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Wed, 21 Sep 2022 04:43:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gotplt.org; s=dreamhost; t=1663760606; bh=47nEMkjYsLXQ6Ot/FDVaWGYLcBDevAZpyjCyYbZxiw0=; h=Date:Subject:To:Cc:From:Content-Type:Content-Transfer-Encoding; b=CZUfUAJpWTYlImU2ZXuYcyQK007mxDfXXMFolecWpXffOmrOZKKZ68zbRiCD7X1n4 eMyOtl29ST3OvtwAAr/ksKnX41fYQH5Of8gFdZ3MaXE/8jJNlDrCIHDAL42G4hxInw CAQC5eRQiqDtCl04fn/58I371UlzKf4CbqiiDCn3h+gvGaaIWNixw5PVqIu1peXNyu NtVn0C4qu8V8MLqPrBoDfS09USVcUDWmFjVjQmnWjQLQ6t5XcZulp3r55O7Nc7Bg0P US5UMMdWoGtAYEOOzPzUN4N+2mjRMtdcJ6SvWv9TLBVqSLwltCiVX4FJWE/qbEvEsf ud2nnmJ+kCejQ== Message-ID: <9d80e0a3-3fcc-0676-4529-79743f418557@gotplt.org> Date: Wed, 21 Sep 2022 07:43:17 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [PATCH 4/4] fortify: Use __builtin_dynamic_object_size() when available Content-Language: en-US To: Kees Cook , linux-hardening@vger.kernel.org Cc: Miguel Ojeda , Arnd Bergmann , Nick Desaulniers , Nathan Chancellor , Tom Rix , llvm@lists.linux.dev, Juergen Gross , Boris Ostrovsky , linux-kernel@vger.kernel.org References: <20220920192202.190793-1-keescook@chromium.org> <20220920192202.190793-5-keescook@chromium.org> From: Siddhesh Poyarekar In-Reply-To: <20220920192202.190793-5-keescook@chromium.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org On 2022-09-20 15:22, Kees Cook wrote: > Since the commits starting with c37495d6254c ("slab: add __alloc_size > attributes for better bounds checking"), the compilers have runtime > allocation size hints available in some places. This was immediately > available to CONFIG_UBSAN_BOUNDS, but CONFIG_FORTIFY_SOURCE needed > updating to explicitly make use the hints via the associated > __builtin_dynamic_object_size() helper. Detect and use the builtin when > it is available, increasing the accuracy of the mitigation. When runtime > sizes are not available, __builtin_dynamic_object_size() falls back to > __builtin_object_size(), leaving the existing bounds checking unchanged. I don't know yet what the overhead is for __builtin_dynamic_object_size vs __builtin_object_size, were you able to measure it somehow for the kernel? If there's a significant tradeoff, it may make sense to provide a user override. Thanks, Sid