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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4587ac58045sm110653695e9.22.2025.07.28.12.11.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Jul 2025 12:11:39 -0700 (PDT) Date: Mon, 28 Jul 2025 20:11:37 +0100 From: David Laight To: "Kirill A. Shutemov" Cc: Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Peter Zijlstra , Ard Biesheuvel , "Paul E. McKenney" , Josh Poimboeuf , Xiongwei Song , Xin Li , "Mike Rapoport (IBM)" , Brijesh Singh , Michael Roth , Tony Luck , Alexey Kardashevskiy , Alexander Shishkin , Jonathan Corbet , Sohil Mehta , Ingo Molnar , Pawan Gupta , Daniel Sneddon , Kai Huang , Sandipan Das , Breno Leitao , Rick Edgecombe , Alexei Starovoitov , Hou Tao , Juergen Gross , Vegard Nossum , Kees Cook , Eric Biggers , Jason Gunthorpe , "Masami Hiramatsu (Google)" , Andrew Morton , Luis Chamberlain , Yuntao Wang , Rasmus Villemoes , Christophe Leroy , Tejun Heo , Changbin Du , Huang Shijie , Geert Uytterhoeven , Namhyung Kim , Arnaldo Carvalho de Melo , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCHv9 02/16] x86/alternatives: Disable LASS when patching kernel alternatives Message-ID: <20250728201137.113d0f45@pumpkin> In-Reply-To: <20250707080317.3791624-3-kirill.shutemov@linux.intel.com> References: <20250707080317.3791624-1-kirill.shutemov@linux.intel.com> <20250707080317.3791624-3-kirill.shutemov@linux.intel.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: 15penmziigknbdj8kr5g3txbw993h7xi X-Rspamd-Queue-Id: 807E41A0007 X-Rspamd-Server: rspam10 X-Rspam-User: X-HE-Tag: 1753729901-683430 X-HE-Meta: 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 TuD1qbgu 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 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 Mon, 7 Jul 2025 11:03:02 +0300 "Kirill A. Shutemov" wrote: > From: Sohil Mehta > > For patching, the kernel initializes a temporary mm area in the lower > half of the address range. See commit 4fc19708b165 ("x86/alternatives: > Initialize temporary mm for patching"). > > Disable LASS enforcement during patching to avoid triggering a #GP > fault. > > The objtool warns due to a call to a non-allowed function that exists > outside of the stac/clac guard, or references to any function with a > dynamic function pointer inside the guard. See the Objtool warnings > section #9 in the document tools/objtool/Documentation/objtool.txt. > > Considering that patching is usually small, replace the memcpy() and > memset() functions in the text poking functions with their open coded > versions. ... Or just write a byte copy loop in C with (eg) barrier() inside it to stop gcc converting it to memcpy(). David