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randomize_kstack: Provide add_random_kstack_offset_irqsoff()

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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 <tglx@kernel.org>
Reviewed-by: Radu Rendec <radu@rendec.net>
Reviewed-by: Kees Cook <kees@kernel.org>
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
Link: https://patch.msgid.link/20260707190253.768842729@kernel.org
This commit is contained in:
Thomas Gleixner
2026-07-12 12:38:00 +02:00
parent 89d163dd9d
commit 0b9a305753
1 changed files with 19 additions and 0 deletions
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include/linux/randomize_kstack.h
+19
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@@ -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