lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <ba48e082-3e47-43bc-77d1-97d741c59284@linaro.org>
Date:   Mon, 10 Dec 2018 08:22:06 -0600
From:   Richard Henderson <richard.henderson@...aro.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Kristina Martsenko <kristina.martsenko@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Andrew Jones <drjones@...hat.com>,
        Jacob Bramley <jacob.bramley@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Adam Wallis <awallis@...eaurora.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Will Deacon <will.deacon@....com>,
        Christoffer Dall <christoffer.dall@....com>,
        kvmarm@...ts.cs.columbia.edu, Cyrill Gorcunov <gorcunov@...il.com>,
        Ramana Radhakrishnan <ramana.radhakrishnan@....com>,
        Amit Kachhap <amit.kachhap@....com>,
        Dave P Martin <dave.martin@....com>,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Steve Capper <Steve.Capper@....com>
Subject: Re: [PATCH v6 08/13] arm64: expose user PAC bit positions via ptrace

On 12/10/18 6:03 AM, Catalin Marinas wrote:
>> However, it won't be too long before someone implements support for
>> ARMv8.2-LVA, at which point, without changes to mandatory pointer tagging, we
>> will only have 3 authentication bits: [54:52].  This seems useless and easily
>> brute-force-able.
> 
> Such support is already here (about to be queued):
> 
> https://lore.kernel.org/linux-arm-kernel/20181206225042.11548-1-steve.capper@arm.com/

Thanks for the pointer.

>> Unfortunately, there is no obvious path to making this optional that does not
>> break compatibility with Documentation/arm64/tagged-pointers.txt.
> 
> There is also the ARMv8.5 MTE (memory tagging) which relies on tagged
> pointers.

So it does.  I hadn't read through that extension completely before.

> An alternative would be to allow the opt-in to 52-bit VA, leaving it at
> 48-bit by default. However, it has the problem of changing the PAC size
> and not being able to return.

Perhaps the opt-in should be at exec time, with ELF flags (or equivalent) on
the application.  Because, as you say, changing the shape of the PAC in the
middle of execution is in general not possible.

It isn't perfect, since old kernels won't fail to exec an application setting
flags that can't be supported.  And it requires tooling changes.


r~

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