linux-hardening - Re: [PATCH v9 0/6] Optionally randomize kernel stack offset each syscall

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Message-ID: <87sg4a3zap.ffs@nanos.tec.linutronix.de>
Date:   Thu, 01 Apr 2021 15:33:02 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Will Deacon <will@...nel.org>, Kees Cook <keescook@...omium.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Elena Reshetova <elena.reshetova@...el.com>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexander Potapenko <glider@...gle.com>,
        Alexander Popov <alex.popov@...ux.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jann Horn <jannh@...gle.com>, Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Randy Dunlap <rdunlap@...radead.org>,
        kernel-hardening@...ts.openwall.com,
        linux-hardening@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 0/6] Optionally randomize kernel stack offset each syscall

On Thu, Apr 01 2021 at 09:37, Will Deacon wrote:
> On Wed, Mar 31, 2021 at 01:54:52PM -0700, Kees Cook wrote:
>> Hi Will (and Mark and Catalin),
>> 
>> Can you take this via the arm64 tree for v5.13 please? Thomas has added
>> his Reviewed-by, so it only leaves arm64's. :)
>
> Sorry, these got mixed up in my inbox so I just replied to v7 and v8 and
> then noticed v9. Argh!
>
> However, I think the comments still apply: namely that the dummy "=m" looks
> dangerous to me

> https://lore.kernel.org/r/20210401083034.GA8554@willie-the-truck

Hrmpf, didn't think about that.

> and I think you're accessing pcpu variables with preemption enabled
> for the arm64 part:

That's my fault. On x86 this is invoked right after coming up into C
code and _before_ enabling interrupts, which I why I suggested not to
use the wrapped one. raw_cpu_read() should be fine everywhere.

Thanks,

        tglx