diff options
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/randomize_kstack.h | 52 | ||||
| -rw-r--r-- | include/linux/sched.h | 4 |
2 files changed, 17 insertions, 39 deletions
diff --git a/include/linux/randomize_kstack.h b/include/linux/randomize_kstack.h index 5d3916ca747c..024fc20e7762 100644 --- a/include/linux/randomize_kstack.h +++ b/include/linux/randomize_kstack.h @@ -6,6 +6,7 @@ #include <linux/kernel.h> #include <linux/jump_label.h> #include <linux/percpu-defs.h> +#include <linux/prandom.h> DECLARE_STATIC_KEY_MAYBE(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, randomize_kstack_offset); @@ -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; +} + /** - * add_random_kstack_offset - Increase stack utilization by previously - * chosen random offset + * add_random_kstack_offset - 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. Preemption may be enabled. For testing the resulting @@ -56,47 +70,15 @@ DECLARE_STATIC_KEY_MAYBE(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, #define add_random_kstack_offset() do { \ if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \ &randomize_kstack_offset)) { \ - u32 offset = current->kstack_offset; \ + u32 offset = get_kstack_offset(); \ u8 *ptr = __kstack_alloca(KSTACK_OFFSET_MAX(offset)); \ /* Keep allocation even after "ptr" loses scope. */ \ asm volatile("" :: "r"(ptr) : "memory"); \ } \ } while (0) -/** - * choose_random_kstack_offset - Choose the random offset for the next - * add_random_kstack_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 - * kernel mode?" tends to be more difficult to predict than "how long - * will we be in user mode?" - * - Reduce the lifetime of the new offset sitting in memory during - * kernel mode execution. Exposure of "thread-local" memory content - * (e.g. current, percpu, etc) tends to be easier than arbitrary - * location memory exposure. - */ -#define choose_random_kstack_offset(rand) do { \ - if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \ - &randomize_kstack_offset)) { \ - u32 offset = current->kstack_offset; \ - offset = ror32(offset, 5) ^ (rand); \ - 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 diff --git a/include/linux/sched.h b/include/linux/sched.h index 8358e430dd7f..a7b4a980eb2f 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1592,10 +1592,6 @@ struct task_struct { unsigned long prev_lowest_stack; #endif -#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET - u32 kstack_offset; -#endif - #ifdef CONFIG_X86_MCE void __user *mce_vaddr; __u64 mce_kflags; |