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[92.26.98.202]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-454a999d399sm10529085e9.25.2025.07.02.16.42.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 02 Jul 2025 16:42:29 -0700 (PDT) Message-ID: <4dcd23cb-eb55-42e7-aa76-dbaf2e2a7e07@citrix.com> Date: Thu, 3 Jul 2025 00:42:27 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: hpa@zytor.com Cc: acme@redhat.com, aik@amd.com, akpm@linux-foundation.org, alexander.shishkin@linux.intel.com, ardb@kernel.org, ast@kernel.org, bp@alien8.de, brijesh.singh@amd.com, changbin.du@huawei.com, christophe.leroy@csgroup.eu, corbet@lwn.net, daniel.sneddon@linux.intel.com, dave.hansen@linux.intel.com, ebiggers@google.com, geert+renesas@glider.be, houtao1@huawei.com, jgg@ziepe.ca, jgross@suse.com, jpoimboe@kernel.org, kai.huang@intel.com, kees@kernel.org, kirill.shutemov@linux.intel.com, leitao@debian.org, linux-doc@vger.kernel.org, linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux@rasmusvillemoes.dk, luto@kernel.org, mcgrof@kernel.org, mhiramat@kernel.org, michael.roth@amd.com, mingo@kernel.org, mingo@redhat.com, namhyung@kernel.org, paulmck@kernel.org, pawan.kumar.gupta@linux.intel.com, peterz@infradead.org, rick.p.edgecombe@intel.com, rppt@kernel.org, sandipan.das@amd.com, shijie@os.amperecomputing.com, sohil.mehta@intel.com, tglx@linutronix.de, tj@kernel.org, tony.luck@intel.com, vegard.nossum@oracle.com, x86@kernel.org, xin3.li@intel.com, xiongwei.song@windriver.com, ytcoode@gmail.com References: <4DE45AFD-C1E0-4FB8-BE01-44A72C5C6E1E@zytor.com> Subject: Re: [PATCHv8 14/17] x86/traps: Handle LASS thrown #SS Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 960A8120007 X-Stat-Signature: 49exuhkgad77wwccyrr7artqbsxhejr3 X-Rspam-User: X-HE-Tag: 1751499751-595261 X-HE-Meta: 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 Svw7WXxD 7aAaPHblDtFRdj3BdZoLgWmHBBRnTQLmh94WovKTUlx9eQW6BfhokSYvN0uh0a95+UDDqLrI4Hj3Q9mrsmzHKKdOmUTaTK17Yr9UTguNqiLKkezMZ2FyL/pzw98jSLHtPL190dl4hkYCnv+Lx/a32D1yPQDqTAcbGheLUBcN2dKUz5p/umBg/8roKk0AqmrTMkOH7+P92zdRnYJTIjMmJV2CxttjE7+tGw/AVdJnI1NUWdFNj8HfXbwXWDqZvCM96p/EBfqQetai2ATS06uBWeqNUJmZkO/qKSWNbvDm+w2TOjocQo6B/CRe2s4kgMfw2Rpiqpj9NDCUc4Res4ViIfW0B/GP9rnlSLFbJj59E01AbmFOW35dZGKaEYM2o8zt0Mwk23gL/VRrP0pibxZ4UXIJ9KK67G0tbW7RTYLZ+p+PMLHOIgcOqgf9i9vCcvVLW1jBMkvnWGdVe8m9iqb+wFNU+yfrHhcyCfuqzM1ov1ozvaHd/zrfHaE4BE57/pKaDQHp0YkTSnQyJ0DwGOMhj/G7r78q+fs/bqO6qG123VYnTfdZLlknv8ViYqOqoK8b415MfTGMCWEH3SrcntK0nUvSlJjkdzaL5KXlhoT32Ui1UPvs= 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: List-Subscribe: List-Unsubscribe: > Note: for a FRED system, ERETU can generate #SS for a non-canonical user space RSP How?  Or to phrase it differently, I hope not. %rsp is a 64bit value and does not have canonical restrictions elsewhere in the architecture, so far as I'm aware.  IRET really can restore a non-canonical %rsp, and userspace can run for an indeterminate period of time with a non-canonical %rsp as long as there are no stack accesses. Accesses relative to the the stack using a non-canonical pointer will suffer #SS, but ERETU doesn't modify the userspace stack AFAICT.  I can't see anything in the ERETU pseudocode in the FRED spec that mentions a canonical check or memory access using %rsp. ~Andrew