From: Kees Cook <kees@kernel.org>
To: Ryan Roberts <ryan.roberts@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Huacai Chen <chenhuacai@kernel.org>,
Madhavan Srinivasan <maddy@linux.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Paul Walmsley <pjw@kernel.org>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Heiko Carstens <hca@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
Mark Rutland <mark.rutland@arm.com>,
"Jason A. Donenfeld" <Jason@zx2c4.com>,
Ard Biesheuvel <ardb@kernel.org>,
Jeremy Linton <jeremy.linton@arm.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev,
linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
linux-s390@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH v2 3/3] randomize_kstack: Unify random source across arches
Date: Tue, 16 Dec 2025 00:27:38 -0800 [thread overview]
Message-ID: <202512160024.B688A8D0@keescook> (raw)
In-Reply-To: <20251215163520.1144179-4-ryan.roberts@arm.com>
On Mon, Dec 15, 2025 at 04:35:17PM +0000, Ryan Roberts wrote:
> [...]
> @@ -45,9 +46,22 @@ DECLARE_STATIC_KEY_MAYBE(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT,
> #define KSTACK_OFFSET_MAX(x) ((x) & 0b1111111100)
> #endif
>
> +DECLARE_PER_CPU(struct rnd_state, kstack_rnd_state);
> +
> +static __always_inline u32 get_kstack_offset(void)
> +{
> + struct rnd_state *state;
> + u32 rnd;
> +
> + state = &get_cpu_var(kstack_rnd_state);
> + rnd = prandom_u32_state(state);
> + put_cpu_var(kstack_rnd_state);
> +
> + return rnd;
> +}
> [...]
> -static inline void random_kstack_task_init(struct task_struct *tsk)
> +static int random_kstack_init(void)
> {
> - tsk->kstack_offset = 0;
> + prandom_seed_full_state(&kstack_rnd_state);
> + return 0;
> }
> +
> +late_initcall(random_kstack_init);
Doesn't this need to be run for every CPU? (And how does hotplug work
for such things?) And doesn't it need a get_cpu_var?
--
Kees Cook
next prev parent reply other threads:[~2025-12-16 8:27 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-15 16:35 [PATCH v2 0/3] Fix bugs and performance of kstack offset randomisation Ryan Roberts
2025-12-15 16:35 ` [PATCH v2 1/3] randomize_kstack: Maintain kstack_offset per task Ryan Roberts
2025-12-15 16:35 ` [PATCH v2 2/3] prandom: Convert prandom_u32_state() to __always_inline Ryan Roberts
2025-12-15 16:35 ` [PATCH v2 3/3] randomize_kstack: Unify random source across arches Ryan Roberts
2025-12-16 8:27 ` Kees Cook [this message]
2025-12-16 8:30 ` Ard Biesheuvel
2025-12-16 9:16 ` Ryan Roberts
2025-12-16 15:27 ` kernel test robot
2025-12-16 16:31 ` kernel test robot
2026-01-02 12:58 ` Ryan Roberts
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