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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