From: Florian Weimer <fweimer@redhat.com>
To: Will Deacon <will@kernel.org>
Cc: Mark Brown <broonie@kernel.org>,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
libc-alpha@sourceware.org, Jeremy Linton <jeremy.linton@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Kees Cook <keescook@chromium.org>,
Salvatore Mesoraca <s.mesoraca16@gmail.com>,
Lennart Poettering <mzxreary@0pointer.de>,
Topi Miettinen <toiwoton@gmail.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
kernel-hardening@lists.openwall.com,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH 0/4] aarch64: avoid mprotect(PROT_BTI|PROT_EXEC) [BZ #26831]
Date: Wed, 04 Nov 2020 10:29:29 +0100 [thread overview]
Message-ID: <87h7q54ghy.fsf@oldenburg2.str.redhat.com> (raw)
In-Reply-To: <20201104092012.GA6439@willie-the-truck> (Will Deacon's message of "Wed, 4 Nov 2020 09:20:12 +0000")
* Will Deacon:
> Is there real value in this seccomp filter if it only looks at mprotect(),
> or was it just implemented because it's easy to do and sounds like a good
> idea?
It seems bogus to me. Everyone will just create alias mappings instead,
just like they did for the similar SELinux feature. See “Example code
to avoid execmem violations” in:
<https://www.akkadia.org/drepper/selinux-mem.html>
As you can see, this reference implementation creates a PROT_WRITE
mapping aliased to a PROT_EXEC mapping, so it actually reduces security
compared to something that generates the code in an anonymous mapping
and calls mprotect to make it executable.
Furthermore, it requires unusual cache flushing code on some AArch64
implementations (a requirement that is not shared by any Linux other
architecture to which libffi has been ported), resulting in
hard-to-track-down real-world bugs.
Thanks,
Florian
--
Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn,
Commercial register: Amtsgericht Muenchen, HRB 153243,
Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill
WARNING: multiple messages have this Message-ID (diff)
From: Florian Weimer <fweimer@redhat.com>
To: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
Salvatore Mesoraca <s.mesoraca16@gmail.com>,
libc-alpha@sourceware.org, Kees Cook <keescook@chromium.org>,
kernel-hardening@lists.openwall.com,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
linux-kernel@vger.kernel.org,
Jeremy Linton <jeremy.linton@arm.com>,
Mark Brown <broonie@kernel.org>,
Lennart Poettering <mzxreary@0pointer.de>,
linux-hardening@vger.kernel.org,
Topi Miettinen <toiwoton@gmail.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 0/4] aarch64: avoid mprotect(PROT_BTI|PROT_EXEC) [BZ #26831]
Date: Wed, 04 Nov 2020 10:29:29 +0100 [thread overview]
Message-ID: <87h7q54ghy.fsf@oldenburg2.str.redhat.com> (raw)
In-Reply-To: <20201104092012.GA6439@willie-the-truck> (Will Deacon's message of "Wed, 4 Nov 2020 09:20:12 +0000")
* Will Deacon:
> Is there real value in this seccomp filter if it only looks at mprotect(),
> or was it just implemented because it's easy to do and sounds like a good
> idea?
It seems bogus to me. Everyone will just create alias mappings instead,
just like they did for the similar SELinux feature. See “Example code
to avoid execmem violations” in:
<https://www.akkadia.org/drepper/selinux-mem.html>
As you can see, this reference implementation creates a PROT_WRITE
mapping aliased to a PROT_EXEC mapping, so it actually reduces security
compared to something that generates the code in an anonymous mapping
and calls mprotect to make it executable.
Furthermore, it requires unusual cache flushing code on some AArch64
implementations (a requirement that is not shared by any Linux other
architecture to which libffi has been ported), resulting in
hard-to-track-down real-world bugs.
