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From: Kees Cook <keescook@chromium.org>
To: Siddhesh Poyarekar <siddhesh@gotplt.org>
Cc: linux-hardening@vger.kernel.org, Miguel Ojeda <ojeda@kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nathan Chancellor <nathan@kernel.org>, Tom Rix <trix@redhat.com>,
	llvm@lists.linux.dev, Juergen Gross <jgross@suse.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/4] fortify: Use __builtin_dynamic_object_size() when available
Date: Wed, 21 Sep 2022 20:33:52 -0700	[thread overview]
Message-ID: <202209212032.5F392F42@keescook> (raw)
In-Reply-To: <9d80e0a3-3fcc-0676-4529-79743f418557@gotplt.org>

On Wed, Sep 21, 2022 at 07:43:17AM -0400, Siddhesh Poyarekar wrote:
> 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.

So far I've not seen any measurable performance difference, but I just
may not be creative enough yet.

So far, the tunable is building a kernel with or without FORTIFY_SOURCE
and UBSAN_BOUNDS. :)

-- 
Kees Cook

  reply	other threads:[~2022-09-22  3:33 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-20 19:21 [PATCH 0/4] fortify: Use __builtin_dynamic_object_size() when available Kees Cook
2022-09-20 19:21 ` [PATCH 1/4] x86/entry: Work around Clang __bdos() bug Kees Cook
2022-09-21  0:07   ` Boris Ostrovsky
2022-09-20 19:22 ` [PATCH 2/4] fortify: Explicitly check bounds are compile-time constants Kees Cook
2022-09-21 11:48   ` Siddhesh Poyarekar
2022-09-22  3:46     ` Kees Cook
2022-09-20 19:22 ` [PATCH 3/4] fortify: Convert to struct vs member helpers Kees Cook
2022-09-20 19:22 ` [PATCH 4/4] fortify: Use __builtin_dynamic_object_size() when available Kees Cook
2022-09-21 11:24   ` Miguel Ojeda
2022-09-21 11:43   ` Siddhesh Poyarekar
2022-09-22  3:33     ` Kees Cook [this message]
2022-09-22 14:45       ` Siddhesh Poyarekar
2022-11-22 10:20   ` Siddhesh Poyarekar
2022-11-23  5:15     ` Kees Cook
2022-11-23 15:29       ` Siddhesh Poyarekar
2023-01-13 15:59   ` linux-next - bxnt buffer overflow in strnlen Niklas Cassel
2023-01-13 16:08     ` linux-next - bnxt " Niklas Cassel
2023-01-13 22:44       ` Kees Cook
2023-01-16 10:56         ` Niklas Cassel
2022-09-22 20:26 ` [PATCH 0/4] fortify: Use __builtin_dynamic_object_size() when available Siddhesh Poyarekar
2022-09-23  0:20   ` Kees Cook
2022-09-23  0:55     ` Siddhesh Poyarekar

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