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authorSami Tolvanen <samitolvanen@google.com>2020-12-01 02:34:41 +0300
committerWill Deacon <will@kernel.org>2020-12-01 13:30:28 +0300
commita2abe7cbd8fe2db5ff386c968e2273d9dc6c468d (patch)
tree7b00fd0f4e632398c41a56cf0ee4d001922c928f /include/linux/scs.h
parentf8394f232b1eab649ce2df5c5f15b0e528c92091 (diff)
downloadlinux-a2abe7cbd8fe2db5ff386c968e2273d9dc6c468d.tar.xz
scs: switch to vmapped shadow stacks
The kernel currently uses kmem_cache to allocate shadow call stacks, which means an overflows may not be immediately detected and can potentially result in another task's shadow stack to be overwritten. This change switches SCS to use virtually mapped shadow stacks for tasks, which increases shadow stack size to a full page and provides more robust overflow detection, similarly to VMAP_STACK. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Acked-by: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20201130233442.2562064-2-samitolvanen@google.com Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'include/linux/scs.h')
-rw-r--r--include/linux/scs.h12
1 files changed, 6 insertions, 6 deletions
diff --git a/include/linux/scs.h b/include/linux/scs.h
index 6dec390cf154..2a506c2a16f4 100644
--- a/include/linux/scs.h
+++ b/include/linux/scs.h
@@ -15,12 +15,8 @@
#ifdef CONFIG_SHADOW_CALL_STACK
-/*
- * In testing, 1 KiB shadow stack size (i.e. 128 stack frames on a 64-bit
- * architecture) provided ~40% safety margin on stack usage while keeping
- * memory allocation overhead reasonable.
- */
-#define SCS_SIZE SZ_1K
+#define SCS_ORDER 0
+#define SCS_SIZE (PAGE_SIZE << SCS_ORDER)
#define GFP_SCS (GFP_KERNEL | __GFP_ZERO)
/* An illegal pointer value to mark the end of the shadow stack. */
@@ -33,6 +29,8 @@
#define task_scs(tsk) (task_thread_info(tsk)->scs_base)
#define task_scs_sp(tsk) (task_thread_info(tsk)->scs_sp)
+void *scs_alloc(int node);
+void scs_free(void *s);
void scs_init(void);
int scs_prepare(struct task_struct *tsk, int node);
void scs_release(struct task_struct *tsk);
@@ -61,6 +59,8 @@ static inline bool task_scs_end_corrupted(struct task_struct *tsk)
#else /* CONFIG_SHADOW_CALL_STACK */
+static inline void *scs_alloc(int node) { return NULL; }
+static inline void scs_free(void *s) {}
static inline void scs_init(void) {}
static inline void scs_task_reset(struct task_struct *tsk) {}
static inline int scs_prepare(struct task_struct *tsk, int node) { return 0; }