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Message-ID: <202103311453.A840B7FC5@keescook>
Date: Wed, 31 Mar 2021 14:54:57 -0700
From: Kees Cook <keescook@...omium.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Elena Reshetova <elena.reshetova@...el.com>, x86@...nel.org,
Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
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 v8 3/6] stack: Optionally randomize kernel stack offset
each syscall
On Wed, Mar 31, 2021 at 09:53:26AM +0200, Thomas Gleixner wrote:
> On Tue, Mar 30 2021 at 13:57, Kees Cook wrote:
> > +/*
> > + * Do not use this anywhere else in the kernel. This is used here because
> > + * it provides an arch-agnostic way to grow the stack with correct
> > + * alignment. Also, since this use is being explicitly masked to a max of
> > + * 10 bits, stack-clash style attacks are unlikely. For more details see
> > + * "VLAs" in Documentation/process/deprecated.rst
> > + * The asm statement is designed to convince the compiler to keep the
> > + * allocation around even after "ptr" goes out of scope.
>
> Nit. That explanation of "ptr" might be better placed right at the
> add_random...() macro.
Ah, yes! Fixed in v9.
> Other than that.
>
> Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Thank you for the reviews!
Do you want to take this via -tip (and leave off the arm64 patch until
it is acked), or would you rather it go via arm64? (I've sent v9 now...)
--
Kees Cook
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