linux-kernel - Re: [RFC PATCH v19 1/5] exec: Add a new AT

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]

Message-ID: <20240709.aa5ahChoo7No@digikod.net>
Date: Tue, 9 Jul 2024 22:42:26 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: Florian Weimer <fweimer@...hat.com>
Cc: Jeff Xu <jeffxu@...gle.com>, Al Viro <viro@...iv.linux.org.uk>, 
	Christian Brauner <brauner@...nel.org>, Kees Cook <keescook@...omium.org>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, Paul Moore <paul@...l-moore.com>, Theodore Ts'o <tytso@....edu>, 
	Alejandro Colomar <alx@...nel.org>, Aleksa Sarai <cyphar@...har.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	Casey Schaufler <casey@...aufler-ca.com>, Christian Heimes <christian@...hon.org>, 
	Dmitry Vyukov <dvyukov@...gle.com>, Eric Biggers <ebiggers@...nel.org>, 
	Eric Chiang <ericchiang@...gle.com>, Fan Wu <wufan@...ux.microsoft.com>, 
	Geert Uytterhoeven <geert@...ux-m68k.org>, James Morris <jamorris@...ux.microsoft.com>, 
	Jan Kara <jack@...e.cz>, Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>, 
	Jordan R Abrahams <ajordanr@...gle.com>, Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>, 
	Luca Boccassi <bluca@...ian.org>, Luis Chamberlain <mcgrof@...nel.org>, 
	"Madhavan T . Venkataraman" <madvenka@...ux.microsoft.com>, Matt Bobrowski <mattbobrowski@...gle.com>, 
	Matthew Garrett <mjg59@...f.ucam.org>, Matthew Wilcox <willy@...radead.org>, 
	Miklos Szeredi <mszeredi@...hat.com>, Mimi Zohar <zohar@...ux.ibm.com>, 
	Nicolas Bouchinet <nicolas.bouchinet@....gouv.fr>, Scott Shell <scottsh@...rosoft.com>, 
	Shuah Khan <shuah@...nel.org>, Stephen Rothwell <sfr@...b.auug.org.au>, 
	Steve Dower <steve.dower@...hon.org>, Steve Grubb <sgrubb@...hat.com>, 
	Thibaut Sautereau <thibaut.sautereau@....gouv.fr>, Vincent Strubel <vincent.strubel@....gouv.fr>, 
	Xiaoming Ni <nixiaoming@...wei.com>, Yin Fengwei <fengwei.yin@...el.com>, 
	kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-security-module@...r.kernel.org
Subject: Re: [RFC PATCH v19 1/5] exec: Add a new AT_CHECK flag to execveat(2)

On Tue, Jul 09, 2024 at 12:05:50PM +0200, Florian Weimer wrote:
> * Mickaël Salaün:
> 
> >> > If we want to avoid that, we could have an agreed-upon error code which
> >> > the LSM can signal that it'll never fail AT_CHECK checks, so we only
> >> > have to perform the extra system call once.
> >
> > I'm not sure to follow.  Either we check executable code or we don't,
> > but it doesn't make sense to only check some parts (except for migration
> > of user space code in a system, which is one purpose of the securebits
> > added with the next patch).
> >
> > The idea with AT_CHECK is to unconditionnaly check executable right the
> > same way it is checked when a file is executed.  User space can decide
> > to check that or not according to its policy (i.e. securebits).
> 
> I meant it purely as a performance optimization, to skip future system
> calls if we know they won't provide any useful information for this
> process.  In the grand scheme of things, the extra system call probably
> does not matter because we already have to do costly things like mmap.

Indeed, the performance impact of execveat+AT_CHECK should be negligible
compared to everything else needed to interpret a script or spawn a
process.  Moreover, these checks should only be performed when
SECBIT_SHOULD_EXEC_CHECK is set for the caller.