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Message-ID: <060292c1-5ce5-0183-8500-c92063351a69@gmail.com>
Date: Wed, 4 Nov 2020 11:02:32 +0200
From: Topi Miettinen <toiwoton@...il.com>
To: Mark Brown <broonie@...nel.org>, Szabolcs Nagy <szabolcs.nagy@....com>
Cc: libc-alpha@...rceware.org, Jeremy Linton <jeremy.linton@....com>,
Catalin Marinas <catalin.marinas@....com>,
Mark Rutland <mark.rutland@....com>, Will Deacon <will@...nel.org>,
Florian Weimer <fweimer@...hat.com>, Kees Cook <keescook@...omium.org>,
Salvatore Mesoraca <s.mesoraca16@...il.com>,
Lennart Poettering <mzxreary@...inter.de>, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, kernel-hardening@...ts.openwall.com,
linux-hardening@...r.kernel.org
Subject: Re: [PATCH 0/4] aarch64: avoid mprotect(PROT_BTI|PROT_EXEC) [BZ
#26831]
On 3.11.2020 19.34, Mark Brown wrote:
> On Tue, Nov 03, 2020 at 10:25:37AM +0000, Szabolcs Nagy wrote:
>
>> Re-mmap executable segments instead of mprotecting them in
>> case mprotect is seccomp filtered.
>
>> For the kernel mapped main executable we don't have the fd
>> for re-mmap so linux needs to be updated to add BTI. (In the
>> presence of seccomp filters for mprotect(PROT_EXEC) the libc
>> cannot change BTI protection at runtime based on user space
>> policy so it is better if the kernel maps BTI compatible
>> binaries with PROT_BTI by default.)
>
> Given that there were still some ongoing discussions on a more robust
> kernel interface here and there seem to be a few concerns with this
> series should we perhaps just take a step back and disable this seccomp
> filter in systemd on arm64, at least for the time being?
Filtering mprotect() and mmap() with seccomp also protects BTI, since
without it the attacker could remove PROT_BTI from existing pages, or
map new pages without BTI. This would be possible even with SARA or
SELinux execmem protections enabled, since they don't care about PROT_BTI.
-Topi
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