linux-kernel - Re: [PATCH v3] kcmp: Support selection of SYS_kcmp without CHECKPOINT

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 for Android: free password hash cracker in your pocket

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

Message-ID: <pIyZ-Jj7O2MYk1vKeyghnFmiFWk_5ZWm-Ze1gUqdDaXzImOVjVdjPh2uyHa-sxOPovRk1ApSKk_5zKBvOrzoSwXeXUu0LbZ75Q1D3gIK2Kk=@emersion.fr>
Date:   Fri, 12 Feb 2021 13:14:19 +0000
From:   Simon Ser <contact@...rsion.fr>
To:     Emil Velikov <emil.l.velikov@...il.com>
Cc:     Chris Wilson <chris@...is-wilson.co.uk>,
        Will Drewry <wad@...omium.org>,
        Kees Cook <keescook@...omium.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>,
        Andy Lutomirski <luto@...capital.net>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        "# 3.13+" <stable@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3] kcmp: Support selection of SYS_kcmp without CHECKPOINT_RESTORE

On Friday, February 12th, 2021 at 1:57 PM, Emil Velikov <emil.l.velikov@...il.com> wrote:

> On Fri, 5 Feb 2021 at 22:01, Chris Wilson <chris@...is-wilson.co.uk> wrote:
> >
> > Userspace has discovered the functionality offered by SYS_kcmp and has
> > started to depend upon it. In particular, Mesa uses SYS_kcmp for
> > os_same_file_description() in order to identify when two fd (e.g. device
> > or dmabuf)
>
> As you rightfully point out, SYS_kcmp is a bit of a two edged sword.
> While you mention the CONFIG issue, there is also a portability aspect
> (mesa runs on more than just linux) and as well as sandbox filtering
> of the extra syscall.
>
> Last time I looked, the latter was still an issue and mesa was using
> SYS_kcmp to compare device node fds.
> A far shorter and more portable solution is possible, so let me
> prepare a Mesa patch.

Comparing two DMA-BUFs can be done with their inode number, I think.

Comparing two device FDs is more subtle, because of GEM handle
ref'counting. You sometimes really want to check whether two FDs are
backed by the same file *description*. See [1] for details.

[1]: https://gitlab.freedesktop.org/mesa/drm/-/merge_requests/110