arm64: mte: add in-kernel MTE helpers

Provide helper functions to manipulate allocation and pointer tags for
kernel addresses.

Low-level helper functions (mte_assign_*, written in assembly) operate tag
values from the [0x0, 0xF] range. High-level helper functions
(mte_get/set_*) use the [0xF0, 0xFF] range to preserve compatibility with
normal kernel pointers that have 0xFF in their top byte.

MTE_GRANULE_SIZE and related definitions are moved to mte-def.h header
that doesn't have any dependencies and is safe to include into any
low-level header.

Link: https://lkml.kernel.org/r/c3[e-mail]
Signed-off-by: Vincenzo Frascino <[e-mail]>
Co-developed-by: Andrey Konovalov <[e-mail]>
Signed-off-by: Andrey Konovalov <[e-mail]>
Reviewed-by: Catalin Marinas <[e-mail]>
Tested-by: Vincenzo Frascino <[e-mail]>
Cc: Alexander Potapenko <[e-mail]>
Cc: Andrey Ryabinin <[e-mail]>
Cc: Branislav Rankov <[e-mail]>
Cc: Dmitry Vyukov <[e-mail]>
Cc: Evgenii Stepanov <[e-mail]>
Cc: Kevin Brodsky <[e-mail]>
Cc: Marco Elver <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Cc: Will Deacon <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/arm64/include/asm/esr.h

···
 #define ESR_ELx_FSC_TYPE	(0x3C)
 #define ESR_ELx_FSC_LEVEL	(0x03)
 #define ESR_ELx_FSC_EXTABT	(0x10)
+#define ESR_ELx_FSC_MTE		(0x11)
 #define ESR_ELx_FSC_SERROR	(0x11)
 #define ESR_ELx_FSC_ACCESS	(0x08)
 #define ESR_ELx_FSC_FAULT	(0x04)

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

···
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020 ARM Ltd.
+ */
+#ifndef __ASM_MTE_DEF_H
+#define __ASM_MTE_DEF_H
+
+#define MTE_GRANULE_SIZE	UL(16)
+#define MTE_GRANULE_MASK	(~(MTE_GRANULE_SIZE - 1))
+#define MTE_TAG_SHIFT		56
+#define MTE_TAG_SIZE		4
+#define MTE_TAG_MASK		GENMASK((MTE_TAG_SHIFT + (MTE_TAG_SIZE - 1)), MTE_TAG_SHIFT)
+#define MTE_TAG_MAX		(MTE_TAG_MASK >> MTE_TAG_SHIFT)
+
+#endif /* __ASM_MTE_DEF_H  */

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

···
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020 ARM Ltd.
+ */
+#ifndef __ASM_MTE_KASAN_H
+#define __ASM_MTE_KASAN_H
+
+#include <asm/mte-def.h>
+
+#ifndef __ASSEMBLY__
+
+#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
+
+static inline u8 mte_get_ptr_tag(void *ptr)
+{
+	/* Note: The format of KASAN tags is 0xF<x> */
+	u8 tag = 0xF0 | (u8)(((u64)(ptr)) >> MTE_TAG_SHIFT);
+
+	return tag;
+}
+
+u8 mte_get_mem_tag(void *addr);
+u8 mte_get_random_tag(void);
+void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag);
+
+#else /* CONFIG_ARM64_MTE */
+
+static inline u8 mte_get_ptr_tag(void *ptr)
+{
+	return 0xFF;
+}
+
+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)
+{
+	return addr;
+}
+
+#endif /* CONFIG_ARM64_MTE */
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* __ASM_MTE_KASAN_H  */

arch/arm64/include/asm/mte.h

···
 #ifndef __ASM_MTE_H
 #define __ASM_MTE_H
 
-#define MTE_GRANULE_SIZE	UL(16)
-#define MTE_GRANULE_MASK	(~(MTE_GRANULE_SIZE - 1))
-#define MTE_TAG_SHIFT		56
-#define MTE_TAG_SIZE		4
+#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>
 #include <linux/page-flags.h>
+#include <linux/types.h>
 
 #include <asm/pgtable-types.h>
 
···
 int mte_ptrace_copy_tags(struct task_struct *child, long request,
 			 unsigned long addr, unsigned long data);
 
-#else
+void mte_assign_mem_tag_range(void *addr, size_t size);
+
+#else /* CONFIG_ARM64_MTE */
 
 /* unused if !CONFIG_ARM64_MTE, silence the compiler */
 #define PG_mte_tagged	0
···
 	return -EIO;
 }
 
-#endif
+static inline void mte_assign_mem_tag_range(void *addr, size_t size)
+{
+}
+
+#endif /* CONFIG_ARM64_MTE */
 
 #endif /* __ASSEMBLY__ */
 #endif /* __ASM_MTE_H  */

arch/arm64/kernel/mte.c

···
 #include <linux/swap.h>
 #include <linux/swapops.h>
 #include <linux/thread_info.h>
+#include <linux/types.h>
 #include <linux/uio.h>
 
+#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>
 
···
 		return addr1 != addr2;
 
 	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;
 }
 
 static void update_sctlr_el1_tcf0(u64 tcf0)

arch/arm64/lib/mte.S

···
 
 	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)