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

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Message-ID: <20241022015913.3524425-4-samuel.holland@sifive.com>
Date: Mon, 21 Oct 2024 18:57:11 -0700
From: Samuel Holland <samuel.holland@...ive.com>
To: Palmer Dabbelt <palmer@...belt.com>,
	linux-riscv@...ts.infradead.org,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Alexander Potapenko <glider@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Vincenzo Frascino <vincenzo.frascino@....com>,
	kasan-dev@...glegroups.com
Cc: llvm@...ts.linux.dev,
	Catalin Marinas <catalin.marinas@....com>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	Will Deacon <will@...nel.org>,
	Evgenii Stepanov <eugenis@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arm-kernel@...ts.infradead.org,
	Samuel Holland <samuel.holland@...ive.com>
Subject: [PATCH v2 3/9] kasan: sw_tags: Support outline stack tag generation

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@...ive.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