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Subject[PATCH v6 05/18] khwasan: initialize shadow to 0xff
Date
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@google.com>
---
arch/arm64/mm/kasan_init.c | 16 ++++++++++++++--
include/linux/kasan.h | 8 ++++++++
mm/kasan/common.c | 3 ++-
3 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
index 12145874c02b..7a31e8ccbad2 100644
--- a/arch/arm64/mm/kasan_init.c
+++ b/arch/arm64/mm/kasan_init.c
@@ -44,6 +44,15 @@ static phys_addr_t __init kasan_alloc_zeroed_page(int node)
return __pa(p);
}

+static phys_addr_t __init kasan_alloc_raw_page(int node)
+{
+ void *p = memblock_virt_alloc_try_nid_raw(PAGE_SIZE, PAGE_SIZE,
+ __pa(MAX_DMA_ADDRESS),
+ MEMBLOCK_ALLOC_ACCESSIBLE,
+ node);
+ return __pa(p);
+}
+
static pte_t *__init kasan_pte_offset(pmd_t *pmdp, unsigned long addr, int node,
bool early)
{
@@ -89,7 +98,9 @@ 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);
+ : kasan_alloc_raw_page(node);
+ if (!early)
+ memset(__va(page_phys), KASAN_SHADOW_INIT, PAGE_SIZE);
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 +150,7 @@ 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));
+
kasan_pgd_populate(KASAN_SHADOW_START, KASAN_SHADOW_END, NUMA_NO_NODE,
true);
}
@@ -235,7 +247,7 @@ 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 beb56a26fe9b..1c31bb089154 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -150,6 +150,8 @@ static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }

#ifdef CONFIG_KASAN_GENERIC

+#define KASAN_SHADOW_INIT 0
+
void kasan_cache_shrink(struct kmem_cache *cache);
void kasan_cache_shutdown(struct kmem_cache *cache);

@@ -160,4 +162,10 @@ static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}

#endif /* CONFIG_KASAN_GENERIC */

+#ifdef CONFIG_KASAN_HW
+
+#define KASAN_SHADOW_INIT 0xFF
+
+#endif /* CONFIG_KASAN_HW */
+
#endif /* LINUX_KASAN_H */
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 154010ba6c1f..bed8e13c6e1d 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -474,11 +474,12 @@ int kasan_module_alloc(void *addr, size_t size)

ret = __vmalloc_node_range(shadow_size, 1, shadow_start,
shadow_start + shadow_size,
- GFP_KERNEL | __GFP_ZERO,
+ GFP_KERNEL,
PAGE_KERNEL, VM_NO_GUARD, NUMA_NO_NODE,
__builtin_return_address(0));

if (ret) {
+ __memset(ret, KASAN_SHADOW_INIT, shadow_size);
find_vm_area(addr)->flags |= VM_KASAN;
kmemleak_ignore(ret);
return 0;
--
2.19.0.rc0.228.g281dcd1b4d0-goog
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