linux-kernel - [PATCH 1/3] riscv: kprobes: simulate c.j instruction

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Message-Id: <6ef76cd9984b8015826649d13f870f8ac45a2d0d.1690704360.git.namcaov@gmail.com>
Date:   Sun, 30 Jul 2023 10:27:07 +0200
From:   Nam Cao <namcaov@...il.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Nam Cao <namcaov@...il.com>
Subject: [PATCH 1/3] riscv: kprobes: simulate c.j instruction

kprobes currently rejects c.j instruction. Implement it.

Signed-off-by: Nam Cao <namcaov@...il.com>
---
 arch/riscv/kernel/probes/decode-insn.c   |  3 ++-
 arch/riscv/kernel/probes/simulate-insn.c | 24 ++++++++++++++++++++++++
 arch/riscv/kernel/probes/simulate-insn.h |  1 +
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
index 64f6183b4717..39adb07a342d 100644
--- a/arch/riscv/kernel/probes/decode-insn.c
+++ b/arch/riscv/kernel/probes/decode-insn.c
@@ -29,13 +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_j,		insn);
 	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);
 #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 7441ac8a6843..3ba45c612cd8 100644
--- a/arch/riscv/kernel/probes/simulate-insn.c
+++ b/arch/riscv/kernel/probes/simulate-insn.c
@@ -188,3 +188,27 @@ bool __kprobes simulate_branch(u32 opcode, unsigned long addr, struct pt_regs *r
 
 	return true;
 }
+
+bool __kprobes simulate_c_j(u32 opcode, unsigned long addr, struct pt_regs *regs)
+{
+	/*
+	 *  15    13 12                            2 1      0
+	 * | funct3 | offset[11|4|9:8|10|6|7|3:1|5] | opcode |
+	 *     3                   11                    2
+	 */
+
+	s32 offset;
+
+	offset  = ((opcode >> 3)  & 0x7) << 1;
+	offset |= ((opcode >> 11) & 0x1) << 4;
+	offset |= ((opcode >> 2)  & 0x1) << 5;
+	offset |= ((opcode >> 7)  & 0x1) << 6;
+	offset |= ((opcode >> 6)  & 0x1) << 7;
+	offset |= ((opcode >> 9)  & 0x3) << 8;
+	offset |= ((opcode >> 8)  & 0x1) << 10;
+	offset |= ((opcode >> 12) & 0x1) << 11;
+
+	instruction_pointer_set(regs, addr + sign_extend32(offset, 11));
+
+	return true;
+}
diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
index 61e35db31001..4bd6c266e7d3 100644
--- a/arch/riscv/kernel/probes/simulate-insn.h
+++ b/arch/riscv/kernel/probes/simulate-insn.h
@@ -24,5 +24,6 @@ bool simulate_auipc(u32 opcode, unsigned long addr, struct pt_regs *regs);
 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);
 
 #endif /* _RISCV_KERNEL_PROBES_SIMULATE_INSN_H */
-- 
2.34.1