diff options
Diffstat (limited to 'include/linux/randomize_kstack.h')
| -rw-r--r-- | include/linux/randomize_kstack.h | 26 |
1 files changed, 15 insertions, 11 deletions
diff --git a/include/linux/randomize_kstack.h b/include/linux/randomize_kstack.h index 1d982dbdd0d0..5d3916ca747c 100644 --- a/include/linux/randomize_kstack.h +++ b/include/linux/randomize_kstack.h @@ -9,7 +9,6 @@ DECLARE_STATIC_KEY_MAYBE(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, randomize_kstack_offset); -DECLARE_PER_CPU(u32, kstack_offset); /* * Do not use this anywhere else in the kernel. This is used here because @@ -50,15 +49,14 @@ DECLARE_PER_CPU(u32, kstack_offset); * add_random_kstack_offset - Increase stack utilization by previously * chosen random offset * - * This should be used in the syscall entry path when interrupts and - * preempt are disabled, and after user registers have been stored to - * the stack. For testing the resulting entropy, please see: - * tools/testing/selftests/lkdtm/stack-entropy.sh + * This should be used in the syscall entry path after user registers have been + * stored to the stack. Preemption may be enabled. For testing the resulting + * entropy, please see: tools/testing/selftests/lkdtm/stack-entropy.sh */ #define add_random_kstack_offset() do { \ if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \ &randomize_kstack_offset)) { \ - u32 offset = raw_cpu_read(kstack_offset); \ + u32 offset = current->kstack_offset; \ u8 *ptr = __kstack_alloca(KSTACK_OFFSET_MAX(offset)); \ /* Keep allocation even after "ptr" loses scope. */ \ asm volatile("" :: "r"(ptr) : "memory"); \ @@ -69,9 +67,9 @@ DECLARE_PER_CPU(u32, kstack_offset); * choose_random_kstack_offset - Choose the random offset for the next * add_random_kstack_offset() * - * This should only be used during syscall exit when interrupts and - * preempt are disabled. This position in the syscall flow is done to - * frustrate attacks from userspace attempting to learn the next offset: + * This should only be used during syscall exit. Preemption may be enabled. This + * position in the syscall flow is done to frustrate attacks from userspace + * attempting to learn the next offset: * - Maximize the timing uncertainty visible from userspace: if the * offset is chosen at syscall entry, userspace has much more control * over the timing between choosing offsets. "How long will we be in @@ -85,14 +83,20 @@ DECLARE_PER_CPU(u32, kstack_offset); #define choose_random_kstack_offset(rand) do { \ if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \ &randomize_kstack_offset)) { \ - u32 offset = raw_cpu_read(kstack_offset); \ + u32 offset = current->kstack_offset; \ offset = ror32(offset, 5) ^ (rand); \ - raw_cpu_write(kstack_offset, offset); \ + current->kstack_offset = offset; \ } \ } while (0) + +static inline void random_kstack_task_init(struct task_struct *tsk) +{ + tsk->kstack_offset = 0; +} #else /* CONFIG_RANDOMIZE_KSTACK_OFFSET */ #define add_random_kstack_offset() do { } while (0) #define choose_random_kstack_offset(rand) do { } while (0) +#define random_kstack_task_init(tsk) do { } while (0) #endif /* CONFIG_RANDOMIZE_KSTACK_OFFSET */ #endif |