From: Kees Cook <keescook@chromium.org>
To: Topi Miettinen <toiwoton@gmail.com>
Cc: Szabolcs Nagy <szabolcs.nagy@arm.com>,
Jeremy Linton <jeremy.linton@arm.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
libc-alpha@sourceware.org, systemd-devel@lists.freedesktop.org,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Mark Brown <broonie@kernel.org>,
Dave Martin <dave.martin@arm.com>,
Catalin Marinas <Catalin.Marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Salvatore Mesoraca <s.mesoraca16@gmail.com>,
kernel-hardening@lists.openwall.com,
linux-hardening@vger.kernel.org
Subject: Re: BTI interaction between seccomp filters in systemd and glibc mprotect calls, causing service failures
Date: Thu, 22 Oct 2020 13:02:18 -0700 [thread overview]
Message-ID: <202010221256.A4F95FD11@keescook> (raw)
In-Reply-To: <78464155-f459-773f-d0ee-c5bdbeb39e5d@gmail.com>
On Thu, Oct 22, 2020 at 01:39:07PM +0300, Topi Miettinen wrote:
> But I think SELinux has a more complete solution (execmem) which can track
> the pages better than is possible with seccomp solution which has a very
> narrow field of view. Maybe this facility could be made available to
> non-SELinux systems, for example with prctl()? Then the in-kernel MDWX could
> allow mprotect(PROT_EXEC | PROT_BTI) in case the backing file hasn't been
> modified, the source filesystem isn't writable for the calling process and
> the file descriptor isn't created with memfd_create().
Right. The problem here is that systemd is attempting to mediate a
state change using only syscall details (i.e. with seccomp) instead of
a stateful analysis. Using a MAC is likely the only sane way to do that.
SELinux is a bit difficult to adjust "on the fly" the way systemd would
like to do things, and the more dynamic approach seen with SARA[1] isn't
yet in the kernel. Trying to enforce memory W^X protection correctly
via seccomp isn't really going to work well, as far as I can see.
Regardless, it makes sense to me to have the kernel load the executable
itself with BTI enabled by default. I prefer gaining Catalin's suggested
patch[2]. :)
[1] https://lore.kernel.org/kernel-hardening/1562410493-8661-1-git-send-email-s.mesoraca16@gmail.com/
[2] https://lore.kernel.org/linux-arm-kernel/20201022093104.GB1229@gaia/
--
Kees Cook
WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org>
To: Topi Miettinen <toiwoton@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
Salvatore Mesoraca <s.mesoraca16@gmail.com>,
systemd-devel@lists.freedesktop.org,
kernel-hardening@lists.openwall.com,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
Catalin Marinas <Catalin.Marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Jeremy Linton <jeremy.linton@arm.com>,
Mark Brown <broonie@kernel.org>,
linux-hardening@vger.kernel.org, libc-alpha@sourceware.org,
Dave Martin <dave.martin@arm.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: BTI interaction between seccomp filters in systemd and glibc mprotect calls, causing service failures
Date: Thu, 22 Oct 2020 13:02:18 -0700 [thread overview]
Message-ID: <202010221256.A4F95FD11@keescook> (raw)
In-Reply-To: <78464155-f459-773f-d0ee-c5bdbeb39e5d@gmail.com>
On Thu, Oct 22, 2020 at 01:39:07PM +0300, Topi Miettinen wrote:
> But I think SELinux has a more complete solution (execmem) which can track
> the pages better than is possible with seccomp solution which has a very
> narrow field of view. Maybe this facility could be made available to
> non-SELinux systems, for example with prctl()? Then the in-kernel MDWX could
> allow mprotect(PROT_EXEC | PROT_BTI) in case the backing file hasn't been
> modified, the source filesystem isn't writable for the calling process and
> the file descriptor isn't created with memfd_create().
Right. The problem here is that systemd is attempting to mediate a
state change using only syscall details (i.e. with seccomp) instead of
a stateful analysis. Using a MAC is likely the only sane way to do that.
SELinux is a bit difficult to adjust "on the fly" the way systemd would
like to do things, and the more dynamic approach seen with SARA[1] isn't
yet in the kernel. Trying to enforce memory W^X protection correctly
via seccomp isn't really going to work well, as far as I can see.
