From: Kees Cook <keescook@chromium.org>
To: Jann Horn <jannh@google.com>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>,
Alexander Potapenko <glider@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
the arch/x86 maintainers <x86@kernel.org>,
Dave Hansen <dave.hansen@intel.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
sunhaoyl@outlook.com
Subject: Re: [PATCH] fs/binfmt_elf.c: allocate initialized memory in fill_thread_core_info()
Date: Tue, 21 Apr 2020 13:20:58 -0700 [thread overview]
Message-ID: <202004211320.C2B3840@keescook> (raw)
In-Reply-To: <CAG48ez0rWH+kQVFVwwrZHqbL5G5H7CEJ-_xYsF15Wo2RzrqDfg@mail.gmail.com>
On Tue, Apr 21, 2020 at 06:16:25PM +0200, Jann Horn wrote:
> On Tue, Apr 21, 2020 at 6:05 PM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
> > On Tue, 2020-04-21 at 17:09 +0200, Jann Horn wrote:
> > > +x86 folks
> > >
> > > (rest of thread is on lore
> > > <https://lore.kernel.org/lkml/20200419100848.63472-1-glider@google.com/>;,
> > > with original bug report on github
> > > <https://github.com/google/kmsan/issues/76>;)
> > >
> > > On Tue, Apr 21, 2020 at 2:54 PM Alexander Potapenko <glider@google.com> wrote:
> > > > On Tue, Apr 21, 2020 at 5:42 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
> > > > > On Mon, Apr 20, 2020 at 03:41:40PM -0700, Kees Cook wrote:
> > > > > > On Mon, Apr 20, 2020 at 03:33:52PM -0700, Andrew Morton wrote:
> > > > > > > On Sun, 19 Apr 2020 12:08:48 +0200 glider@google.com wrote:
> > > > > > >
> > > > > > > > KMSAN reported uninitialized data being written to disk when dumping
> > > > > > > > core. As a result, several kilobytes of kmalloc memory may be written to
> > > > > > > > the core file and then read by a non-privileged user.
> > > > > >
> > > > > > Ewww. That's been there for 12 years. Did something change in
> > > > > > regset_size() or regset->get()? Do you know what leaves the hole?
> > > > >
> > > > > Not lately and I would also like to hear the details; which regset it is?
> > > > > Should be reasonably easy to find - just memset() the damn thing to something
> > > > > recognizable, do whatever triggers that KMSAN report and look at that
> > > > > resulting coredump.
> > > > >
> > > >
> > > > Seems to be REGSET_XSTATE filled by xstateregs_get().
> > > > Is there a ptrace interface also using that function?
> > >
> > > It looks to me like the problem KMSAN found is that
> > > copy_xstate_to_kernel() will not fill out memory for unused xstates? I
> > > think this may have been introduced by commit 91c3dba7dbc1
> > > ("x86/fpu/xstate: Fix PTRACE frames for XSAVES", introduced in v4.8).
> > >
> > > There seem to be no other functions that reach that path other than
> > > coredumping; I think the correct fix would be to change
> > > copy_xstate_to_kernel() to always fully initialize the output buffer.
> >
> > Yes, that makes sense. On the other hand, the kzalloc() fix prevents potential
> > similar problems for other regsets.
>
> I don't really have anything against using kzalloc() there; but in my
> opinion that's not a fix, that's hardening. The real problem, in my
> opinion, is that regset->get() claims to have filled out a buffer
> without actually having done so; and if someone happens to add another
> caller to that thing in the future, I don't want them to run into
> exactly the same problem again.
Right -- we should fix both.
--
Kees Cook
next prev parent reply other threads:[~2020-04-21 20:21 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-19 10:08 [PATCH] fs/binfmt_elf.c: allocate initialized memory in fill_thread_core_info() glider
2020-04-19 10:10 ` Alexander Potapenko
2020-04-20 22:33 ` Andrew Morton
2020-04-20 22:41 ` Kees Cook
2020-04-21 3:42 ` Al Viro
2020-04-21 8:14 ` Alexander Potapenko
2020-05-12 1:09 ` Al Viro
2020-05-12 3:44 ` Al Viro
2020-05-12 8:20 ` Alexander Potapenko
2020-05-13 3:33 ` Al Viro
2020-05-24 23:45 ` Al Viro
2020-05-26 22:38 ` Al Viro
2020-05-27 12:08 ` Alexander Potapenko
2020-05-27 19:04 ` Borislav Petkov
2020-05-27 19:53 ` Al Viro
2020-05-27 20:09 ` Borislav Petkov
2020-04-21 12:54 ` Alexander Potapenko
2020-04-21 15:09 ` Jann Horn
2020-04-21 16:04 ` Yu-cheng Yu
2020-04-21 16:16 ` Jann Horn
2020-04-21 16:26 ` Yu-cheng Yu
2020-04-21 20:20 ` Kees Cook [this message]
2020-04-21 8:06 ` Alexander Potapenko
2020-05-27 21:55 ` Kees Cook
2020-04-21 8:00 ` Alexander Potapenko
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