stackleak: Rename STACKLEAK to KSTACK_ERASE

In preparation for adding Clang sanitizer coverage stack depth tracking
that can support stack depth callbacks:

- Add the new top-level CONFIG_KSTACK_ERASE option which will be
  implemented either with the stackleak GCC plugin, or with the Clang
  stack depth callback support.
- Rename CONFIG_GCC_PLUGIN_STACKLEAK as needed to CONFIG_KSTACK_ERASE,
  but keep it for anything specific to the GCC plugin itself.
- Rename all exposed "STACKLEAK" names and files to "KSTACK_ERASE" (named
  for what it does rather than what it protects against), but leave as
  many of the internals alone as possible to avoid even more churn.

While here, also split "prev_lowest_stack" into CONFIG_KSTACK_ERASE_METRICS,
since that's the only place it is referenced from.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250717232519.2984886-1-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>

2 files changed, 12 insertions, 10 deletions

diff --git a/include/linux/stackleak.h b/include/linux/kstack_erase.h
index 3be2cb564710..4e432eefa4d0 100644
--- a/include/linux/stackleak.h
+++ b/include/linux/kstack_erase.h
@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _LINUX_STACKLEAK_H
-#define _LINUX_STACKLEAK_H
+#ifndef _LINUX_KSTACK_ERASE_H
+#define _LINUX_KSTACK_ERASE_H
 
 #include <linux/sched.h>
 #include <linux/sched/task_stack.h>
@@ -9,10 +9,10 @@
  * Check that the poison value points to the unused hole in the
  * virtual memory map for your platform.
  */
-#define STACKLEAK_POISON -0xBEEF
-#define STACKLEAK_SEARCH_DEPTH 128
+#define KSTACK_ERASE_POISON -0xBEEF
+#define KSTACK_ERASE_SEARCH_DEPTH 128
 
-#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+#ifdef CONFIG_KSTACK_ERASE
 #include <asm/stacktrace.h>
 #include <linux/linkage.h>
 
@@ -50,7 +50,7 @@ stackleak_task_high_bound(const struct task_struct *tsk)
 static __always_inline unsigned long
 stackleak_find_top_of_poison(const unsigned long low, const unsigned long high)
 {
-	const unsigned int depth = STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
+	const unsigned int depth = KSTACK_ERASE_SEARCH_DEPTH / sizeof(unsigned long);
 	unsigned int poison_count = 0;
 	unsigned long poison_high = high;
 	unsigned long sp = high;
@@ -58,7 +58,7 @@ stackleak_find_top_of_poison(const unsigned long low, const unsigned long high)
 	while (sp > low && poison_count < depth) {
 		sp -= sizeof(unsigned long);
 
-		if (*(unsigned long *)sp == STACKLEAK_POISON) {
+		if (*(unsigned long *)sp == KSTACK_ERASE_POISON) {
 			poison_count++;
 		} else {
 			poison_count = 0;
@@ -72,7 +72,7 @@ stackleak_find_top_of_poison(const unsigned long low, const unsigned long high)
 static inline void stackleak_task_init(struct task_struct *t)
 {
 	t->lowest_stack = stackleak_task_low_bound(t);
-# ifdef CONFIG_STACKLEAK_METRICS
+# ifdef CONFIG_KSTACK_ERASE_METRICS
 	t->prev_lowest_stack = t->lowest_stack;
 # endif
 }
@@ -82,7 +82,7 @@ asmlinkage void noinstr stackleak_erase_on_task_stack(void);
 asmlinkage void noinstr stackleak_erase_off_task_stack(void);
 void __no_caller_saved_registers noinstr stackleak_track_stack(void);
 
-#else /* !CONFIG_GCC_PLUGIN_STACKLEAK */
+#else /* !CONFIG_KSTACK_ERASE */
 static inline void stackleak_task_init(struct task_struct *t) { }
 #endif
 
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4f78a64beb52..b7d2f2fd4cd4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1607,8 +1607,10 @@ struct task_struct {
 	/* Used by BPF for per-TASK xdp storage */
 	struct bpf_net_context		*bpf_net_context;
 
-#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+#ifdef CONFIG_KSTACK_ERASE
 	unsigned long			lowest_stack;
+#endif
+#ifdef CONFIG_KSTACK_ERASE_METRICS
 	unsigned long			prev_lowest_stack;
 #endif