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

From: Samuel Holland <samuel.holland@sifive.com>
To: Palmer Dabbelt <palmer@dabbelt.com>,
	linux-riscv@lists.infradead.org,
	Andrey Ryabinin <ryabinin.a.a@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Andrey Konovalov <andreyknvl@gmail.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	kasan-dev@googlegroups.com
Cc: llvm@lists.linux.dev, Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Alexandre Ghiti <alexghiti@rivosinc.com>,
	Will Deacon <will@kernel.org>,
	Evgenii Stepanov <eugenis@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-arm-kernel@lists.infradead.org,
	Samuel Holland <samuel.holland@sifive.com>
Subject: [PATCH v2 3/9] kasan: sw_tags: Support outline stack tag generation
Date: Mon, 21 Oct 2024 18:57:11 -0700	[thread overview]
Message-ID: <20241022015913.3524425-4-samuel.holland@sifive.com> (raw)
In-Reply-To: <20241022015913.3524425-1-samuel.holland@sifive.com>

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

