1 files changed, 77 insertions, 0 deletions
diff --git a/arch/riscv/kernel/cfi.c b/arch/riscv/kernel/cfi.c
new file mode 100644
index 000000000000..820158d7a291
--- /dev/null
+++ b/arch/riscv/kernel/cfi.c
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Clang Control Flow Integrity (CFI) support.
+ *
+ * Copyright (C) 2023 Google LLC
+ */
+#include <asm/cfi.h>
+#include <asm/insn.h>
+
+/*
+ * Returns the target address and the expected type when regs->epc points
+ * to a compiler-generated CFI trap.
+ */
+static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target,
+			    u32 *type)
+{
+	unsigned long *regs_ptr = (unsigned long *)regs;
+	int rs1_num;
+	u32 insn;
+
+	*target = *type = 0;
+
+	/*
+	 * The compiler generates the following instruction sequence
+	 * for indirect call checks:
+	 *
+	 *   lw      t1, -4(<reg>)
+	 *   lui     t2, <hi20>
+	 *   addiw   t2, t2, <lo12>
+	 *   beq     t1, t2, .Ltmp1
+	 *   ebreak  ; <- regs->epc
+	 *   .Ltmp1:
+	 *   jalr    <reg>
+	 *
+	 * We can read the expected type and the target address from the
+	 * registers passed to the beq/jalr instructions.
+	 */
+	if (get_kernel_nofault(insn, (void *)regs->epc - 4))
+		return false;
+	if (!riscv_insn_is_beq(insn))
+		return false;
+
+	*type = (u32)regs_ptr[RV_EXTRACT_RS1_REG(insn)];
+
+	if (get_kernel_nofault(insn, (void *)regs->epc) ||
+	    get_kernel_nofault(insn, (void *)regs->epc + GET_INSN_LENGTH(insn)))
+		return false;
+
+	if (riscv_insn_is_jalr(insn))
+		rs1_num = RV_EXTRACT_RS1_REG(insn);
+	else if (riscv_insn_is_c_jalr(insn))
+		rs1_num = RVC_EXTRACT_C2_RS1_REG(insn);
+	else
+		return false;
+
+	*target = regs_ptr[rs1_num];
+
+	return true;
+}
+
+/*
+ * Checks if the ebreak trap is because of a CFI failure, and handles the trap
+ * if needed. Returns a bug_trap_type value similarly to report_bug.
+ */
+enum bug_trap_type handle_cfi_failure(struct pt_regs *regs)
+{
+	unsigned long target;
+	u32 type;
+
+	if (!is_cfi_trap(regs->epc))
+		return BUG_TRAP_TYPE_NONE;
+
+	if (!decode_cfi_insn(regs, &target, &type))
+		return report_cfi_failure_noaddr(regs, regs->epc);
+
+	return report_cfi_failure(regs, regs->epc, &target, type);
+}