linux-kernel - Re: [PATCH 4/4] fortify: Use __builtin_dynamic_object

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Message-ID: <0da67f73-dd73-7e6d-74c2-14aec5d79902@gotplt.org>
Date:   Tue, 22 Nov 2022 05:20:37 -0500
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.
> 
> Additionally update the VMALLOC_LINEAR_OVERFLOW LKDTM test to make the
> hint invisible, otherwise the architectural defense is not exercised
> (the buffer overflow is detected in the memset() rather than when it
> crosses the edge of the allocation).
> 
> Cc: Miguel Ojeda <ojeda@...nel.org>
> Cc: Siddhesh Poyarekar <siddhesh@...plt.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Nathan Chancellor <nathan@...nel.org>
> Cc: Tom Rix <trix@...hat.com>
> Cc: linux-hardening@...r.kernel.org
> Cc: llvm@...ts.linux.dev
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>   drivers/misc/lkdtm/heap.c           | 1 +
>   include/linux/compiler_attributes.h | 5 +++++
>   include/linux/fortify-string.h      | 7 +++++++
>   3 files changed, 13 insertions(+)

Hi Kees,

Circling back on this, I noticed that all but this patch got pulled into 
Linus' tree.  Is there a reason why this has been held back?

Thanks,
Sid