[RFC PATCH v2 05/15] khwasan: initialize shadow to 0xff

[Andrey Konovalov <andreyknvl@xxxxxxxxxx>]

A KHWASAN shadow memory cell contains a memory tag, that corresponds to
the tag in the top byte of the pointer, that points to that memory. The
native top byte value of kernel pointers is 0xff, so with KHWASAN we
need to initialize shadow memory to 0xff. This commit does that.

Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
 arch/arm64/mm/kasan_init.c | 11 ++++++++++-
 include/linux/kasan.h      |  8 ++++++++
 mm/kasan/common.c          |  7 +++++++
 3 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index dabfc1ecda3d..d4bceba60010 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -90,6 +90,10 @@ static void __init kasan_pte_populate(pmd_t *pmdp, unsigned long addr,
 	do {
 		phys_addr_t page_phys = early ? __pa_symbol(kasan_zero_page)
 					      : kasan_alloc_zeroed_page(node);
+#if KASAN_SHADOW_INIT != 0
+		if (!early)
+			memset(__va(page_phys), KASAN_SHADOW_INIT, PAGE_SIZE);
+#endif
 		next = addr + PAGE_SIZE;
 		set_pte(ptep, pfn_pte(__phys_to_pfn(page_phys), PAGE_KERNEL));
 	} while (ptep++, addr = next, addr != end && pte_none(READ_ONCE(*ptep)));
@@ -139,6 +143,11 @@ asmlinkage void __init kasan_early_init(void)
 		KASAN_SHADOW_END - (1UL << (64 - KASAN_SHADOW_SCALE_SHIFT)));
 	BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_START, PGDIR_SIZE));
 	BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE));
+
+#if KASAN_SHADOW_INIT != 0
+	memset(kasan_zero_page, KASAN_SHADOW_INIT, PAGE_SIZE);
+#endif
+
 	kasan_pgd_populate(KASAN_SHADOW_START, KASAN_SHADOW_END, NUMA_NO_NODE,
 			   true);
 }
@@ -235,7 +244,7 @@ void __init kasan_init(void)
 		set_pte(&kasan_zero_pte[i],
 			pfn_pte(sym_to_pfn(kasan_zero_page), PAGE_KERNEL_RO));
 
-	memset(kasan_zero_page, 0, PAGE_SIZE);
+	memset(kasan_zero_page, KASAN_SHADOW_INIT, PAGE_SIZE);
 	cpu_replace_ttbr1(lm_alias(swapper_pg_dir));
 
 	/* At this point kasan is fully initialized. Enable error messages */
diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 3c45e273a936..700734dff218 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -139,6 +139,8 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
 
 #ifdef CONFIG_KASAN_CLASSIC
 
+#define KASAN_SHADOW_INIT 0
+
 void kasan_cache_shrink(struct kmem_cache *cache);
 void kasan_cache_shutdown(struct kmem_cache *cache);
 
@@ -149,4 +151,10 @@ static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
 
 #endif /* CONFIG_KASAN_CLASSIC */
 
+#ifdef CONFIG_KASAN_TAGS
+
+#define KASAN_SHADOW_INIT 0xFF
+
+#endif /* CONFIG_KASAN_TAGS */
+
 #endif /* LINUX_KASAN_H */
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 08f6c8cb9f84..f4ccb9425655 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -253,6 +253,9 @@ int kasan_module_alloc(void *addr, size_t size)
 			__builtin_return_address(0));
 
 	if (ret) {
+#if KASAN_SHADOW_INIT != 0
+		__memset(ret, KASAN_SHADOW_INIT, shadow_size);
+#endif
 		find_vm_area(addr)->flags |= VM_KASAN;
 		kmemleak_ignore(ret);
 		return 0;
@@ -297,6 +300,10 @@ static int __meminit kasan_mem_notifier(struct notifier_block *nb,
 		if (!ret)
 			return NOTIFY_BAD;
 
+#if KASAN_SHADOW_INIT != 0
+		__memset(ret, KASAN_SHADOW_INIT, shadow_end - shadow_start);
+#endif
+
 		kmemleak_ignore(ret);
 		return NOTIFY_OK;
 	}
-- 
2.17.0.rc0.231.g781580f067-goog