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

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Date:   Thu, 1 Apr 2021 09:37:59 +0100
From:   Will Deacon <will@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        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

Hi Kees,

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

https://lore.kernel.org/r/20210401083034.GA8554@willie-the-truck
https://lore.kernel.org/r/20210401083430.GB8554@willie-the-truck

Will