linux-hardening - Re: [PATCH 6/9] fortify: Split reporting and avoid passing string pointer

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Date:   Thu, 6 Apr 2023 15:57:37 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     linux-hardening@...r.kernel.org, Andy Shevchenko <andy@...nel.org>,
        Cezary Rojewski <cezary.rojewski@...el.com>,
        Puyou Lu <puyou.lu@...il.com>, Mark Brown <broonie@...nel.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Brendan Higgins <brendan.higgins@...ux.dev>,
        David Gow <davidgow@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Miguel Ojeda <ojeda@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Liam Howlett <liam.howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Yury Norov <yury.norov@...il.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Sander Vanheule <sander@...nheule.net>,
        Eric Biggers <ebiggers@...gle.com>,
        "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Daniel Latypov <dlatypov@...gle.com>,
        José Expósito <jose.exposito89@...il.com>,
        linux-kernel@...r.kernel.org, kunit-dev@...glegroups.com
Subject: Re: [PATCH 6/9] fortify: Split reporting and avoid passing string
 pointer

On Thu, Apr 06, 2023 at 01:20:52PM +0300, Andy Shevchenko wrote:
> On Thu, Apr 6, 2023 at 3:02 AM Kees Cook <keescook@...omium.org> wrote:
> >
> > In preparation for KUnit testing and further improvements in fortify
> > failure reporting, split out the report and encode the function and
> > access failure (read or write overflow) into a single int argument. This
> > mainly ends up saving some space in the data segment. For a defconfig
> > with FORTIFY_SOURCE enabled:
> >
> > $ size gcc/vmlinux.before gcc/vmlinux.after
> >    text           data     bss     dec              hex filename
> > 26132309        9760658 2195460 38088427        2452eeb gcc/vmlinux.before
> > 26132386        9748382 2195460 38076228        244ff44 gcc/vmlinux.after
> 
> ...
> 
> > +       const char *name;
> > +       const bool write = !!(reason & 0x1);
> 
> Perhaps define that as
> 
> FORTIFY_READ_WRITE  BIT(0)
> FORTIFY_FUNC_SHIFT  1
> 
> const bool write = reason & FORTIFY_READ_WRITE; // and note no need for !! part

Yeah, that reads better. The FIELD_GET suggestion down-thread is
probably how I'll go.

> 
> switch (reason >> FORTIFY_FUNC_SHIFT) {
> 
> > +       switch (reason >> 1) {
> > +       case FORTIFY_FUNC_strncpy:
> > +               name = "strncpy";
> > +               break;
> > +       case FORTIFY_FUNC_strnlen:
> > +               name = "strnlen";
> > +               break;
> > +       case FORTIFY_FUNC_strlen:
> > +               name = "strlen";
> > +               break;
> > +       case FORTIFY_FUNC_strlcpy:
> > +               name = "strlcpy";
> > +               break;
> > +       case FORTIFY_FUNC_strscpy:
> > +               name = "strscpy";
> > +               break;
> > +       case FORTIFY_FUNC_strlcat:
> > +               name = "strlcat";
> > +               break;
> > +       case FORTIFY_FUNC_strcat:
> > +               name = "strcat";
> > +               break;
> > +       case FORTIFY_FUNC_strncat:
> > +               name = "strncat";
> > +               break;
> > +       case FORTIFY_FUNC_memset:
> > +               name = "memset";
> > +               break;
> > +       case FORTIFY_FUNC_memcpy:
> > +               name = "memcpy";
> > +               break;
> > +       case FORTIFY_FUNC_memmove:
> > +               name = "memmove";
> > +               break;
> > +       case FORTIFY_FUNC_memscan:
> > +               name = "memscan";
> > +               break;
> > +       case FORTIFY_FUNC_memcmp:
> > +               name = "memcmp";
> > +               break;
> > +       case FORTIFY_FUNC_memchr:
> > +               name = "memchr";
> > +               break;
> > +       case FORTIFY_FUNC_memchr_inv:
> > +               name = "memchr_inv";
> > +               break;
> > +       case FORTIFY_FUNC_kmemdup:
> > +               name = "kmemdup";
> > +               break;
> > +       case FORTIFY_FUNC_strcpy:
> > +               name = "strcpy";
> > +               break;
> > +       default:
> > +               name = "unknown";
> > +       }
> 
> ...
> 
> > +       WARN(1, "%s: detected buffer %s overflow\n", name, write ? "write" : "read");
> 
> Using str_read_write() ?
> 
> Dunno if it's already there or needs to be added. I have some patches
> to move those str_*() to string_choices.h. We can also prepend yours
> with those.

Oh! Hah. I totally forgot about str_read_write. :) I will use that.

-- 
Kees Cook