1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _LINUX_STACKLEAK_H 3 #define _LINUX_STACKLEAK_H 4 5 #include <linux/sched.h> 6 #include <linux/sched/task_stack.h> 7 8 /* 9 * Check that the poison value points to the unused hole in the 10 * virtual memory map for your platform. 11 */ 12 #define STACKLEAK_POISON -0xBEEF 13 #define STACKLEAK_SEARCH_DEPTH 128 14 15 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK 16 #include <asm/stacktrace.h> 17 #include <linux/linkage.h> 18 19 /* 20 * The lowest address on tsk's stack which we can plausibly erase. 21 */ 22 static __always_inline unsigned long 23 stackleak_task_low_bound(const struct task_struct *tsk) 24 { 25 /* 26 * The lowest unsigned long on the task stack contains STACK_END_MAGIC, 27 * which we must not corrupt. 28 */ 29 return (unsigned long)end_of_stack(tsk) + sizeof(unsigned long); 30 } 31 32 /* 33 * The address immediately after the highest address on tsk's stack which we 34 * can plausibly erase. 35 */ 36 static __always_inline unsigned long 37 stackleak_task_high_bound(const struct task_struct *tsk) 38 { 39 /* 40 * The task's pt_regs lives at the top of the task stack and will be 41 * overwritten by exception entry, so there's no need to erase them. 42 */ 43 return (unsigned long)task_pt_regs(tsk); 44 } 45 46 /* 47 * Find the address immediately above the poisoned region of the stack, where 48 * that region falls between 'low' (inclusive) and 'high' (exclusive). 49 */ 50 static __always_inline unsigned long 51 stackleak_find_top_of_poison(const unsigned long low, const unsigned long high) 52 { 53 const unsigned int depth = STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long); 54 unsigned int poison_count = 0; 55 unsigned long poison_high = high; 56 unsigned long sp = high; 57 58 while (sp > low && poison_count < depth) { 59 sp -= sizeof(unsigned long); 60 61 if (*(unsigned long *)sp == STACKLEAK_POISON) { 62 poison_count++; 63 } else { 64 poison_count = 0; 65 poison_high = sp; 66 } 67 } 68 69 return poison_high; 70 } 71 72 static inline void stackleak_task_init(struct task_struct *t) 73 { 74 t->lowest_stack = stackleak_task_low_bound(t); 75 # ifdef CONFIG_STACKLEAK_METRICS 76 t->prev_lowest_stack = t->lowest_stack; 77 # endif 78 } 79 80 asmlinkage void noinstr stackleak_erase(void); 81 asmlinkage void noinstr stackleak_erase_on_task_stack(void); 82 asmlinkage void noinstr stackleak_erase_off_task_stack(void); 83 void __no_caller_saved_registers noinstr stackleak_track_stack(void); 84 85 #else /* !CONFIG_GCC_PLUGIN_STACKLEAK */ 86 static inline void stackleak_task_init(struct task_struct *t) { } 87 #endif 88 89 #endif 90