1 files changed, 258 insertions, 0 deletions
diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
new file mode 100644
index 0000000000..2e98028c19
--- /dev/null
+++ b/arch/arm64/include/asm/mte-kasan.h
@@ -0,0 +1,258 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020 ARM Ltd.
+ */
+#ifndef __ASM_MTE_KASAN_H
+#define __ASM_MTE_KASAN_H
+
+#include <asm/compiler.h>
+#include <asm/cputype.h>
+#include <asm/mte-def.h>
+
+#ifndef __ASSEMBLY__
+
+#include <linux/types.h>
+
+#ifdef CONFIG_KASAN_HW_TAGS
+
+/* Whether the MTE asynchronous mode is enabled. */
+DECLARE_STATIC_KEY_FALSE(mte_async_or_asymm_mode);
+
+static inline bool system_uses_mte_async_or_asymm_mode(void)
+{
+	return static_branch_unlikely(&mte_async_or_asymm_mode);
+}
+
+#else /* CONFIG_KASAN_HW_TAGS */
+
+static inline bool system_uses_mte_async_or_asymm_mode(void)
+{
+	return false;
+}
+
+#endif /* CONFIG_KASAN_HW_TAGS */
+
+#ifdef CONFIG_ARM64_MTE
+
+/*
+ * The Tag Check Flag (TCF) mode for MTE is per EL, hence TCF0
+ * affects EL0 and TCF affects EL1 irrespective of which TTBR is
+ * used.
+ * The kernel accesses TTBR0 usually with LDTR/STTR instructions
+ * when UAO is available, so these would act as EL0 accesses using
+ * TCF0.
+ * However futex.h code uses exclusives which would be executed as
+ * EL1, this can potentially cause a tag check fault even if the
+ * user disables TCF0.
+ *
+ * To address the problem we set the PSTATE.TCO bit in uaccess_enable()
+ * and reset it in uaccess_disable().
+ *
+ * The Tag check override (TCO) bit disables temporarily the tag checking
+ * preventing the issue.
+ */
+static inline void mte_disable_tco(void)
+{
+	asm volatile(ALTERNATIVE("nop", SET_PSTATE_TCO(0),
+				 ARM64_MTE, CONFIG_KASAN_HW_TAGS));
+}
+
+static inline void mte_enable_tco(void)
+{
+	asm volatile(ALTERNATIVE("nop", SET_PSTATE_TCO(1),
+				 ARM64_MTE, CONFIG_KASAN_HW_TAGS));
+}
+
+/*
+ * These functions disable tag checking only if in MTE async mode
+ * since the sync mode generates exceptions synchronously and the
+ * nofault or load_unaligned_zeropad can handle them.
+ */
+static inline void __mte_disable_tco_async(void)
+{
+	if (system_uses_mte_async_or_asymm_mode())
+		mte_disable_tco();
+}
+
+static inline void __mte_enable_tco_async(void)
+{
+	if (system_uses_mte_async_or_asymm_mode())
+		mte_enable_tco();
+}
+
+/*
+ * 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> */
+	u8 tag = 0xF0 | (u8)(((u64)(ptr)) >> MTE_TAG_SHIFT);
+
+	return tag;
+}
+
+/* Get allocation tag for the address. */
+static inline u8 mte_get_mem_tag(void *addr)
+{
+	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);
+}
+
+static inline u64 __stg_post(u64 p)
+{
+	asm volatile(__MTE_PREAMBLE "stg %0, [%0], #16"
+		     : "+r"(p)
+		     :
+		     : "memory");
+	return p;
+}
+
+static inline u64 __stzg_post(u64 p)
+{
+	asm volatile(__MTE_PREAMBLE "stzg %0, [%0], #16"
+		     : "+r"(p)
+		     :
+		     : "memory");
+	return p;
+}
+
+static inline void __dc_gva(u64 p)
+{
+	asm volatile(__MTE_PREAMBLE "dc gva, %0" : : "r"(p) : "memory");
+}
+
+static inline void __dc_gzva(u64 p)
+{
+	asm volatile(__MTE_PREAMBLE "dc gzva, %0" : : "r"(p) : "memory");
+}
+
+/*
+ * 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 MTE_GRANULE_SIZE aligned.
+ */
+static inline void mte_set_mem_tag_range(void *addr, size_t size, u8 tag,
+					 bool init)
+{
+	u64 curr, mask, dczid, dczid_bs, dczid_dzp, end1, end2, end3;
+
+	/* Read DC G(Z)VA block size from the system register. */
+	dczid = read_cpuid(DCZID_EL0);
+	dczid_bs = 4ul << (dczid & 0xf);
+	dczid_dzp = (dczid >> 4) & 1;
+
+	curr = (u64)__tag_set(addr, tag);
+	mask = dczid_bs - 1;
+	/* STG/STZG up to the end of the first block. */
+	end1 = curr | mask;
+	end3 = curr + size;
+	/* DC GVA / GZVA in [end1, end2) */
+	end2 = end3 & ~mask;
+
+	/*
+	 * The following code uses STG on the first DC GVA block even if the
+	 * start address is aligned - it appears to be faster than an alignment
+	 * check + conditional branch. Also, if the range size is at least 2 DC
+	 * GVA blocks, the first two loops can use post-condition to save one
+	 * branch each.
+	 */
+#define SET_MEMTAG_RANGE(stg_post, dc_gva)		\
+	do {						\
+		if (!dczid_dzp && size >= 2 * dczid_bs) {\
+			do {				\
+				curr = stg_post(curr);	\
+			} while (curr < end1);		\
+							\
+			do {				\
+				dc_gva(curr);		\
+				curr += dczid_bs;	\
+			} while (curr < end2);		\
+		}					\
+							\
+		while (curr < end3)			\
+			curr = stg_post(curr);		\
+	} while (0)
+
+	if (init)
+		SET_MEMTAG_RANGE(__stzg_post, __dc_gzva);
+	else
+		SET_MEMTAG_RANGE(__stg_post, __dc_gva);
+#undef SET_MEMTAG_RANGE
+}
+
+void mte_enable_kernel_sync(void);
+void mte_enable_kernel_async(void);
+void mte_enable_kernel_asymm(void);
+
+#else /* CONFIG_ARM64_MTE */
+
+static inline void mte_disable_tco(void)
+{
+}
+
+static inline void mte_enable_tco(void)
+{
+}
+
+static inline void __mte_disable_tco_async(void)
+{
+}
+
+static inline void __mte_enable_tco_async(void)
+{
+}
+
+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, bool init)
+{
+}
+
+static inline void mte_enable_kernel_sync(void)
+{
+}
+
+static inline void mte_enable_kernel_async(void)
+{
+}
+
+static inline void mte_enable_kernel_asymm(void)
+{
+}
+
+#endif /* CONFIG_ARM64_MTE */
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* __ASM_MTE_KASAN_H  */