Re: [PATCH 10/12] arm64: kasan: simplify and inline MTE functions

On Tue, Feb 2, 2021 at 4:42 PM Catalin Marinas [off-list ref] wrote:

On Mon, Feb 01, 2021 at 08:43:34PM +0100, Andrey Konovalov wrote:

quoted

+/*
+ * Assign allocation tags for a region of memory based on the pointer tag.
+ * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and
+ * size must be non-zero and MTE_GRANULE_SIZE aligned.
+ */

OK, so we rely on the caller to sanity-check the range. Fine by me but I
can see (un)poison_range() only doing this for the size. Do we guarantee
that the start address is aligned?

See the previous patch in the series. kasan_poison() checks and warns
on both unaligned addr and size. kasan_unpoison() checks addr and
rounds up size.

quoted

+static __always_inline void mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
+{
+     u64 curr, end;
+
+     if (!size)
+             return;
+
+     curr = (u64)__tag_set(addr, tag);
+     end = curr + size;
+
+     do {
+             /*
+              * 'asm volatile' is required to prevent the compiler to move
+              * the statement outside of the loop.
+              */
+             asm volatile(__MTE_PREAMBLE "stg %0, [%0]"
+                          :
+                          : "r" (curr)
+                          : "memory");
+
+             curr += MTE_GRANULE_SIZE;
+     } while (curr != end);
+}

 void mte_enable_kernel_sync(void);
 void mte_enable_kernel_async(void);

@@ -47,10 +95,12 @@ static inline u8 mte_get_mem_tag(void *addr)
 {
      return 0xFF;
 }
+
 static inline u8 mte_get_random_tag(void)
 {
      return 0xFF;
 }
+
 static inline void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)

This function used to return a pointer and that's what the dummy static
inline does here. However, the new mte_set_mem_tag_range() doesn't
return anything. We should have consistency between the two (the new
static void definition is fine by me).

Right, forgot to update the empty function definition. Will do in v2.

Otherwise the patch looks fine.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Thanks!

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