From 0b9a3057530cc1c3f87ce2ab9d1278164e81990f Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Tue, 7 Jul 2026 21:06:02 +0200 Subject: [PATCH] randomize_kstack: Provide add_random_kstack_offset_irqsoff() add_random_kstack_offset() uses get/put_cpu_var() which is pointless overhead when it is invoked from low level entry code with interrupts disabled. Provide a irqsoff() variant, which avoids that. Signed-off-by: Thomas Gleixner Reviewed-by: Radu Rendec Reviewed-by: Kees Cook Reviewed-by: Mukesh Kumar Chaurasiya (IBM) Link: https://patch.msgid.link/20260707190253.768842729@kernel.org --- include/linux/randomize_kstack.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/include/linux/randomize_kstack.h b/include/linux/randomize_kstack.h index 024fc20e7762..d8b939f50bba 100644 --- a/include/linux/randomize_kstack.h +++ b/include/linux/randomize_kstack.h @@ -77,8 +77,27 @@ static __always_inline u32 get_kstack_offset(void) } \ } while (0) +/** + * add_random_kstack_offset_irqsoff - Increase stack utilization by a random offset. + * + * This should be used in the syscall entry path after user registers have been + * stored to the stack. Interrupts must be still disabled. + */ +#define add_random_kstack_offset_irqsoff() \ +do { \ + lockdep_assert_irqs_disabled(); \ + if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \ + &randomize_kstack_offset)) { \ + u32 offset = prandom_u32_state(raw_cpu_ptr(&kstack_rnd_state)); \ + u8 *ptr = __kstack_alloca(KSTACK_OFFSET_MAX(offset)); \ + /* Keep allocation even after "ptr" loses scope. */ \ + asm volatile("" :: "r"(ptr) : "memory"); \ + } \ +} while (0) + #else /* CONFIG_RANDOMIZE_KSTACK_OFFSET */ #define add_random_kstack_offset() do { } while (0) +#define add_random_kstack_offset_irqsoff() do { } while (0) #endif /* CONFIG_RANDOMIZE_KSTACK_OFFSET */ #endif