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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id c10-20020a63724a000000b0055386b1415dsm1802755pgn.51.2023.07.11.09.14.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Jul 2023 09:14:49 -0700 (PDT) Date: Tue, 11 Jul 2023 09:14:49 -0700 From: Kees Cook To: Vlastimil Babka Cc: Christoph Lameter , David Rientjes , Pekka Enberg , Joonsoo Kim , Hyeonggon Yoo <42.hyeyoo@gmail.com>, Roman Gushchin , linux-mm@kvack.org, patches@lists.linux.dev, linux-kernel@vger.kernel.org, Matteo Rizzo , Jann Horn , Andrey Konovalov , Marco Elver , Alexander Potapenko , kasan-dev@googlegroups.com, linux-hardening@vger.kernel.org Subject: Re: [PATCH 1/2] mm/slub: remove redundant kasan_reset_tag() from freelist_ptr calculations Message-ID: <202307110914.8D460C7@keescook> References: <20230711134623.12695-3-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230711134623.12695-3-vbabka@suse.cz> X-Rspamd-Queue-Id: 9F40FC0007 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: yxgkd3jzpu9oqp4yifh5sxxrkykwz5z3 X-HE-Tag: 1689092091-735633 X-HE-Meta: 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 yGevY/1T 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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: On Tue, Jul 11, 2023 at 03:46:24PM +0200, Vlastimil Babka wrote: > Commit d36a63a943e3 ("kasan, slub: fix more conflicts with > CONFIG_SLAB_FREELIST_HARDENED") has introduced kasan_reset_tags() to > freelist_ptr() encoding/decoding when CONFIG_SLAB_FREELIST_HARDENED is > enabled to resolve issues when passing tagged or untagged pointers > inconsistently would lead to incorrect calculations. > > Later, commit aa1ef4d7b3f6 ("kasan, mm: reset tags when accessing > metadata") made sure all pointers have tags reset regardless of > CONFIG_SLAB_FREELIST_HARDENED, because there was no other way to access > the freepointer metadata safely with hw tag-based KASAN. > > Therefore the kasan_reset_tag() usage in freelist_ptr_encode()/decode() > is now redundant, as all callers use kasan_reset_tag() unconditionally > when constructing ptr_addr. Remove the redundant calls and simplify the > code and remove obsolete comments. > > Also in freelist_ptr_encode() introduce an 'encoded' variable to make > the lines shorter and make it similar to the _decode() one. > > Signed-off-by: Vlastimil Babka Thanks, this is much more readable! Acked-by: Kees Cook -- Kees Cook