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X-CSE-ConnectionGUID: FOCoGt6BTnewDSG3rh80bw== X-CSE-MsgGUID: WA4HGncaTZuAboHpsCdtIQ== X-IronPort-AV: E=McAfee;i="6700,10204,11394"; a="49022881" X-IronPort-AV: E=Sophos;i="6.15,188,1739865600"; d="scan'208";a="49022881" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by orvoesa106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Apr 2025 09:06:57 -0700 X-CSE-ConnectionGUID: cO+Z9NzfR/u/1zgGGwdspw== X-CSE-MsgGUID: 96Ikxg4US7+bKvi55n+CVw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.15,188,1739865600"; d="scan'208";a="164554384" Received: from daliomra-mobl3.amr.corp.intel.com (HELO [10.124.223.29]) ([10.124.223.29]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Apr 2025 09:06:54 -0700 Message-ID: <3fd46452-fc96-4d50-9c40-a8a453d58f40@intel.com> Date: Fri, 4 Apr 2025 09:06:51 -0700 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 03/14] x86: Add arch specific kasan functions To: Maciej Wieczor-Retman , hpa@zytor.com, hch@infradead.org, nick.desaulniers+lkml@gmail.com, kuan-ying.lee@canonical.com, masahiroy@kernel.org, samuel.holland@sifive.com, mingo@redhat.com, corbet@lwn.net, ryabinin.a.a@gmail.com, guoweikang.kernel@gmail.com, jpoimboe@kernel.org, ardb@kernel.org, vincenzo.frascino@arm.com, glider@google.com, kirill.shutemov@linux.intel.com, apopple@nvidia.com, samitolvanen@google.com, kaleshsingh@google.com, jgross@suse.com, andreyknvl@gmail.com, scott@os.amperecomputing.com, tony.luck@intel.com, dvyukov@google.com, pasha.tatashin@soleen.com, ziy@nvidia.com, broonie@kernel.org, gatlin.newhouse@gmail.com, jackmanb@google.com, wangkefeng.wang@huawei.com, thiago.bauermann@linaro.org, tglx@linutronix.de, kees@kernel.org, akpm@linux-foundation.org, jason.andryuk@amd.com, snovitoll@gmail.com, xin@zytor.com, jan.kiszka@siemens.com, bp@alien8.de, rppt@kernel.org, peterz@infradead.org, pankaj.gupta@amd.com, thuth@redhat.com, andriy.shevchenko@linux.intel.com, joel.granados@kernel.org, kbingham@kernel.org, nicolas@fjasle.eu, mark.rutland@arm.com, surenb@google.com, catalin.marinas@arm.com, morbo@google.com, justinstitt@google.com, ubizjak@gmail.com, jhubbard@nvidia.com, urezki@gmail.com, dave.hansen@linux.intel.com, bhe@redhat.com, luto@kernel.org, baohua@kernel.org, nathan@kernel.org, will@kernel.org, brgerst@gmail.com Cc: llvm@lists.linux.dev, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, x86@kernel.org References: From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/4/25 06:14, Maciej Wieczor-Retman wrote: > +static inline const void *__tag_set(const void *addr, u8 tag) > +{ > + u64 __addr = (u64)addr & ~__tag_shifted(KASAN_TAG_KERNEL); > + return (const void *)(__addr | __tag_shifted(tag)); > +} This becomes a lot clearer to read if you separate out the casting from the logical bit manipulation. For instance: static inline const void *__tag_set(const void *__addr, u8 tag) { u64 addr = (u64)__addr; addr &= ~__tag_shifted(KASAN_TAG_KERNEL); addr |= __tag_shifted(tag); return (const void *)addr; } Also, unless there's a good reason for it, you might as well limit the places you need to use "__". Now that we can read this, I think it's potentially buggy. If someone went and changed: #define KASAN_TAG_KERNEL 0xFF to, say: #define KASAN_TAG_KERNEL 0xAB the '&' would miss clearing bits. It works fine in the arm64 implementation: u64 __addr = (u64)addr & ~__tag_shifted(0xff); because they've hard-coded 0xff. I _think_ that's what you actually want here. You don't want to mask out KASAN_TAG_KERNEL, you actually want to mask out *ANYTHING* in those bits. So the best thing is probably to define a KASAN_TAG_MASK that makes it clear which are the tag bits.