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Mon, 19 Jan 2026 08:34:47 -0800 (PST) Message-ID: Date: Mon, 19 Jan 2026 17:33:35 +0100 Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 00/14] kasan: x86: arm64: KASAN tag-based mode for x86 To: Maciej Wieczor-Retman , corbet@lwn.net, morbo@google.com, rppt@kernel.org, lorenzo.stoakes@oracle.com, ubizjak@gmail.com, mingo@redhat.com, vincenzo.frascino@arm.com, maciej.wieczor-retman@intel.com, maz@kernel.org, catalin.marinas@arm.com, yeoreum.yun@arm.com, will@kernel.org, jackmanb@google.com, samuel.holland@sifive.com, glider@google.com, osandov@fb.com, nsc@kernel.org, luto@kernel.org, jpoimboe@kernel.org, akpm@linux-foundation.org, Liam.Howlett@oracle.com, kees@kernel.org, jan.kiszka@siemens.com, thomas.lendacky@amd.com, jeremy.linton@arm.com, dvyukov@google.com, axelrasmussen@google.com, leitao@debian.org, bigeasy@linutronix.de, peterz@infradead.org, mark.rutland@arm.com, urezki@gmail.com, brgerst@gmail.com, hpa@zytor.com, mhocko@suse.com, andreyknvl@gmail.com, weixugc@google.com, kbingham@kernel.org, vbabka@suse.cz, nathan@kernel.org, trintaeoitogc@gmail.com, samitolvanen@google.com, tglx@kernel.org, thuth@redhat.com, surenb@google.com, anshuman.khandual@arm.com, smostafa@google.com, yuanchu@google.com, ada.coupriediaz@arm.com, dave.hansen@linux.intel.com, kas@kernel.org, nick.desaulniers+lkml@gmail.com, david@kernel.org, bp@alien8.de, ardb@kernel.org, justinstitt@google.com Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com, llvm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, x86@kernel.org References: Content-Language: en-US From: Andrey Ryabinin In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 1/12/26 6:26 PM, Maciej Wieczor-Retman wrote: > ======= Compilation > Clang was used to compile the series (make LLVM=1) since gcc doesn't > seem to have support for KASAN tag-based compiler instrumentation on > x86. > It appears that GCC nominally supports this, but in practice it does not work. Here is a minimal reproducer: https://godbolt.org/z/s85e11T5r As far as I understand, calling a function through a tagged pointer is not supported by the hardware, so GCC attempts to clear the tag before the call. This behavior seems to be inherited from the userspace implementation of HWASan (-fsanitize=hwaddress). I have filed a GCC bug report: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123696 For the kernel, we probably do not want this masking at all, as effectively 99.9–100% of function pointer calls are expected to be untagged anyway. Clang does not appear to do this, not even for userspace.