Re: [PATCH] fortify: Use WARN instead of BUG for now

Kees Cook
2017-07-26T17:17:28Z

On Wed, Jul 26, 2017 at 10:10 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Tue, Jul 25, 2017 at 8:50 PM, Kees Cook <keescook@chromium.org> wrote:
>> +
>> +void fortify_read_overflow(const char *func)
>> {
>> - pr_emerg("detected buffer overflow in %s\n", name);
>> - BUG();
>> + WARN(1, "detected read beyond size of object passed as 1st parameter in %s\n", func);
>> }
>
> Side note: have you actually checked the code generation of this all?
>
> In particular, do you have any reason to use the out-of-line
> functions? Our WARN() code isn't horrible, and isn't likely to be
> noticeably worse than your own explicit out-of-lining. And you'd get
> the "unlikely()" for free, so you'll possibly get smaller code that
> runs better too.
>
> And it would even *look* better. This:
>
> if (p_size < size)
> fortify_read_overflow(__func__);
>
> would become
>
> WARN(p_size < size, "kmemdup size overflow");
>
> or something.

I did, yeah. It's actually slightly smaller code size to out-of-line these:

$ size vmlinux.fortify*
text data bss dec hex filename
10903767 5605009 13930496 30439272 1d07768
vmlinux.fortify-off
10944795 5617801 13930496 30493092 1d149a4 vmlinux.fortify
10950117 5626725 13930496 30507338 1d1814a
vmlinux.fortify-inline

If the readability improvement is preferred over the growth in size, I
can certainly respin it.

-Kees

--
Kees Cook
Pixel Security