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From: Florian Weimer <fweimer@redhat.com>
To: Topi Miettinen <toiwoton@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Lennart Poettering <mzxreary@0pointer.de>,
	Szabolcs Nagy <szabolcs.nagy@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	systemd-devel@lists.freedesktop.org,
	Kees Cook <keescook@chromium.org>,
	Will Deacon <will.deacon@arm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Mark Brown <broonie@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: [systemd-devel] BTI interaction between seccomp filters in systemd and glibc mprotect calls, causing service failures
Date: Thu, 22 Oct 2020 12:27:00 +0200	[thread overview]
Message-ID: <875z72r1xn.fsf@oldenburg2.str.redhat.com> (raw)
In-Reply-To: <4e82e730-4e71-35fe-e46e-f032766dedeb@gmail.com> (Topi Miettinen's message of "Thu, 22 Oct 2020 13:12:09 +0300")

* Topi Miettinen:

> Allowing mprotect(PROT_EXEC|PROT_BTI) would mean that all you need to
> circumvent MDWX is to add PROT_BTI flag. I'd suggest getting the flags 
> right at mmap() time or failing that, reverting the PROT_BTI for
> legacy programs later.
>
> Could the kernel tell the loader of the BTI situation with auxiliary
> vectors? Then it would be easy for the loader to always use the best 
> mmap() flags without ever needing to mprotect().

I think what we want is a mprotect2 call with a flags argument (separate
from protection flags) that tells the kernel that the request *removes*
protection flags and should fail otherwise.  seccomp could easily filter
that then.

But like the other proposals, the migration story isn't great.  You
would need kernel and seccomp/systemd etc. updates before glibc starts
working, even if glibc has a fallback from mprotect2 to mprotect
(because the latter would be blocked).

Thanks,
Florian
-- 
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Commercial register: Amtsgericht Muenchen, HRB 153243,
Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill


  reply	other threads:[~2020-10-22 10:27 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 [this message]
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
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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