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-rw-r--r--kernel/kcsan/encoding.h95
1 files changed, 95 insertions, 0 deletions
diff --git a/kernel/kcsan/encoding.h b/kernel/kcsan/encoding.h
new file mode 100644
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--- /dev/null
+++ b/kernel/kcsan/encoding.h
@@ -0,0 +1,95 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _KERNEL_KCSAN_ENCODING_H
+#define _KERNEL_KCSAN_ENCODING_H
+
+#include <linux/bits.h>
+#include <linux/log2.h>
+#include <linux/mm.h>
+
+#include "kcsan.h"
+
+#define SLOT_RANGE PAGE_SIZE
+
+#define INVALID_WATCHPOINT 0
+#define CONSUMED_WATCHPOINT 1
+
+/*
+ * The maximum useful size of accesses for which we set up watchpoints is the
+ * max range of slots we check on an access.
+ */
+#define MAX_ENCODABLE_SIZE (SLOT_RANGE * (1 + KCSAN_CHECK_ADJACENT))
+
+/*
+ * Number of bits we use to store size info.
+ */
+#define WATCHPOINT_SIZE_BITS bits_per(MAX_ENCODABLE_SIZE)
+/*
+ * This encoding for addresses discards the upper (1 for is-write + SIZE_BITS);
+ * however, most 64-bit architectures do not use the full 64-bit address space.
+ * Also, in order for a false positive to be observable 2 things need to happen:
+ *
+ * 1. different addresses but with the same encoded address race;
+ * 2. and both map onto the same watchpoint slots;
+ *
+ * Both these are assumed to be very unlikely. However, in case it still happens
+ * happens, the report logic will filter out the false positive (see report.c).
+ */
+#define WATCHPOINT_ADDR_BITS (BITS_PER_LONG-1 - WATCHPOINT_SIZE_BITS)
+
+/*
+ * Masks to set/retrieve the encoded data.
+ */
+#define WATCHPOINT_WRITE_MASK BIT(BITS_PER_LONG-1)
+#define WATCHPOINT_SIZE_MASK \
+ GENMASK(BITS_PER_LONG-2, BITS_PER_LONG-2 - WATCHPOINT_SIZE_BITS)
+#define WATCHPOINT_ADDR_MASK \
+ GENMASK(BITS_PER_LONG-3 - WATCHPOINT_SIZE_BITS, 0)
+
+static inline bool check_encodable(unsigned long addr, size_t size)
+{
+ return size <= MAX_ENCODABLE_SIZE;
+}
+
+static inline long
+encode_watchpoint(unsigned long addr, size_t size, bool is_write)
+{
+ return (long)((is_write ? WATCHPOINT_WRITE_MASK : 0) |
+ (size << WATCHPOINT_ADDR_BITS) |
+ (addr & WATCHPOINT_ADDR_MASK));
+}
+
+static __always_inline bool decode_watchpoint(long watchpoint,
+ unsigned long *addr_masked,
+ size_t *size,
+ bool *is_write)
+{
+ if (watchpoint == INVALID_WATCHPOINT ||
+ watchpoint == CONSUMED_WATCHPOINT)
+ return false;
+
+ *addr_masked = (unsigned long)watchpoint & WATCHPOINT_ADDR_MASK;
+ *size = ((unsigned long)watchpoint & WATCHPOINT_SIZE_MASK) >> WATCHPOINT_ADDR_BITS;
+ *is_write = !!((unsigned long)watchpoint & WATCHPOINT_WRITE_MASK);
+
+ return true;
+}
+
+/*
+ * Return watchpoint slot for an address.
+ */
+static __always_inline int watchpoint_slot(unsigned long addr)
+{
+ return (addr / PAGE_SIZE) % CONFIG_KCSAN_NUM_WATCHPOINTS;
+}
+
+static __always_inline bool matching_access(unsigned long addr1, size_t size1,
+ unsigned long addr2, size_t size2)
+{
+ unsigned long end_range1 = addr1 + size1 - 1;
+ unsigned long end_range2 = addr2 + size2 - 1;
+
+ return addr1 <= end_range2 && addr2 <= end_range1;
+}
+
+#endif /* _KERNEL_KCSAN_ENCODING_H */

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