[PATCH v2 03/14] kasan: sw_tags: Support outline stack tag generation

[Maciej Wieczor-Retman]

From: Samuel Holland <samuel.holland@xxxxxxxxxx>

This allows stack tagging to be disabled at runtime by tagging all
stack objects with the match-all tag. This is necessary on RISC-V,
where a kernel with KASAN_SW_TAGS enabled is expected to boot on
hardware without pointer masking support.

Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx>
Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
---
 mm/kasan/kasan.h   | 2 ++
 mm/kasan/sw_tags.c | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index 129178be5e64..2fb26f74dff9 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -636,6 +636,8 @@ void *__asan_memset(void *addr, int c, ssize_t len);
 void *__asan_memmove(void *dest, const void *src, ssize_t len);
 void *__asan_memcpy(void *dest, const void *src, ssize_t len);
 
+u8 __hwasan_generate_tag(void);
+
 void __hwasan_load1_noabort(void *);
 void __hwasan_store1_noabort(void *);
 void __hwasan_load2_noabort(void *);
diff --git a/mm/kasan/sw_tags.c b/mm/kasan/sw_tags.c
index b9382b5b6a37..94465a8a3640 100644
--- a/mm/kasan/sw_tags.c
+++ b/mm/kasan/sw_tags.c
@@ -71,6 +71,15 @@ u8 kasan_random_tag(void)
 	return (u8)(state % (KASAN_TAG_MAX + 1));
 }
 
+u8 __hwasan_generate_tag(void)
+{
+	if (!kasan_enabled())
+		return KASAN_TAG_KERNEL;
+
+	return kasan_random_tag();
+}
+EXPORT_SYMBOL(__hwasan_generate_tag);
+
 bool kasan_check_range(const void *addr, size_t size, bool write,
 			unsigned long ret_ip)
 {
-- 
2.47.1