linux-kernel - Re: [PATCH v2] lib/string.c: implement stpcpy

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 14 Aug 2020 20:42:35 -0700
From:   Joe Perches <joe@...ches.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Dávid Bolvanský <david.bolvansky@...il.com>,
        Eli Friedman <efriedma@...cinc.com>, stable@...r.kernel.org,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Daniel Axtens <dja@...ens.net>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...nel.org>,
        Yury Norov <yury.norov@...il.com>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH v2] lib/string.c: implement stpcpy

On Fri, 2020-08-14 at 19:09 -0700, Nick Desaulniers wrote:
> LLVM implemented a recent "libcall optimization" that lowers calls to
> `sprintf(dest, "%s", str)` where the return value is used to
> `stpcpy(dest, str) - dest`. This generally avoids the machinery involved
> in parsing format strings.  Calling `sprintf` with overlapping arguments
> was clarified in ISO C99 and POSIX.1-2001 to be undefined behavior.
> 
> `stpcpy` is just like `strcpy` except it returns the pointer to the new
> tail of `dest`. This allows you to chain multiple calls to `stpcpy` in
> one statement.
[]
> diff --git a/include/linux/string.h b/include/linux/string.h
[]
> @@ -31,6 +31,9 @@ size_t strlcpy(char *, const char *, size_t);
>  #ifndef __HAVE_ARCH_STRSCPY
>  ssize_t strscpy(char *, const char *, size_t);
>  #endif
> +#ifndef __HAVE_ARCH_STPCPY
> +extern char *stpcpy(char *__restrict__, const char *__restrict__);

If __restrict__ is used, perhaps it should follow the
kernel style used by attributes like __iomem and __user

extern char *stpcpy(char __restrict *dest, const char __restrict *src);

(though I would lose the extern too)

char *stpcpy(char __restrict *dest, const char __restrict *src);