linux-hardening - Re: [PATCH v2 07/10] fortify: Split reporting and avoid passing string pointer

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Date:   Thu, 20 Apr 2023 17:52:40 +0200
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     Kees Cook <keescook@...omium.org>
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 v2 07/10] fortify: Split reporting and avoid passing
 string pointer

From: Kees Cook <keescook@...omium.org>
Date: Fri,  7 Apr 2023 12:27:13 -0700

> 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 u8 argument. This
> mainly ends up saving some space in the data segment. For a defconfig
> with FORTIFY_SOURCE enabled:

[...]

> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
> index 230020a2e076..96d502e1e578 100644
> --- a/lib/string_helpers.c
> +++ b/lib/string_helpers.c
> @@ -1021,10 +1021,27 @@ EXPORT_SYMBOL(__read_overflow2_field);
>  void __write_overflow_field(size_t avail, size_t wanted) { }
>  EXPORT_SYMBOL(__write_overflow_field);
>  
> -void fortify_panic(const char *name)
> +#define MAKE_FORTIFY_FUNC_NAME(func)	[MAKE_FORTIFY_FUNC(func)] = #func
> +
> +static const char * const fortify_func_name[] = {
> +	EACH_FORTIFY_FUNC(MAKE_FORTIFY_FUNC_NAME)
> +};
> +
> +void __fortify_report(const u8 reason)
> +{
> +	const u8 func = FORTIFY_REASON_FUNC(reason);
> +	const bool write = FORTIFY_REASON_DIR(reason);

Nano-nit: RCT style here :s

> +	const char *name;
> +
> +	name = fortify_func_name[min_t(u8, func, FORTIFY_FUNC_UNKNOWN)];
> +	WARN(1, "%s: detected buffer %s overflow\n", name, str_read_write(!write));
> +}
> +EXPORT_SYMBOL(__fortify_report);
> +
> +void __fortify_panic(const u8 reason)
>  {
> -	pr_emerg("detected buffer overflow in %s\n", name);
> +	__fortify_report(reason);
>  	BUG();
>  }
> -EXPORT_SYMBOL(fortify_panic);
> +EXPORT_SYMBOL(__fortify_panic);
>  #endif /* CONFIG_FORTIFY_SOURCE */

[...]

There's also a small build warning issue. Apart from that, I like how it
does look now, thanks!

Reviewed-by: Alexander Lobakin <aleksander.lobakin@...el.com>

Thanks,
Olek