:reply-to; bh=f/KYa4HkxjjRaaNse5zZEBCRtWEDy9TvEZNCSQroKlA=; b=OmRaJlt3h3pl7MI6mS0dHtDwDLhFscUlKG/I0p2L14uNCUXYP/uIiNVS/IIb54VzlQ rtVbLQQgM17vGASinGX+XKUpbfkmM4PXahpGGWAchVQanhNIxYYpjE3bIXyxI9Dy1fSw YiKeKr7EgiUWPQproy/AtMTfecv+3Gffgp+XI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1698328723; x=1698933523; h=content-transfer-encoding:in-reply-to:autocrypt:references:cc:to :content-language:subject:from:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=f/KYa4HkxjjRaaNse5zZEBCRtWEDy9TvEZNCSQroKlA=; b=uqkcFl73rDbm1GSgEjCyPMsyQmcx0N+PzEA8J94YOtiuiWR3fBaBsvzcV8QdIjXTsY 87nEM/bIthVvo5oxyz3mHX/gil6a6CmCMimDxiCNrPfpy8zGppzH7fpcJC7Dic3gcHGD LUX3e1ddMVMQTDFfKJheawF0YsRbK2UIRWEBI9a/V4FuapFpIiuf48hCua4cI5nND//n 5EWEyHaFQrDwzZG56KuSh2DSFerWiYjygDR/rMIOjXlgH5ixfrGm8uIrPWCLDZVRXC4J zBY+YSdhRtir6DmVtjVpc9XoSyZgJ07lIKnE7zC8QdDf4fXqj+N4hnqjsuk7rLNODBZc 8w/Q== X-Gm-Message-State: AOJu0Yyyp/2xPWjo39LVXxqriYxww/wQbzNS4SXLC8gAw13W7kNGcrhe pvBbICVXB4aTPzUwf7vyiKtrRA== X-Google-Smtp-Source: AGHT+IF2rU6imsm+9/5fNEkBUbTI0NVZdVoGckX2Pddx8Q6ImRaSm5Kbk4+MvlMi/u+iolhDKI4lYA== X-Received: by 2002:a17:907:70a:b0:9b8:b683:5854 with SMTP id xb10-20020a170907070a00b009b8b6835854mr15025269ejb.61.1698328723124; Thu, 26 Oct 2023 06:58:43 -0700 (PDT) Received: from [10.80.67.28] (default-46-102-197-194.interdsl.co.uk. [46.102.197.194]) by smtp.gmail.com with ESMTPSA id bm11-20020a170906c04b00b009a193a5acffsm11621069ejb.121.2023.10.26.06.58.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 26 Oct 2023 06:58:42 -0700 (PDT) Message-ID: <37b334b2-c040-458d-9c1f-2546dc9b378d@citrix.com> Date: Thu, 26 Oct 2023 14:58:41 +0100 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Andrew Cooper Subject: Re: [PATCH v3 1/6] x86/bugs: Add asm helpers for executing VERW Content-Language: en-GB To: Nikolay Borisov , Pawan Gupta , 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 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, Alyssa Milburn References: <20231025-delay-verw-v3-0-52663677ee35@linux.intel.com> <20231025-delay-verw-v3-1-52663677ee35@linux.intel.com> <1f756579-8f33-40ca-ae50-4db78c615f60@suse.com> Autocrypt: addr=andrew.cooper3@citrix.com; keydata= xsFNBFLhNn8BEADVhE+Hb8i0GV6mihnnr/uiQQdPF8kUoFzCOPXkf7jQ5sLYeJa0cQi6Penp