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From:   Nam Cao <namcaov@gmail.com>
To:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     Nam Cao <namcaov@gmail.com>
Subject: [PATCH 2/3] riscv: kprobes: simulate c.jr and c.jalr instructions
Date:   Sun, 30 Jul 2023 10:27:08 +0200
Message-Id: <db8b7787e9208654cca50484f68334f412be2ea9.1690704360.git.namcaov@gmail.com>
In-Reply-To: <cover.1690704360.git.namcaov@gmail.com>
References: <cover.1690704360.git.namcaov@gmail.com>
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kprobes currently rejects c.jr and c.jalr instructions. Implement them.

Signed-off-by: Nam Cao <namcaov@gmail.com>
---
 arch/riscv/kernel/probes/decode-insn.c   |  4 +--
 arch/riscv/kernel/probes/simulate-insn.c | 37 ++++++++++++++++++++++++
 arch/riscv/kernel/probes/simulate-insn.h |  2 ++
 3 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
index 39adb07a342d..6dba23a55ac7 100644
--- a/arch/riscv/kernel/probes/decode-insn.c
+++ b/arch/riscv/kernel/probes/decode-insn.c
@@ -29,14 +29,14 @@ riscv_probe_decode_insn(probe_opcode_t *addr, struct arch_probe_insn *api)
 	 * TODO: the REJECTED ones below need to be implemented
 	 */
 #ifdef CONFIG_RISCV_ISA_C
-	RISCV_INSN_REJECTED(c_jr,		insn);
 	RISCV_INSN_REJECTED(c_jal,		insn);
-	RISCV_INSN_REJECTED(c_jalr,		insn);
 	RISCV_INSN_REJECTED(c_beqz,		insn);
 	RISCV_INSN_REJECTED(c_bnez,		insn);
 	RISCV_INSN_REJECTED(c_ebreak,		insn);
 
 	RISCV_INSN_SET_SIMULATE(c_j,		insn);
+	RISCV_INSN_SET_SIMULATE(c_jr,		insn);
+	RISCV_INSN_SET_SIMULATE(c_jalr,		insn);
 #endif
 
 	RISCV_INSN_SET_SIMULATE(jal,		insn);
diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
index 3ba45c612cd8..1ead6f4951f9 100644
--- a/arch/riscv/kernel/probes/simulate-insn.c
+++ b/arch/riscv/kernel/probes/simulate-insn.c
@@ -212,3 +212,40 @@ bool __kprobes simulate_c_j(u32 opcode, unsigned long addr, struct pt_regs *regs
 
 	return true;
 }
+
+static bool __kprobes simulate_c_jr_jalr(u32 opcode, unsigned long addr, struct pt_regs *regs,
+					 bool is_jalr)
+{
+	/*
+	 *  15    12 11  7 6   2 1  0
+	 * | funct4 | rs1 | rs2 | op |
+	 *     4       5     5    2
+	 */
+
+	unsigned long jump_addr;
+
+	u32 rs1 = (opcode >> 7) & 0x1f;
+
+	if (rs1 == 0) /* C.JR is only valid when rs1 != x0 */
+		return false;
+
+	if (!rv_insn_reg_get_val(regs, rs1, &jump_addr))
+		return false;
+
+	if (is_jalr && !rv_insn_reg_set_val(regs, 1, addr + 2))
+		return false;
+
+	instruction_pointer_set(regs, jump_addr);
+
+	return true;
+}
+
+bool __kprobes simulate_c_jr(u32 opcode, unsigned long addr, struct pt_regs *regs)
+{
+	return simulate_c_jr_jalr(opcode, addr, regs, false);
+}
+
+bool __kprobes simulate_c_jalr(u32 opcode, unsigned long addr, struct pt_regs *regs)
+{
+	return simulate_c_jr_jalr(opcode, addr, regs, true);
+}
diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
index 4bd6c266e7d3..472a1948ec4f 100644
--- a/arch/riscv/kernel/probes/simulate-insn.h
+++ b/arch/riscv/kernel/probes/simulate-insn.h
@@ -25,5 +25,7 @@ bool simulate_branch(u32 opcode, unsigned long addr, struct pt_regs *regs);
 bool simulate_jal(u32 opcode, unsigned long addr, struct pt_regs *regs);
 bool simulate_jalr(u32 opcode, unsigned long addr, struct pt_regs *regs);
 bool simulate_c_j(u32 opcode, unsigned long addr, struct pt_regs *regs);
+bool simulate_c_jr(u32 opcode, unsigned long addr, struct pt_regs *regs);
+bool simulate_c_jalr(u32 opcode, unsigned long addr, struct pt_regs *regs);
 
 #endif /* _RISCV_KERNEL_PROBES_SIMULATE_INSN_H */
-- 
2.34.1