Re: [PATCH v2 1/2] riscv/ptrace: add new regset to access original a0 register

["Björn Töpel" <bjorn@kernel.org>]

Celeste Liu <uwu@coelacanthus.name> writes:

> The orig_a0 is missing in struct user_regs_struct of riscv, and there is
> no way to add it without breaking UAPI. (See Link tag below)
>
> Like NT_ARM_SYSTEM_CALL do, we add a new regset name NT_RISCV_ORIG_A0 to
> access original a0 register from userspace via ptrace API.
>
> Link: https://lore.kernel.org/all/59505464-c84a-403d-972f-d4b2055eeaac@gmail.com/
> Cc: stable@vger.kernel.org
> Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
> ---
>  arch/riscv/kernel/ptrace.c | 32 ++++++++++++++++++++++++++++++++
>  include/uapi/linux/elf.h   |  1 +
>  2 files changed, 33 insertions(+)
>
> diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
> index ea67e9fb7a583683b922fe2c017ea61f3bc848db..18ce07ffb27bb1180667769eed800f6fdf96c083 100644
> --- a/arch/riscv/kernel/ptrace.c
> +++ b/arch/riscv/kernel/ptrace.c
> @@ -31,6 +31,7 @@ enum riscv_regset {
>  #ifdef CONFIG_RISCV_ISA_SUPM
>  	REGSET_TAGGED_ADDR_CTRL,
>  #endif
> +	REGSET_ORIG_A0,
>  };
>  
>  static int riscv_gpr_get(struct task_struct *target,
> @@ -184,6 +185,29 @@ static int tagged_addr_ctrl_set(struct task_struct *target,
>  }
>  #endif
>  
> +static int riscv_orig_a0_get(struct task_struct *target,
> +			     const struct user_regset *regset,
> +			     struct membuf to)
> +{
> +	return membuf_store(&to, task_pt_regs(target)->orig_a0);
> +}
> +
> +static int riscv_orig_a0_set(struct task_struct *target,
> +			     const struct user_regset *regset,
> +			     unsigned int pos, unsigned int count,
> +			     const void *kbuf, const void __user *ubuf)
> +{
> +	unsigned long orig_a0 = task_pt_regs(target)->orig_a0;
> +	int ret;
> +
> +	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &orig_a0, 0, -1);
> +	if (ret)
> +		return ret;
> +
> +	task_pt_regs(target)->orig_a0 = orig_a0;
> +	return ret;

Nit: Could be return 0, for readability.

Regardless,
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>