[patch 02/18] randomize_kstack: Provide add_random_kstack_offset_irqsoff()
From: Thomas Gleixner <tglx@kernel.org>
Date: 2026-07-07 19:06:05
Also in:
linux-alpha, linux-arch, linux-doc, linux-m68k, linux-mips, linux-riscv, linux-s390, linux-sh, linux-um, lkml, loongarch, sparclinux
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> Cc: Kees Cook <kees@kernel.org> --- include/linux/randomize_kstack.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
--- a/include/linux/randomize_kstack.h
+++ b/include/linux/randomize_kstack.h@@ -77,8 +77,27 @@ static __always_inline u32 get_kstack_of } \ } 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