Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Wed, 4 Nov 2020 11:02:32 +0200
From: Topi Miettinen <>
To: Mark Brown <>, Szabolcs Nagy <>
Cc:, Jeremy Linton <>,
 Catalin Marinas <>,
 Mark Rutland <>, Will Deacon <>,
 Florian Weimer <>, Kees Cook <>,
 Salvatore Mesoraca <>,
 Lennart Poettering <>,,,,
Subject: Re: [PATCH 0/4] aarch64: avoid mprotect(PROT_BTI|PROT_EXEC) [BZ

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.


Powered by blists - more mailing lists

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.