VtiFYznTairnVsN5J+ujSTIb+OlMSJUWV4opS7WVNnxHbFTPYZVQ3erv7NKc2iVizCRZ2Kxn srM1oPXWRic8BIAdYOKOloF2300SL/bIpeD+x7h3w9B/qez7nOin5NzkxgFoaUeIal12pXSR Q354FKFoy6Vh96gc4VRqte3jw8mPuJQpfws+Pb+swvSf/i1q1+1I4jsRQQh2m6OTADHIqg2E ofTYAEh7R5HfPx0EXoEDMdRjOeKn8+vvkAwhviWXTHlG3R1QkbE5M/oywnZ83udJmi+lxjJ5 YhQ5IzomvJ16H0Bq+TLyVLO/VRksp1VR9HxCzItLNCS8PdpYYz5TC204ViycobYU65WMpzWe LFAGn8jSS25XIpqv0Y9k87dLbctKKA14Ifw2kq5OIVu2FuX+3i446JOa2vpCI9GcjCzi3oHV e00bzYiHMIl0FICrNJU0Kjho8pdo0m2uxkn6SYEpogAy9pnatUlO+erL4LqFUO7GXSdBRbw5 gNt25XTLdSFuZtMxkY3tq8MFss5QnjhehCVPEpE6y9ZjI4XB8ad1G4oBHVGK5LMsvg22PfMJ ISWFSHoF/B5+lHkCKWkFxZ0gZn33ju5n6/FOdEx4B8cMJt+cWwARAQABzSlBbmRyZXcgQ29v cGVyIDxhbmRyZXcuY29vcGVyM0BjaXRyaXguY29tPsLBegQTAQgAJAIbAwULCQgHAwUVCgkI CwUWAgMBAAIeAQIXgAUCWKD95wIZAQAKCRBlw/kGpdefoHbdD/9AIoR3k6fKl+RFiFpyAhvO 59ttDFI7nIAnlYngev2XUR3acFElJATHSDO0ju+hqWqAb8kVijXLops0gOfqt3VPZq9cuHlh IMDquatGLzAadfFx2eQYIYT+FYuMoPZy/aTUazmJIDVxP7L383grjIkn+7tAv+qeDfE+txL4 SAm1UHNvmdfgL2/lcmL3xRh7sub3nJilM93RWX1Pe5LBSDXO45uzCGEdst6uSlzYR/MEr+5Z JQQ32JV64zwvf/aKaagSQSQMYNX9JFgfZ3TKWC1KJQbX5ssoX/5hNLqxMcZV3TN7kU8I3kjK mPec9+1nECOjjJSO/h4P0sBZyIUGfguwzhEeGf4sMCuSEM4xjCnwiBwftR17sr0spYcOpqET ZGcAmyYcNjy6CYadNCnfR40vhhWuCfNCBzWnUW0lFoo12wb0YnzoOLjvfD6OL3JjIUJNOmJy RCsJ5IA/Iz33RhSVRmROu+TztwuThClw63g7+hoyewv7BemKyuU6FTVhjjW+XUWmS/FzknSi dAG+insr0746cTPpSkGl3KAXeWDGJzve7/SBBfyznWCMGaf8E2P1oOdIZRxHgWj0zNr1+ooF /PzgLPiCI4OMUttTlEKChgbUTQ+5o0P080JojqfXwbPAyumbaYcQNiH1/xYbJdOFSiBv9rpt TQTBLzDKXok86M7BTQRS4TZ/ARAAkgqudHsp+hd82UVkvgnlqZjzz2vyrYfz7bkPtXaGb9H4 Rfo7mQsEQavEBdWWjbga6eMnDqtu+FC+qeTGYebToxEyp2lKDSoAsvt8w82tIlP/EbmRbDVn 7bhjBlfRcFjVYw8uVDPptT0TV47vpoCVkTwcyb6OltJrvg/QzV9f07DJswuda1JH3/qvYu0p vjPnYvCq4NsqY2XSdAJ02HrdYPFtNyPEntu1n1KK+gJrstjtw7KsZ4ygXYrsm/oCBiVW/OgU g/XIlGErkrxe4vQvJyVwg6YH653YTX5hLLUEL1NS4TCo47RP+wi6y+TnuAL36UtK/uFyEuPy wwrDVcC4cIFhYSfsO0BumEI65yu7a8aHbGfq2lW251UcoU48Z27ZUUZd2Dr6O/n8poQHbaTd 6bJJSjzGGHZVbRP9UQ3lkmkmc0+XCHmj5WhwNNYjgbbmML7y0fsJT5RgvefAIFfHBg7fTY/i kBEimoUsTEQz+N4hbKwo1hULfVxDJStE4sbPhjbsPCrlXf6W9CxSyQ0qmZ2bXsLQYRj2xqd1 bpA+1o1j2N4/au1R/uSiUFjewJdT/LX1EklKDcQwpk06Af/N7VZtSfEJeRV04unbsKVXWZAk uAJyDDKN99ziC0Wz5kcPyVD1HNf8bgaqGDzrv3TfYjwqayRFcMf7xJaL9xXedMcAEQEAAcLB XwQYAQgACQUCUuE2fwIbDAAKCRBlw/kGpdefoG4XEACD1Qf/er8EA7g23HMxYWd3FXHThrVQ HgiGdk5Yh632vjOm9L4sd/GCEACVQKjsu98e8o3ysitFlznEns5EAAXEbITrgKWXDDUWGYxd