linux-kernel - Re: [PATCH v4 0/3] Fix bugs and performance of kstack offset randomisation

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Message-ID: <C502BCE6-2FB2-4A06-93A8-E8DEDFC22914@kernel.org>
Date: Mon, 19 Jan 2026 08:44:17 -0800
From: Kees Cook <kees@...nel.org>
To: Dave Hansen <dave.hansen@...el.com>, Ryan Roberts <ryan.roberts@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Huacai Chen <chenhuacai@...nel.org>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>, Paul Walmsley <pjw@...nel.org>,
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 Mark Rutland <mark.rutland@....com>, "Jason A. Donenfeld" <Jason@...c4.com>,
 Ard Biesheuvel <ardb@...nel.org>, Jeremy Linton <jeremy.linton@....com>,
 David Laight <david.laight.linux@...il.com>
CC: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 loongarch@...ts.linux.dev, linuxppc-dev@...ts.ozlabs.org,
 linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4 0/3] Fix bugs and performance of kstack offset randomisation

On January 19, 2026 8:00:00 AM PST, Dave Hansen <dave.hansen@...el.com> wrote:
>On 1/19/26 05:01, Ryan Roberts wrote:
>> x86 (AWS Sapphire Rapids):
>> +-----------------+--------------+-------------+---------------+
>> | Benchmark       | Result Class |   v6.18-rc5 | per-task-prng |
>> |                 |              | rndstack-on |               |
>> |                 |              |             |               |
>> +=================+==============+=============+===============+
>> | syscall/getpid  | mean (ns)    |  (R) 13.32% |     (R) 4.60% |
>> |                 | p99 (ns)     |  (R) 13.38% |    (R) 18.08% |
>> |                 | p99.9 (ns)   |      16.26% |    (R) 19.38% |
>
>Like you noted, this is surprising. This would be a good thing to make
>sure it goes in very early after -rc1 and gets plenty of wide testing.

Right, we are pretty late in the dev cycle (rc6). It would be prudent to get this into -next after the coming rc1 (1 month from now).

On the other hand, the changes are pretty "binary" in the sense that mistakes should be VERY visible right away. Would it be better to take this into -next immediately instead?

>But I don't see any problems with the approach, and the move to common
>code looks like a big win as well:

Agreed; I think it's looking great.

-- 
Kees Cook