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Peter Anvin" To: Andrew Cooper 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 Subject: Re: [PATCHv8 14/17] x86/traps: Handle LASS thrown #SS User-Agent: K-9 Mail for Android In-Reply-To: <4dcd23cb-eb55-42e7-aa76-dbaf2e2a7e07@citrix.com> References: <4DE45AFD-C1E0-4FB8-BE01-44A72C5C6E1E@zytor.com> <4dcd23cb-eb55-42e7-aa76-dbaf2e2a7e07@citrix.com> Message-ID: <5F0DC7C6-58D9-4316-AFCB-3F002601DA9F@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 918DA14000C X-Stat-Signature: ngk1meymzy9iw3dhf5fbr9f19h4s5rnn X-Rspam-User: X-HE-Tag: 1751503537-324398 X-HE-Meta: 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 2ynq3IeI zS17XsxYYMpppFZ6NAnRAnrEhyMXdiyRSzVjkZVBdnCvbw8QUNLOX2weXprdurEzK+oYYWkZRYxjid8vZoASMHpcxF/h7VC6EhQ47hKnhYy1ea0zc/3TMX0crMJ/A7PXj/fLsKD7a5IiFk9SD3jTEPxz7RwGkKA69D2NCNPwoEwr9wehUfHeKMNzRhrmaDDp+KkdJGE36xufaM1BhGaj5ZBGtV+dLi6PO4V04kdWfSpSAP5Ca6AzV/BsKUwlBZzkyXh0ZOsOCYWlUoYknhrD71xP5i6LM2VlMt4vd1PByx2xaNdgUPWE9XyowqVPrnh2WKnWuXQotaNRQbtRGqUOm37qSzRcsstqOGTgLUBR9f8jsljUvpaWEQR5TFV9o6OizBBN6Xe6gZvxVHoYh5w5f/6IpFN08IeD4ULMB 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: On July 2, 2025 4:42:27 PM PDT, Andrew Cooper wrote: >> Note: for a FRED system, ERETU can generate #SS for a non-canonical use= r space RSP > >How?=C2=A0 Or to phrase it differently, I hope not=2E > >%rsp is a 64bit value and does not have canonical restrictions elsewhere >in the architecture, so far as I'm aware=2E=C2=A0 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=2E > >Accesses relative to the the stack using a non-canonical pointer will >suffer #SS, but ERETU doesn't modify the userspace stack AFAICT=2E=C2=A0 = I >can't see anything in the ERETU pseudocode in the FRED spec that >mentions a canonical check or memory access using %rsp=2E > >~Andrew You are right of course=2E Brainfart on my part=2E