Thanks,
Florian
--
Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn,
Commercial register: Amtsgericht Muenchen, HRB 153243,
Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill
_______________________________________________
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:[~2020-11-04 9:29 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-03 10:25 [PATCH 0/4] aarch64: avoid mprotect(PROT_BTI|PROT_EXEC) [BZ #26831] Szabolcs Nagy
2020-11-03 10:25 ` Szabolcs Nagy
2020-11-03 10:25 ` [PATCH 1/4] elf: Pass the fd to note processing " Szabolcs Nagy
2020-11-03 10:25 ` Szabolcs Nagy
2020-11-03 10:26 ` [PATCH 2/4] elf: Move note processing after l_phdr is updated " Szabolcs Nagy
2020-11-03 10:26 ` Szabolcs Nagy
2020-11-03 10:38 ` Florian Weimer
2020-11-03 10:38 ` Florian Weimer
2020-11-03 10:38 ` Florian Weimer
2020-11-03 12:36 ` H.J. Lu
2020-11-03 12:36 ` H.J. Lu
2020-11-03 12:36 ` H.J. Lu
2020-11-03 15:04 ` Szabolcs Nagy
2020-11-03 15:04 ` Szabolcs Nagy
2020-11-03 15:27 ` H.J. Lu
2020-11-03 15:27 ` H.J. Lu
2020-11-03 15:27 ` H.J. Lu
2020-11-03 10:26 ` [PATCH 3/4] aarch64: Use mmap to add PROT_BTI instead of mprotect " Szabolcs Nagy
2020-11-03 10:26 ` Szabolcs Nagy
2020-11-03 10:34 ` Florian Weimer
2020-11-03 10:34 ` Florian Weimer
2020-11-03 10:34 ` Florian Weimer
2020-11-03 10:26 ` [PATCH 4/4] aarch64: Remove the bti link_map field " Szabolcs Nagy
2020-11-03 10:26 ` Szabolcs Nagy
2020-11-03 17:34 ` [PATCH 0/4] aarch64: avoid mprotect(PROT_BTI|PROT_EXEC) " Mark Brown
2020-11-03 17:34 ` Mark Brown
2020-11-04 5:41 ` Jeremy Linton
2020-11-04 5:41 ` Jeremy Linton
2020-11-04 8:57 ` Szabolcs Nagy
2020-11-04 8:57 ` Szabolcs Nagy
2020-11-04 14:41 ` Catalin Marinas
2020-11-04 14:41 ` Catalin Marinas
2020-11-04 14:45 ` Florian Weimer
2020-11-04 14:45 ` Florian Weimer
2020-11-04 14:45 ` Florian Weimer
2020-11-04 10:50 ` Mark Brown
2020-11-04 10:50 ` Mark Brown
2020-11-04 18:47 ` Jeremy Linton
2020-11-04 18:47 ` Jeremy Linton
2020-11-04 18:53 ` Mark Brown
2020-11-04 18:53 ` Mark Brown
2020-11-04 9:02 ` Topi Miettinen
2020-11-04 9:02 ` Topi Miettinen
2020-11-04 9:20 ` Will Deacon
2020-11-04 9:20 ` Will Deacon
2020-11-04 9:29 ` Florian Weimer [this message]
2020-11-04 9:29 ` Florian Weimer
2020-11-04 9:29 ` Florian Weimer
2020-11-04 9:55 ` Topi Miettinen
2020-11-04 9:55 ` Topi Miettinen
2020-11-04 14:35 ` Catalin Marinas
2020-11-04 14:35 ` Catalin Marinas
2020-11-04 15:19 ` Topi Miettinen
2020-11-04 15:19 ` Topi Miettinen
2020-11-04 16:08 ` Szabolcs Nagy
2020-11-04 16:08 ` Szabolcs Nagy
2020-11-04 15:20 ` Mark Rutland
2020-11-04 15:20 ` Mark Rutland
2020-11-04 18:59 ` Jeremy Linton
2020-11-04 18:59 ` Jeremy Linton
2020-11-05 11:31 ` Szabolcs Nagy
2020-11-05 11:31 ` Szabolcs Nagy
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