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a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1781844397; bh=zo7L85WEMQspgr+Xxc8ITBFT//tY1Z8VCvuSv/cXyLE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=UFR0HsfmIgbVnXQm+nqkHxhtgz5uJsi6PxQu6nA5ExDABz7YYRT7NN2ntqyfACtfc YYTLIoQYxo0u00Td35Ce4bhkgZmFJh0u8l1EU5h2mEcWWIy16lRJl/KwhmY7mFTxOW hsefNn6008dILDD8tAKp+MmYZbEaeZK3tVneAAno= Message-ID: <9abb0da8-e29a-46ce-af11-55c49b30b1b2@arm.com> Date: Fri, 19 Jun 2026 10:16:27 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/2] kasan: hw_tags: Add option to tag only at allocation time To: Lance Yang Cc: ryabinin.a.a@gmail.com, akpm@linux-foundation.org, corbet@lwn.net, glider@google.com, andreyknvl@gmail.com, dvyukov@google.com, vincenzo.frascino@arm.com, kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, workflows@vger.kernel.org, linux-doc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, kaleshsingh@google.com, 21cnbao@gmail.com, david@kernel.org, will@kernel.org, catalin.marinas@arm.com References: <20260612044425.763060-1-dev.jain@arm.com> <20260613060637.40039-1-lance.yang@linux.dev> Content-Language: en-US From: Dev Jain In-Reply-To: <20260613060637.40039-1-lance.yang@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 3ex1sdotanjw5xc8g881ihomhijibzy8 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: F134FA0006 X-Rspam-User: X-HE-Tag: 1781844397-862162 X-HE-Meta: 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 jToL9YEa TE8559iS9GpUd846iuEGvGulT7kk7AQBBt60cOIYlOZyMqrHryHEQ2M8jLEgP81aczXpqvnb3hx8aDMKnqJvcqaykl787WgptWRhJ/u5EO5BZVbaV7imxartg5/KSL+9ePqmZTU4iG6Dao7Pn888wZc9GIPDS2mJ2y9RPJyYbwY3x9Px6il3Gh3RMKtw9R6i6bpAwzkymIhZGOFaF6dCas+rtyQVub+0vL6w+2EK+L1Wwp6owz5uVFguUFI7T0lw/ZNFCSHvZIFrVyOJpx7JClVs4Ln6U81Kc9M1GCVhvHOnSBhX6BLOFrPTdUbM/RBesu4NgthUyCW2C4P8wAxyNYFY3J7gcJln5K/DOLmm5g9tzuvk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 13/06/26 11:36 am, Lance Yang wrote: > > On Fri, Jun 12, 2026 at 04:44:22AM +0000, Dev Jain wrote: >> Introduce a boot option to tag only at allocation time of the objects. This >> reduces KASAN MTE overhead, the tradeoff being reduced ability of >> catching bugs. >> >> Now, when a memory object will be freed, it will retain the random tag it >> had at allocation time. This compromises on catching UAF bugs, till the >> time the object is not reallocated, at which point it will have a new >> random tag. >> >> Hence, not catching "use-after-free-before-reallocation" and not catching >> "double-free" will be the compromise for reduced KASAN overhead. > > Hmm ... do we also need to teach the KASAN KUnit tests about this mode? > > With kasan.tag_only_on_alloc=on, free-time poisoning is skipped, so > some UAF and double-free reports are skipped on purpose, but the tests > still expect them :) Yeah my opinion is that we shouldn't bother - but if we go ahead with this patch in some shape or form then I'll see how to make kasan_test work with this. > > Cheers, Lance >