Regardless, it makes sense to me to have the kernel load the executable
itself with BTI enabled by default. I prefer gaining Catalin's suggested
patch[2]. :)
[1] https://lore.kernel.org/kernel-hardening/1562410493-8661-1-git-send-email-s.mesoraca16@gmail.com/
[2] https://lore.kernel.org/linux-arm-kernel/20201022093104.GB1229@gaia/
--
Kees Cook
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-10-22 20:02 UTC|newest]
Thread overview: 88+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <8584c14f-5c28-9d70-c054-7c78127d84ea@arm.com>
2020-10-22 7:18 ` [systemd-devel] BTI interaction between seccomp filters in systemd and glibc mprotect calls, causing service failures Lennart Poettering
2020-10-22 7:18 ` Lennart Poettering
2020-10-22 7:54 ` Florian Weimer
2020-10-22 7:54 ` Florian Weimer
2020-10-22 8:17 ` Topi Miettinen
2020-10-22 8:17 ` Topi Miettinen
2020-10-22 8:25 ` Florian Weimer
2020-10-22 8:25 ` Florian Weimer
2020-10-22 8:29 ` Szabolcs Nagy
2020-10-22 8:29 ` Szabolcs Nagy
2020-10-22 8:38 ` Lennart Poettering
2020-10-22 8:38 ` Lennart Poettering
2020-10-22 9:31 ` Catalin Marinas
2020-10-22 9:31 ` Catalin Marinas
2020-10-22 10:12 ` Topi Miettinen
2020-10-22 10:12 ` Topi Miettinen
2020-10-22 10:27 ` Florian Weimer
2020-10-22 10:27 ` Florian Weimer
2020-10-23 6:13 ` Szabolcs Nagy
2020-10-23 6:13 ` Szabolcs Nagy
2020-10-23 9:04 ` Catalin Marinas
2020-10-23 9:04 ` Catalin Marinas
2020-10-22 10:03 ` Topi Miettinen
2020-10-22 10:03 ` Topi Miettinen
2020-10-22 8:05 ` Szabolcs Nagy
2020-10-22 8:05 ` Szabolcs Nagy
2020-10-22 8:31 ` Lennart Poettering
2020-10-22 8:31 ` Lennart Poettering
[not found] ` <20201022075447.GO3819@arm.com>
2020-10-22 10:39 ` Topi Miettinen
2020-10-22 10:39 ` Topi Miettinen
2020-10-22 20:02 ` Kees Cook [this message]
2020-10-22 20:02 ` Kees Cook
2020-10-22 20:02 ` Kees Cook
2020-10-22 22:24 ` Topi Miettinen
2020-10-22 22:24 ` Topi Miettinen
2020-10-22 22:24 ` Topi Miettinen
2020-10-23 17:52 ` Salvatore Mesoraca
2020-10-23 17:52 ` Salvatore Mesoraca
2020-10-23 17:52 ` Salvatore Mesoraca
2020-10-24 11:34 ` Topi Miettinen
2020-10-24 11:34 ` Topi Miettinen
2020-10-24 11:34 ` Topi Miettinen
2020-10-24 14:12 ` Salvatore Mesoraca
2020-10-24 14:12 ` Salvatore Mesoraca
2020-10-24 14:12 ` Salvatore Mesoraca
2020-10-25 13:42 ` Jordan Glover
2020-10-25 13:42 ` Jordan Glover
2020-10-25 13:42 ` Jordan Glover
2020-10-23 9:02 ` Catalin Marinas
2020-10-23 9:02 ` Catalin Marinas
2020-10-23 9:02 ` Catalin Marinas
2020-10-24 11:01 ` Topi Miettinen
2020-10-24 11:01 ` Topi Miettinen
2020-10-24 11:01 ` Topi Miettinen
2020-10-26 14:52 ` Catalin Marinas
2020-10-26 14:52 ` Catalin Marinas
2020-10-26 14:52 ` Catalin Marinas
2020-10-26 15:56 ` Dave Martin
2020-10-26 15:56 ` Dave Martin
2020-10-26 15:56 ` Dave Martin
2020-10-26 16:51 ` Mark Brown
2020-10-26 16:51 ` Mark Brown
2020-10-26 16:51 ` Mark Brown
2020-10-26 16:31 ` Topi Miettinen
2020-10-26 16:31 ` Topi Miettinen
2020-10-26 16:31 ` Topi Miettinen
2020-10-26 16:24 ` Dave Martin
2020-10-26 16:24 ` Dave Martin
2020-10-26 16:39 ` Topi Miettinen
2020-10-26 16:39 ` Topi Miettinen
2020-10-26 16:45 ` Florian Weimer
2020-10-26 16:45 ` Florian Weimer
2020-10-27 14:22 ` Dave Martin
2020-10-27 14:22 ` Dave Martin
2020-10-27 14:41 ` Florian Weimer
2020-10-27 14:41 ` Florian Weimer
2020-10-26 16:57 ` Szabolcs Nagy
2020-10-26 16:57 ` Szabolcs Nagy
2020-10-26 17:52 ` Dave Martin
2020-10-26 17:52 ` Dave Martin
2020-10-26 22:39 ` Jeremy Linton
2020-10-26 22:39 ` Jeremy Linton
2020-10-27 14:15 ` Dave Martin
2020-10-27 14:15 ` Dave Martin
2020-10-29 11:02 ` Catalin Marinas
2020-10-29 11:02 ` Catalin Marinas
2020-11-04 12:18 ` Dave Martin
2020-11-04 12:18 ` Dave Martin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=202010221256.A4F95FD11@keescook \
--to=keescook@chromium.org \
--cc=Catalin.Marinas@arm.com \
--cc=broonie@kernel.org \
--cc=dave.martin@arm.com \
--cc=jeremy.linton@arm.com \
--cc=kernel-hardening@lists.openwall.com \
--cc=libc-alpha@sourceware.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-hardening@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=s.mesoraca16@gmail.com \
--cc=systemd-devel@lists.freedesktop.org \
--cc=szabolcs.nagy@arm.com \
--cc=toiwoton@gmail.com \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.