[PATCH 20/35] arm64: mte: Add in-kernel MTE helpers

[Andrey Konovalov <andreyknvl@google.com>]

From: Vincenzo Frascino <vincenzo.frascino@arm.com>

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 definition is moved to mte_asm.h header that doesn't
have any dependencies and is safe to include into any low-level header.

Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Co-developed-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 arch/arm64/include/asm/esr.h     |  1 +
 arch/arm64/include/asm/mte.h     | 46 +++++++++++++++++++++++++++++---
 arch/arm64/include/asm/mte_asm.h | 10 +++++++
 arch/arm64/kernel/mte.c          | 43 +++++++++++++++++++++++++++++
 arch/arm64/lib/mte.S             | 41 ++++++++++++++++++++++++++++
 5 files changed, 138 insertions(+), 3 deletions(-)
 create mode 100644 arch/arm64/include/asm/mte_asm.h

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index 035003acfa87..bc0dc66a6a27 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -103,6 +103,7 @@
 #define ESR_ELx_FSC		(0x3F)
 #define ESR_ELx_FSC_TYPE	(0x3C)
 #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)
diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index 1c99fcadb58c..733be1cb5c95 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -5,14 +5,19 @@
 #ifndef __ASM_MTE_H
 #define __ASM_MTE_H
 
-#define MTE_GRANULE_SIZE	UL(16)
+#include <asm/mte_asm.h>
+
 #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)
 
 #ifndef __ASSEMBLY__
 
+#include <linux/bitfield.h>
 #include <linux/page-flags.h>
+#include <linux/types.h>
 
 #include <asm/pgtable-types.h>
 
@@ -45,7 +50,16 @@ long get_mte_ctrl(struct task_struct *task);
 int mte_ptrace_copy_tags(struct task_struct *child, long request,
 			 unsigned long addr, unsigned long data);
 
-#else
+void *mte_assign_valid_ptr_tag(void *ptr);
+void *mte_assign_random_ptr_tag(void *ptr);
+void mte_assign_mem_tag_range(void *addr, size_t size);
+
+#define mte_get_ptr_tag(ptr)	((u8)(((u64)(ptr)) >> MTE_TAG_SHIFT))
+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 */
 
 /* unused if !CONFIG_ARM64_MTE, silence the compiler */
 #define PG_mte_tagged	0
@@ -80,7 +94,33 @@ static inline int mte_ptrace_copy_tags(struct task_struct *child,
 	return -EIO;
 }
 
-#endif
+static inline void *mte_assign_valid_ptr_tag(void *ptr)
+{
+	return ptr;
+}
+static inline void *mte_assign_random_ptr_tag(void *ptr)
+{
+	return ptr;
+}
+static inline void mte_assign_mem_tag_range(void *addr, size_t size)
+{
+}
+
+#define mte_get_ptr_tag(ptr)	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_H  */
diff --git a/arch/arm64/include/asm/mte_asm.h b/arch/arm64/include/asm/mte_asm.h
new file mode 100644
index 000000000000..aa532c1851e1
--- /dev/null
+++ b/arch/arm64/include/asm/mte_asm.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020 ARM Ltd.
+ */
+#ifndef __ASM_MTE_ASM_H
+#define __ASM_MTE_ASM_H
+
+#define MTE_GRANULE_SIZE	UL(16)
+
+#endif /* __ASM_MTE_ASM_H  */
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index eb39504e390a..e2d708b4583d 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -13,8 +13,10 @@
 #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/ptrace.h>
@@ -72,6 +74,47 @@ int memcmp_pages(struct page *page1, struct page *page2)
 	return ret;
 }
 
+u8 mte_get_mem_tag(void *addr)
+{
+	if (system_supports_mte())
+		addr = mte_assign_valid_ptr_tag(addr);
+
+	return 0xF0 | mte_get_ptr_tag(addr);
+}
+
+u8 mte_get_random_tag(void)
+{
+	u8 tag = 0xF;
+
+	if (system_supports_mte())
+		tag = mte_get_ptr_tag(mte_assign_random_ptr_tag(NULL));
+
+	return 0xF0 | tag;
+}
+
+void * __must_check mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
+{
+	void *ptr = addr;
+
+	if ((!system_supports_mte()) || (size == 0))
+		return addr;
+
+	tag = 0xF0 | (tag & 0xF);
+	ptr = (void *)__tag_set(ptr, tag);
+	size = ALIGN(size, MTE_GRANULE_SIZE);
+
+	mte_assign_mem_tag_range(ptr, size);
+
+	/*
+	 * mte_assign_mem_tag_range() can be invoked in a multi-threaded
+	 * context, ensure that tags are written in memory before the
+	 * reference is used.
+	 */
+	smp_wmb();
+
+	return ptr;
+}
+
 static void update_sctlr_el1_tcf0(u64 tcf0)
 {
 	/* ISB required for the kernel uaccess routines */
diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S
index 03ca6d8b8670..8c743540e32c 100644
--- a/arch/arm64/lib/mte.S
+++ b/arch/arm64/lib/mte.S
@@ -149,3 +149,44 @@ SYM_FUNC_START(mte_restore_page_tags)
 
 	ret
 SYM_FUNC_END(mte_restore_page_tags)
+
+/*
+ * Assign pointer tag based on the allocation tag
+ *   x0 - source pointer
+ * Returns:
+ *   x0 - pointer with the correct tag to access memory
+ */
+SYM_FUNC_START(mte_assign_valid_ptr_tag)
+	ldg	x0, [x0]
+	ret
+SYM_FUNC_END(mte_assign_valid_ptr_tag)
+
+/*
+ * Assign random pointer tag
+ *   x0 - source pointer
+ * Returns:
+ *   x0 - pointer with a random tag
+ */
+SYM_FUNC_START(mte_assign_random_ptr_tag)
+	irg	x0, x0
+	ret
+SYM_FUNC_END(mte_assign_random_ptr_tag)
+
+/*
+ * Assign allocation tags for a region of memory based on the pointer tag
+ *   x0 - source pointer
+ *   x1 - size
+ *
+ * Note: size is expected to be MTE_GRANULE_SIZE aligned
+ */
+SYM_FUNC_START(mte_assign_mem_tag_range)
+	/* if (src == NULL) return; */
+	cbz	x0, 2f
+	/* if (size == 0) return; */
+	cbz	x1, 2f
+1:	stg	x0, [x0]
+	add	x0, x0, #MTE_GRANULE_SIZE
+	sub	x1, x1, #MTE_GRANULE_SIZE
+	cbnz	x1, 1b
+2:	ret
+SYM_FUNC_END(mte_assign_mem_tag_range)
-- 
2.28.0.220.ged08abb693-goog