linux-hardening - Re: [PATCH] kasan: test: fix compatibility with FORTIFY

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Date:   Mon, 24 Jan 2022 10:24:34 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Marco Elver <elver@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Brendan Higgins <brendanhiggins@...gle.com>,
        linux-hardening@...r.kernel.org, Nico Pache <npache@...hat.com>
Subject: Re: [PATCH] kasan: test: fix compatibility with FORTIFY_SOURCE

On Mon, Jan 24, 2022 at 05:07:44PM +0100, Marco Elver wrote:
> With CONFIG_FORTIFY_SOURCE enabled, string functions will also perform
> dynamic checks using __builtin_object_size(ptr), which when failed will
> panic the kernel.
> 
> Because the KASAN test deliberately performs out-of-bounds operations,
> the kernel panics with FORITY_SOURCE, for example:
> 
>  | kernel BUG at lib/string_helpers.c:910!
>  | invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
>  | CPU: 1 PID: 137 Comm: kunit_try_catch Tainted: G    B             5.16.0-rc3+ #3
>  | Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
>  | RIP: 0010:fortify_panic+0x19/0x1b
>  | ...
>  | Call Trace:
>  |  <TASK>
>  |  kmalloc_oob_in_memset.cold+0x16/0x16
>  |  ...
> 
> Fix it by also hiding `ptr` from the optimizer, which will ensure that
> __builtin_object_size() does not return a valid size, preventing
> fortified string functions from panicking.
> 
> Reported-by: Nico Pache <npache@...hat.com>
> Signed-off-by: Marco Elver <elver@...gle.com>

Yup, more good fixes. Thanks!

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook