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Date:   Wed, 21 Sep 2022 07:43:17 -0400
From:   Siddhesh Poyarekar <>
To:     Kees Cook <>,
Cc:     Miguel Ojeda <>, Arnd Bergmann <>,
        Nick Desaulniers <>,
        Nathan Chancellor <>,
        Tom Rix <>,,
        Juergen Gross <>,
        Boris Ostrovsky <>,
Subject: Re: [PATCH 4/4] fortify: Use __builtin_dynamic_object_size() when

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
> 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.


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