[RFC PATCH 7/7] kasan: sw_tags: Support runtime stack tagging control for RISC-V

[Samuel Holland]

This allows the kernel to boot on systems without pointer masking
support when stack tagging is enabled.

Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx>
---

 mm/kasan/kasan.h       | 2 ++
 mm/kasan/sw_tags.c     | 9 +++++++++
 scripts/Makefile.kasan | 5 +++++
 3 files changed, 16 insertions(+)

diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
index fb2b9ac0659a..01e945cb111d 100644
--- a/mm/kasan/kasan.h
+++ b/mm/kasan/kasan.h
@@ -630,6 +630,8 @@ 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)
 {
diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index 390658a2d5b7..f64c1aca3e97 100644
--- a/scripts/Makefile.kasan
+++ b/scripts/Makefile.kasan
@@ -73,6 +73,11 @@ ifeq ($(call clang-min-version, 150000)$(call gcc-min-version, 130000),y)
 CFLAGS_KASAN += $(call cc-param,hwasan-kernel-mem-intrinsic-prefix=1)
 endif
 
+# RISC-V requires dynamically determining if stack tagging can be enabled.
+ifdef CONFIG_RISCV
+CFLAGS_KASAN += $(call cc-param,hwasan-generate-tags-with-calls=1)
+endif
+
 endif # CONFIG_KASAN_SW_TAGS
 
 export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE
-- 
2.45.1