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Thu, 09 Oct 2025 04:30:38 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFlP8l8EyfW7rcYqytt3jcelkFrNeuCHobP5tZUApaXWt6cy00Cg4gyA/v9+mAmCJ5tZDAP4g== X-Received: by 2002:a05:6000:1ac8:b0:3f7:b7ac:f3d4 with SMTP id ffacd0b85a97d-42666abbbc1mr5654561f8f.5.1760009437420; Thu, 09 Oct 2025 04:30:37 -0700 (PDT) Received: from [192.168.10.81] ([151.49.231.162]) by smtp.googlemail.com with ESMTPSA id ffacd0b85a97d-4255d8e9703sm34718441f8f.30.2025.10.09.04.30.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 09 Oct 2025 04:30:36 -0700 (PDT) Message-ID: <9e9f5f0b-ad40-44c2-97a3-9845f2e1ac6f@redhat.com> Date: Thu, 9 Oct 2025 13:30:35 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] target/i386: Add TSA feature flag verw-clear To: Babu Moger , zhao1.liu@intel.com, bp@alien8.de Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org References: <12881b2c03fa351316057ddc5f39c011074b4549.1752176771.git.babu.moger@amd.com> Content-Language: en-US From: Paolo Bonzini Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.438, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 7/10/25 21:46, Babu Moger wrote: > Transient Scheduler Attacks (TSA) are new speculative side channel attacks > related to the execution timing of instructions under specific > microarchitectural conditions. In some cases, an attacker may be able to > use this timing information to infer data from other contexts, resulting in > information leakage > > CPUID Fn8000_0021 EAX[5] (VERW_CLEAR). If this bit is 1, the memory form of > the VERW instruction may be used to help mitigate TSA. > > Link: https://www.amd.com/content/dam/amd/en/documents/resources/bulletin/technical-guidance-for-mitigating-transient-scheduler-attacks.pdf > Co-developed-by: Borislav Petkov (AMD) > Signed-off-by: Borislav Petkov (AMD) > Signed-off-by: Babu Moger Applied, thanks. Paolo > --- > v2: Split the patches into two. > Not adding the feature bit in CPU model now. Users can add the feature > bits by using the option "-cpu EPYC-Genoa,+verw-clear". > > v1: https://lore.kernel.org/qemu-devel/20250709104956.GAaG5JVO-74EF96hHO@fat_crate.local/ > --- > target/i386/cpu.c | 2 +- > target/i386/cpu.h | 2 ++ > 2 files changed, 3 insertions(+), 1 deletion(-) > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c > index 2cd07b86b5..d46bc65e44 100644 > --- a/target/i386/cpu.c > +++ b/target/i386/cpu.c > @@ -1274,7 +1274,7 @@ FeatureWordInfo feature_word_info[FEATURE_WORDS] = { > .type = CPUID_FEATURE_WORD, > .feat_names = { > "no-nested-data-bp", "fs-gs-base-ns", "lfence-always-serializing", NULL, > - NULL, NULL, "null-sel-clr-base", NULL, > + NULL, "verw-clear", "null-sel-clr-base", NULL, > "auto-ibrs", NULL, NULL, NULL, > NULL, NULL, NULL, NULL, > NULL, NULL, NULL, NULL, > diff --git a/target/i386/cpu.h b/target/i386/cpu.h > index 6a9eb2dbf7..4127acf1b1 100644 > --- a/target/i386/cpu.h > +++ b/target/i386/cpu.h > @@ -1102,6 +1102,8 @@ uint64_t x86_cpu_get_supported_feature_word(X86CPU *cpu, FeatureWord w); > #define CPUID_8000_0021_EAX_FS_GS_BASE_NS (1U << 1) > /* LFENCE is always serializing */ > #define CPUID_8000_0021_EAX_LFENCE_ALWAYS_SERIALIZING (1U << 2) > +/* Memory form of VERW mitigates TSA */ > +#define CPUID_8000_0021_EAX_VERW_CLEAR (1U << 5) > /* Null Selector Clears Base */ > #define CPUID_8000_0021_EAX_NULL_SEL_CLR_BASE (1U << 6) > /* Automatic IBRS */