linux-kernel - Re: [PATCH v2 1/7] binfmt: don't use MAP_DENYWRITE when loading shared libraries via uselib()

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Message-ID: <20210905153229.GA3019909@roeck-us.net>
Date:   Sun, 5 Sep 2021 08:32:29 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Kees Cook <keescook@...omium.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Mike Rapoport <rppt@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Chinwen Chang <chinwen.chang@...iatek.com>,
        Catalin Marinas <catalin.marinas@....com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Huang Ying <ying.huang@...el.com>,
        Jann Horn <jannh@...gle.com>, Feng Tang <feng.tang@...el.com>,
        Kevin Brodsky <Kevin.Brodsky@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Shawn Anastasio <shawn@...stas.io>,
        Steven Price <steven.price@....com>,
        Nicholas Piggin <npiggin@...il.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Jens Axboe <axboe@...nel.dk>,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        Peter Xu <peterx@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Nicolas Viennot <Nicolas.Viennot@...sigma.com>,
        Thomas Cedeno <thomascedeno@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Chengguang Xu <cgxu519@...ernel.net>,
        Christian König 
        <ckoenig.leichtzumerken@...il.com>,
        Florian Weimer <fweimer@...hat.com>,
        David Laight <David.Laight@...LAB.COM>,
        linux-unionfs@...r.kernel.org, linux-api@...r.kernel.org,
        x86@...nel.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 1/7] binfmt: don't use MAP_DENYWRITE when loading
 shared libraries via uselib()

On Mon, Aug 16, 2021 at 09:48:34PM +0200, David Hildenbrand wrote:
> uselib() is the legacy systemcall for loading shared libraries.
> Nowadays, applications use dlopen() to load shared libraries, completely
> implemented in user space via mmap().
> 
> For example, glibc uses MAP_COPY to mmap shared libraries. While this
> maps to MAP_PRIVATE | MAP_DENYWRITE on Linux, Linux ignores any
> MAP_DENYWRITE specification from user space in mmap.
> 
> With this change, all remaining in-tree users of MAP_DENYWRITE use it
> to map an executable. We will be able to open shared libraries loaded
> via uselib() writable, just as we already can via dlopen() from user
> space.
> 
> This is one step into the direction of removing MAP_DENYWRITE from the
> kernel. This can be considered a minor user space visible change.
> 
> Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  arch/x86/ia32/ia32_aout.c | 2 +-
>  fs/binfmt_aout.c          | 2 +-
>  fs/binfmt_elf.c           | 2 +-
>  3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/ia32/ia32_aout.c b/arch/x86/ia32/ia32_aout.c
> index 5e5b9fc2747f..321d7b22ad2d 100644
> --- a/arch/x86/ia32/ia32_aout.c
> +++ b/arch/x86/ia32/ia32_aout.c
> @@ -293,7 +293,7 @@ static int load_aout_library(struct file *file)
>  	/* Now use mmap to map the library into memory. */
>  	error = vm_mmap(file, start_addr, ex.a_text + ex.a_data,
>  			PROT_READ | PROT_WRITE | PROT_EXEC,
> -			MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE | MAP_32BIT,
> +			MAP_FIXED | MAP_PRIVATE | MAP_32BIT,
>  			N_TXTOFF(ex));
>  	retval = error;
>  	if (error != start_addr)
> diff --git a/fs/binfmt_aout.c b/fs/binfmt_aout.c
> index 145917f734fe..d29de971d3f3 100644
> --- a/fs/binfmt_aout.c
> +++ b/fs/binfmt_aout.c
> @@ -309,7 +309,7 @@ static int load_aout_library(struct file *file)
>  	/* Now use mmap to map the library into memory. */
>  	error = vm_mmap(file, start_addr, ex.a_text + ex.a_data,
>  			PROT_READ | PROT_WRITE | PROT_EXEC,
> -			MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE,
> +			MAP_FIXED | MAP_PRIVATE;
>  			N_TXTOFF(ex));

Guess someone didn't care compile testing their code. This is now in
mainline.

Guenter