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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

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  reply	other threads:[~2020-10-22 20:03 UTC|newest]

Thread overview: 38+ 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  7:54   ` Florian Weimer
2020-10-22  8:17     ` Topi Miettinen
2020-10-22  8:25       ` Florian Weimer
2020-10-22  8:29       ` Szabolcs Nagy
2020-10-22  8:38         ` Lennart Poettering
2020-10-22  9:31           ` Catalin Marinas
2020-10-22 10:12             ` Topi Miettinen
2020-10-22 10:27               ` Florian Weimer
2020-10-23  6:13             ` Szabolcs Nagy
2020-10-23  9:04               ` Catalin Marinas
2020-10-22 10:03         ` Topi Miettinen
2020-10-22  8:05   ` Szabolcs Nagy
2020-10-22  8:31     ` Lennart Poettering
     [not found] ` <20201022075447.GO3819@arm.com>
2020-10-22 10:39   ` Topi Miettinen
2020-10-22 20:02     ` Kees Cook [this message]
2020-10-22 22:24       ` Topi Miettinen
2020-10-23 17:52         ` Salvatore Mesoraca
2020-10-24 11:34           ` Topi Miettinen
2020-10-24 14:12             ` Salvatore Mesoraca
2020-10-25 13:42               ` Jordan Glover
2020-10-23  9:02       ` Catalin Marinas
2020-10-24 11:01         ` Topi Miettinen
2020-10-26 14:52           ` Catalin Marinas
2020-10-26 15:56             ` Dave Martin
2020-10-26 16:51               ` Mark Brown
2020-10-26 16:31             ` Topi Miettinen
2020-10-26 16:24 ` Dave Martin
2020-10-26 16:39   ` Topi Miettinen
2020-10-26 16:45   ` Florian Weimer
2020-10-27 14:22     ` Dave Martin
2020-10-27 14:41       ` Florian Weimer
2020-10-26 16:57   ` Szabolcs Nagy
2020-10-26 17:52     ` Dave Martin
2020-10-26 22:39       ` Jeremy Linton
2020-10-27 14:15         ` Dave Martin
2020-10-29 11:02           ` Catalin Marinas
2020-11-04 12:18             ` Dave Martin

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