[PATCH 3/3] riscv: kprobes: simulate c.beqz and c.bnez

[Charlie Jenkins]

On Sun, Jul 30, 2023 at 10:27:09AM +0200, Nam Cao wrote:
> kprobes currently rejects instruction c.beqz and c.bnez. Implement them.
> 
> Signed-off-by: Nam Cao <namcaov at gmail.com>
> ---
>  arch/riscv/kernel/probes/decode-insn.c   |  4 +--
>  arch/riscv/kernel/probes/simulate-insn.c | 44 ++++++++++++++++++++++++
>  arch/riscv/kernel/probes/simulate-insn.h |  2 ++
>  3 files changed, 48 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
> index 6dba23a55ac7..65d9590bfb9f 100644
> --- a/arch/riscv/kernel/probes/decode-insn.c
> +++ b/arch/riscv/kernel/probes/decode-insn.c
> @@ -30,13 +30,13 @@ riscv_probe_decode_insn(probe_opcode_t *addr, struct arch_probe_insn *api)
>  	 */
>  #ifdef CONFIG_RISCV_ISA_C
>  	RISCV_INSN_REJECTED(c_jal,		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);
> +	RISCV_INSN_SET_SIMULATE(c_beqz,		insn);
> +	RISCV_INSN_SET_SIMULATE(c_bnez,		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 1ead6f4951f9..d3099d67816d 100644
> --- a/arch/riscv/kernel/probes/simulate-insn.c
> +++ b/arch/riscv/kernel/probes/simulate-insn.c
> @@ -249,3 +249,47 @@ bool __kprobes simulate_c_jalr(u32 opcode, unsigned long addr, struct pt_regs *r
>  {
>  	return simulate_c_jr_jalr(opcode, addr, regs, true);
>  }
> +
> +static bool __kprobes simulate_c_bnez_beqz(u32 opcode, unsigned long addr, struct pt_regs *regs,
> +					   bool is_bnez)
> +{
> +	/*
> +	 *  15    13 12           10 9    7 6                 2 1  0
> +	 * | funct3 | offset[8|4:3] | rs1' | offset[7:6|2:1|5] | op |
> +	 *     3            3          3             5           2
> +	 */
> +
> +	s32 offset;
> +	u32 rs1;
> +	unsigned long rs1_val;
> +
> +	rs1 = 0x8 | ((opcode >> 7) & 0x7);
> +
> +	if (!rv_insn_reg_get_val(regs, rs1, &rs1_val))
> +		return false;
> +
> +	if ((rs1_val != 0 && is_bnez) || (rs1_val == 0 && !is_bnez)) {
> +		offset =  ((opcode >> 3)  & 0x3) << 1;
> +		offset |= ((opcode >> 10) & 0x3) << 3;
> +		offset |= ((opcode >> 2)  & 0x1) << 5;
> +		offset |= ((opcode >> 5)  & 0x3) << 6;
> +		offset |= ((opcode >> 12) & 0x1) << 8;
> +		offset = sign_extend32(offset, 8);
> +	} else {
> +		offset = 2;
> +	}
> +
> +	instruction_pointer_set(regs, addr + offset);
> +
> +	return true;
> +}
> +
> +bool __kprobes simulate_c_bnez(u32 opcode, unsigned long addr, struct pt_regs *regs)
> +{
> +	return simulate_c_bnez_beqz(opcode, addr, regs, true);
> +}
> +
> +bool __kprobes simulate_c_beqz(u32 opcode, unsigned long addr, struct pt_regs *regs)
> +{
> +	return simulate_c_bnez_beqz(opcode, addr, regs, false);
> +}
> diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
> index 472a1948ec4f..44ebbc444db9 100644
> --- a/arch/riscv/kernel/probes/simulate-insn.h
> +++ b/arch/riscv/kernel/probes/simulate-insn.h
> @@ -27,5 +27,7 @@ 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);
> +bool simulate_c_bnez(u32 opcode, unsigned long addr, struct pt_regs *regs);
> +bool simulate_c_beqz(u32 opcode, unsigned long addr, struct pt_regs *regs);
>  
>  #endif /* _RISCV_KERNEL_PROBES_SIMULATE_INSN_H */
> -- 
> 2.34.1
> 
> 
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Reviewed-by: Charlie Jenkins <charlie at rivosinc.com>