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authorMark Rutland <mark.rutland@arm.com>2022-04-27 20:31:20 +0300
committerKees Cook <keescook@chromium.org>2022-05-08 11:33:08 +0300
commit1723d39d2fe49b8a75939060c95e7e908b463793 (patch)
tree952b398c8b3bac669c17fe46228d5e589098d682 /kernel/stackleak.c
parent9ec79840d6afaf472294588a6bbe145bcdffa28b (diff)
downloadlinux-1723d39d2fe49b8a75939060c95e7e908b463793.tar.xz
stackleak: clarify variable names
The logic within __stackleak_erase() can be a little hard to follow, as `boundary` switches from being the low bound to the high bound mid way through the function, and `kstack_ptr` is used to represent the start of the region to erase while `boundary` represents the end of the region to erase. Make this a little clearer by consistently using clearer variable names. The `boundary` variable is removed, the bounds of the region to erase are described by `erase_low` and `erase_high`, and bounds of the task stack are described by `task_stack_low` and `task_stack_high`. As the same time, remove the comment above the variables, since it is unclear whether it's intended as rationale, a complaint, or a TODO, and is more confusing than helpful. There should be no functional change as a result of this patch. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Popov <alex.popov@linux.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Kees Cook <keescook@chromium.org> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20220427173128.2603085-6-mark.rutland@arm.com
Diffstat (limited to 'kernel/stackleak.c')
-rw-r--r--kernel/stackleak.c30
1 files changed, 14 insertions, 16 deletions
diff --git a/kernel/stackleak.c b/kernel/stackleak.c
index 24b7cf01b297..d5f684dc0a2d 100644
--- a/kernel/stackleak.c
+++ b/kernel/stackleak.c
@@ -73,40 +73,38 @@ late_initcall(stackleak_sysctls_init);
static __always_inline void __stackleak_erase(void)
{
const unsigned long task_stack_low = stackleak_task_low_bound(current);
-
- /* It would be nice not to have 'kstack_ptr' and 'boundary' on stack */
- unsigned long kstack_ptr = current->lowest_stack;
- unsigned long boundary = task_stack_low;
+ unsigned long erase_low = current->lowest_stack;
+ unsigned long erase_high;
unsigned int poison_count = 0;
const unsigned int depth = STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
/* Search for the poison value in the kernel stack */
- while (kstack_ptr > boundary && poison_count <= depth) {
- if (*(unsigned long *)kstack_ptr == STACKLEAK_POISON)
+ while (erase_low > task_stack_low && poison_count <= depth) {
+ if (*(unsigned long *)erase_low == STACKLEAK_POISON)
poison_count++;
else
poison_count = 0;
- kstack_ptr -= sizeof(unsigned long);
+ erase_low -= sizeof(unsigned long);
}
#ifdef CONFIG_STACKLEAK_METRICS
- current->prev_lowest_stack = kstack_ptr;
+ current->prev_lowest_stack = erase_low;
#endif
/*
- * Now write the poison value to the kernel stack. Start from
- * 'kstack_ptr' and move up till the new 'boundary'. We assume that
- * the stack pointer doesn't change when we write poison.
+ * Now write the poison value to the kernel stack between 'erase_low'
+ * and 'erase_high'. We assume that the stack pointer doesn't change
+ * when we write poison.
*/
if (on_thread_stack())
- boundary = current_stack_pointer;
+ erase_high = current_stack_pointer;
else
- boundary = current_top_of_stack();
+ erase_high = current_top_of_stack();
- while (kstack_ptr < boundary) {
- *(unsigned long *)kstack_ptr = STACKLEAK_POISON;
- kstack_ptr += sizeof(unsigned long);
+ while (erase_low < erase_high) {
+ *(unsigned long *)erase_low = STACKLEAK_POISON;
+ erase_low += sizeof(unsigned long);
}
/* Reset the 'lowest_stack' value for the next syscall */