[PATCH v2 3/9] kasan: sw_tags: Support outline stack tag generation

Samuel Holland
2024-10-22T02:05:59Z

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@sifive.com>
---

Changes in v2:
- Split the generic and RISC-V parts of stack tag generation control
to avoid breaking bisectability

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 f438a6cdc964..72da5ddcceaa 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 220b5d4c6876..32435d33583a 100644
--- a/mm/kasan/sw_tags.c
+++ b/mm/kasan/sw_tags.c
@@ -70,6 +70,15 @@ 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)
{
--
2.45.1