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s=dkim; t=1670497810; h=from:from: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:in-reply-to:in-reply-to: references:references; bh=Y/dlSQlwaW6qqeNkhgJdMiH59ouL4apa5gZVhWMRT4s=; b=OIZbB3qKghdj4LPSM4aWEbdKWePHGUg9m/dkgnuGHHorlGvJt/6A/5MtjRDEkp/BYrnBwK dhLIwBIRMimV1yafWmfJkl9EYOniXpgobWwReEQMDC2Zc7YirkrfR2w1WA/PGqhrg8VcMP BCBqUTPb9r3BSNwJ+is8NjGnKjKjctw= Date: Thu, 8 Dec 2022 12:10:10 +0100 From: Borislav Petkov To: "Edgecombe, Rick P" Cc: "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "peterz@infradead.org" , "rdunlap@infradead.org" , "keescook@chromium.org" , "Yu, Yu-cheng" , "dave.hansen@linux.intel.com" , "kirill.shutemov@linux.intel.com" , "Eranian, Stephane" , "linux-mm@kvack.org" , "fweimer@redhat.com" , "nadav.amit@gmail.com" , "jannh@google.com" , "dethoma@microsoft.com" , "kcc@google.com" , "linux-arch@vger.kernel.org" , "pavel@ucw.cz" , "oleg@redhat.com" , "hjl.tools@gmail.com" , "Yang, Weijiang" , "Lutomirski, Andy" , "linux-doc@vger.kernel.org" , "arnd@arndb.de" , "tglx@linutronix.de" , "Schimpe, Christina" , "mike.kravetz@oracle.com" , "x86@kernel.org" , "akpm@linux-foundation.org" , "jamorris@linux.microsoft.com" , "john.allen@amd.com" , "rppt@kernel.org" , "andrew.cooper3@citrix.com" , "mingo@redhat.com" , "corbet@lwn.net" , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , "gorcunov@gmail.com" Subject: Re: [PATCH v4 03/39] x86/cpufeatures: Add CPU feature flags for shadow stacks Message-ID: References: <20221203003606.6838-1-rick.p.edgecombe@intel.com> <20221203003606.6838-4-rick.p.edgecombe@intel.com> <63ea77f5d14739f8184ea51a4df939a58b4764ab.camel@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <63ea77f5d14739f8184ea51a4df939a58b4764ab.camel@intel.com> X-Rspamd-Queue-Id: CD338140009 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: e4kf9sq9dgneoht6jk8rkusub9wadnto X-HE-Tag: 1670497813-297980 X-HE-Meta: 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 7tOpQ757 QdBvSrjG5/SXM5/XE+0HnaX8+r+yZTqvtGUJdlywgieTyxM7Bx1nOMZ7RKygg37BlikdPiQd550uQA6m0y0TBWXoOGM/4GgTUTABCMdcGWb7XRkTbSzKZr1g0YdooACoKISlV X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Dec 07, 2022 at 10:35:59PM +0000, Edgecombe, Rick P wrote: > Yes, the suggestion was to have one for kernel and one for user. But I > was also thinking about how KVM could hypothetically support shadow > stack in guests in the non !CONFIG_X86_USER_SHADOW_STACK case (it only > needs CET_U xsave support). So that configuration wouldn't expose > user_shstk and since KVM's guest feature support is retrieved > programmatically, it could be nice to have some hint for KVM users that > they could try. Maybe it's simpler to just tie KVM and host support > together though. I'll remove "shstk". Hmm, I don't have a clear idea how guest shstk support should do so maybe this is all way off but yeah, if the host supports CET - the *hardware* feature - then you can use the same logic to support that in a VM. I.e., if the guest sees CET - i.e., HV has advertized it - then guest kernel behaves exactly the same as on the host. But it is likely I'm missing something more involved... Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette