arm64: kasan: simplify and inline MTE functions

This change provides a simpler implementation of mte_get_mem_tag(),
mte_get_random_tag(), and mte_set_mem_tag_range().

Simplifications include removing system_supports_mte() checks as these
functions are onlye called from KASAN runtime that had already checked
system_supports_mte().  Besides that, size and address alignment checks
are removed from mte_set_mem_tag_range(), as KASAN now does those.

This change also moves these functions into the asm/mte-kasan.h header and
implements mte_set_mem_tag_range() via inline assembly to avoid
unnecessary functions calls.

[vincenzo.frascino@arm.com: fix warning in mte_get_random_tag()]
  Link: https://lkml.kernel.org/r/20210211152208.23811-1-vincenzo.frascino@arm.com

Link: https://lkml.kernel.org/r/a26121b294fdf76e369cb7a74351d1c03a908930.1612546384.git.andreyknvl@google.com
Co-developed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Marco Elver <elver@google.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/arm64/include/asm/cache.h

@@ -6,7 +6,6 @@
 #define __ASM_CACHE_H
 
 #include <asm/cputype.h>
-#include <asm/mte-kasan.h>
 
 #define CTR_L1IP_SHIFT		14
 #define CTR_L1IP_MASK		3

arch/arm64/include/asm/kasan.h

@@ -6,6 +6,7 @@
 
 #include <linux/linkage.h>
 #include <asm/memory.h>
+#include <asm/mte-kasan.h>
 #include <asm/pgtable-types.h>
 
 #define arch_kasan_set_tag(addr, tag)	__tag_set(addr, tag)

arch/arm64/include/asm/mte-def.h

@@ -11,4 +11,6 @@
 #define MTE_TAG_SIZE		4
 #define MTE_TAG_MASK		GENMASK((MTE_TAG_SHIFT + (MTE_TAG_SIZE - 1)), MTE_TAG_SHIFT)
 
+#define __MTE_PREAMBLE		ARM64_ASM_PREAMBLE ".arch_extension memtag\n"
+
 #endif /* __ASM_MTE_DEF_H  */

arch/arm64/include/asm/mte-kasan.h

@@ -11,12 +11,15 @@
 
 #include <linux/types.h>
 
-/*
- * The functions below are meant to be used only for the
- * KASAN_HW_TAGS interface defined in asm/memory.h.
- */
 #ifdef CONFIG_ARM64_MTE
 
+/*
+ * These functions are meant to be only used from KASAN runtime through
+ * the arch_*() interface defined in asm/memory.h.
+ * These functions don't include system_supports_mte() checks,
+ * as KASAN only calls them when MTE is supported and enabled.
+ */
+
 static inline u8 mte_get_ptr_tag(void *ptr)
 {
 	/* Note: The format of KASAN tags is 0xF<x> */
@@ -25,9 +28,54 @@ static inline u8 mte_get_ptr_tag(void *ptr)
 	return tag;
 }
 
-u8 mte_get_mem_tag(void *addr);
+/* Get allocation tag for the address. */
-u8 mte_get_random_tag(void);
+static inline u8 mte_get_mem_tag(void *addr)
-void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag);
+{
+	asm(__MTE_PREAMBLE "ldg %0, [%0]"
+		: "+r" (addr));
+
+	return mte_get_ptr_tag(addr);
+}
+
+/* Generate a random tag. */
+static inline u8 mte_get_random_tag(void)
+{
+	void *addr;
+
+	asm(__MTE_PREAMBLE "irg %0, %0"
+		: "=r" (addr));
+
+	return mte_get_ptr_tag(addr);
+}
+
+/*
+ * 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.
+ */
+static 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(void);
 void mte_init_tags(u64 max_tag);
@@ -46,13 +94,14 @@ 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)
+
+static inline void mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
 {
-	return addr;
 }
 
 static inline void mte_enable_kernel(void)

arch/arm64/include/asm/mte.h

@@ -8,8 +8,6 @@
 #include <asm/compiler.h>
 #include <asm/mte-def.h>
 
-#define __MTE_PREAMBLE		ARM64_ASM_PREAMBLE ".arch_extension memtag\n"
-
 #ifndef __ASSEMBLY__
 
 #include <linux/bitfield.h>

arch/arm64/kernel/mte.c

@@ -19,7 +19,6 @@
 #include <asm/barrier.h>
 #include <asm/cpufeature.h>
 #include <asm/mte.h>
-#include <asm/mte-kasan.h>
 #include <asm/ptrace.h>
 #include <asm/sysreg.h>
 
@@ -88,51 +87,6 @@ int memcmp_pages(struct page *page1, struct page *page2)
 	return ret;
 }
 
-u8 mte_get_mem_tag(void *addr)
-{
-	if (!system_supports_mte())
-		return 0xFF;
-
-	asm(__MTE_PREAMBLE "ldg %0, [%0]"
-	    : "+r" (addr));
-
-	return mte_get_ptr_tag(addr);
-}
-
-u8 mte_get_random_tag(void)
-{
-	void *addr;
-
-	if (!system_supports_mte())
-		return 0xFF;
-
-	asm(__MTE_PREAMBLE "irg %0, %0"
-	    : "+r" (addr));
-
-	return mte_get_ptr_tag(addr);
-}
-
-void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
-{
-	void *ptr = addr;
-
-	if ((!system_supports_mte()) || (size == 0))
-		return addr;
-
-	/* Make sure that size is MTE granule aligned. */
-	WARN_ON(size & (MTE_GRANULE_SIZE - 1));
-
-	/* Make sure that the address is MTE granule aligned. */
-	WARN_ON((u64)addr & (MTE_GRANULE_SIZE - 1));
-
-	tag = 0xF0 | tag;
-	ptr = (void *)__tag_set(ptr, tag);
-
-	mte_assign_mem_tag_range(ptr, size);
-
-	return ptr;
-}
-
 void mte_init_tags(u64 max_tag)
 {
 	static bool gcr_kernel_excl_initialized;

arch/arm64/lib/mte.S

@@ -149,19 +149,3 @@ SYM_FUNC_START(mte_restore_page_tags)
 
 	ret
 SYM_FUNC_END(mte_restore_page_tags)
-
-/*
- * Assign allocation tags for a region of memory based on the pointer tag
- *   x0 - source pointer
- *   x1 - size
- *
- * Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and
- * size must be non-zero and MTE_GRANULE_SIZE aligned.
- */
-SYM_FUNC_START(mte_assign_mem_tag_range)
-1:	stg	x0, [x0]
-	add	x0, x0, #MTE_GRANULE_SIZE
-	subs	x1, x1, #MTE_GRANULE_SIZE
-	b.gt	1b
-	ret
-SYM_FUNC_END(mte_assign_mem_tag_range)