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Message-ID: <9d80e0a3-3fcc-0676-4529-79743f418557@gotplt.org> Date: Wed, 21 Sep 2022 07:43:17 -0400 From: Siddhesh Poyarekar <siddhesh@...plt.org> To: Kees Cook <keescook@...omium.org>, linux-hardening@...r.kernel.org Cc: Miguel Ojeda <ojeda@...nel.org>, Arnd Bergmann <arnd@...db.de>, Nick Desaulniers <ndesaulniers@...gle.com>, Nathan Chancellor <nathan@...nel.org>, Tom Rix <trix@...hat.com>, llvm@...ts.linux.dev, Juergen Gross <jgross@...e.com>, Boris Ostrovsky <boris.ostrovsky@...cle.com>, linux-kernel@...r.kernel.org Subject: Re: [PATCH 4/4] fortify: Use __builtin_dynamic_object_size() when available 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
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