pnjj2u+GkVdsOAGk0kxczX6s+VRBhpbBI2PWnOsRJgU2n10PZ3mZD4Xu9kU2IXYmuW+e5KCA vTArRUdCrAtIa1k01sPipPPw6dfxx2e5asy21YOytzxuWFfJTGnVxZZSCyLUO83sh6OZhJkk b9rxL9wPmpN/t2IPaEKoAc0FTQZS36wAMOXkBh24PQ9gaLJvfPKpNzGD8XWR5HHF0NLIJhgg 4ZlEXQ2fVp3XrtocHqhu4UZR4koCijgB8sB7Tb0GCpwK+C4UePdFLfhKyRdSXuvY3AHJd4CP 4JzW0Bzq/WXY3XMOzUTYApGQpnUpdOmuQSfpV9MQO+/jo7r6yPbxT7CwRS5dcQPzUiuHLK9i nvjREdh84qycnx0/6dDroYhp0DFv4udxuAvt1h4wGwTPRQZerSm4xaYegEFusyhbZrI0U9tJ B8WrhBLXDiYlyJT6zOV2yZFuW47VrLsjYnHwn27hmxTC/7tvG3euCklmkn9Sl9IAKFu29RSo d5bD8kMSCYsTqtTfT6W4A3qHGvIDta3ptLYpIAOD2sY3GYq2nf3Bbzx81wZK14JdDDHUX2Rs 6+ahAA== In-Reply-To: <1f756579-8f33-40ca-ae50-4db78c615f60@suse.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 26/10/2023 2:44 pm, Nikolay Borisov wrote: > > > >> + >> +.pushsection .entry.text, "ax" >> + >> +.align L1_CACHE_BYTES, 0xcc >> +SYM_CODE_START_NOALIGN(mds_verw_sel) >> +    UNWIND_HINT_UNDEFINED >> +    ANNOTATE_NOENDBR >> +    .word __KERNEL_DS >> +SYM_CODE_END(mds_verw_sel); >> +/* For KVM */ >> +EXPORT_SYMBOL_GPL(mds_verw_sel); >> + >> +.popsection > > > >> diff --git a/arch/x86/include/asm/nospec-branch.h >> b/arch/x86/include/asm/nospec-branch.h >> index c55cc243592e..005e69f93115 100644 >> --- a/arch/x86/include/asm/nospec-branch.h >> +++ b/arch/x86/include/asm/nospec-branch.h >> @@ -329,6 +329,21 @@ >>   #endif >>   .endm >>   +/* >> + * Macros to execute VERW instruction that mitigate transient data >> sampling >> + * attacks such as MDS. On affected systems a microcode update >> overloaded VERW >> + * instruction to also clear the CPU buffers. VERW clobbers CFLAGS.ZF. >> + * >> + * Note: Only the memory operand variant of VERW clears the CPU >> buffers. >> + */ >> +.macro EXEC_VERW >> +    verw _ASM_RIP(mds_verw_sel) >> +.endm >> + >> +.macro CLEAR_CPU_BUFFERS >> +    ALTERNATIVE "", __stringify(EXEC_VERW), X86_FEATURE_CLEAR_CPU_BUF >> +.endm > > > What happened with the first 5 bytes of a 7 byte nop being > complemented by __KERNEL_DS in order to handle VERW being executed > after user registers are restored and having its memory operand ? It was moved out of line (so no need to hide a constant in a nop), deduped, and renamed to mds_verw_sel. verw _ASM_RIP(mds_verw_sel) *is* the memory form. ~Andrew