Date: Wed, 25 Mar 2020 13:22:07 -0700 From: Kees Cook <keescook@...omium.org> To: Mark Rutland <mark.rutland@....com> Cc: Thomas Gleixner <tglx@...utronix.de>, 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>, Alexander Potapenko <glider@...gle.com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Jann Horn <jannh@...gle.com>, "Perla, Enrico" <enrico.perla@...el.com>, kernel-hardening@...ts.openwall.com, linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2 5/5] arm64: entry: Enable random_kstack_offset support On Wed, Mar 25, 2020 at 01:21:27PM +0000, Mark Rutland wrote: > On Tue, Mar 24, 2020 at 01:32:31PM -0700, Kees Cook wrote: > > Allow for a randomized stack offset on a per-syscall basis, with roughly > > 5 bits of entropy. > > > > Signed-off-by: Kees Cook <keescook@...omium.org> > > Just to check, do you have an idea of the impact on arm64? Patch 3 had > figures for x86 where it reads the TSC, and it's unclear to me how > get_random_int() compares to that. I didn't do a measurement on arm64 since I don't have a good bare-metal test environment. I know Andy Lutomirki has plans for making get_random_get() as fast as possible, so that's why I used it here. I couldn't figure out if there was a comparable instruction like rdtsc in aarch64 (it seems there's a cycle counter, but I found nothing in the kernel that seemed to actually use it)? > Otherwise, this looks sound to me; I'd jsut like to know whether the > overhead is in the same ballpark. Thanks! -Kees -- Kees Cook
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