Re: [PATCH] kasan: test: fix compatibility with FORTIFY_SOURCE

[Kees Cook]

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@xxxxxxxxxx>
> Signed-off-by: Marco Elver <elver@xxxxxxxxxx>

Yup, more good fixes. Thanks!

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-- 
Kees Cook