Re: [PATCH v2 3/3] randomize_kstack: Unify random source across arches
From: Kees Cook <kees@kernel.org>
Date: 2025-12-16 08:27:39
Also in:
linux-arm-kernel, linux-hardening, linux-riscv, linux-s390, lkml, loongarch
On Mon, Dec 15, 2025 at 04:35:17PM +0000, Ryan Roberts wrote:
quoted hunk ↗ jump to hunk
[...]@@ -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