linux-kernel - Re: [PATCH] riscv/ptrace: add new regset to get original a0 register

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Message-ID: <87v7w22ip6.fsf@all.your.base.are.belong.to.us>
Date: Mon, 02 Dec 2024 16:44:21 +0100
From: Björn Töpel <bjorn@...nel.org>
To: Celeste Liu <uwu@...lacanthus.name>, Oleg Nesterov <oleg@...hat.com>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Eric Biederman
 <ebiederm@...ssion.com>, Kees Cook <kees@...nel.org>
Cc: Alexandre Ghiti <alex@...ti.fr>, "Dmitry V. Levin" <ldv@...ace.io>,
 Andrea Bolognani <abologna@...hat.com>, Thomas Gleixner
 <tglx@...utronix.de>, Ron Economos <re@...z.net>, Felix Yan
 <felixonmars@...hlinux.org>, Ruizhe Pan <c141028@...il.com>, Shiqi Zhang
 <shiqi@...c.iscas.ac.cn>, Guo Ren <guoren@...nel.org>, Yao Zi
 <ziyao@...root.org>, Han Gao <gaohan@...as.ac.cn>,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, stable@...r.kernel.org, Celeste Liu
 <uwu@...lacanthus.name>
Subject: Re: [PATCH] riscv/ptrace: add new regset to get original a0 register

Thanks for working on this!

Celeste Liu <uwu@...lacanthus.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/
> Signed-off-by: Celeste Liu <uwu@...lacanthus.name>
> ---
>  arch/riscv/kernel/ptrace.c | 33 +++++++++++++++++++++++++++++++++
>  include/uapi/linux/elf.h   |  1 +
>  2 files changed, 34 insertions(+)
>
> diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
> index ea67e9fb7a583683b922fe2c017ea61f3bc848db..faa46de9000376eb445a32d43a40210d7b846844 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 +185,30 @@ 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)

Use full 100 chars!

> +{
> +	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)

Dito!

> +{
> +	int orig_a0 = task_pt_regs(target)->orig_a0;

64b regs on RV64.

> +	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;
> +}
> +
> +

Multiple blanks.

>  static const struct user_regset riscv_user_regset[] = {
>  	[REGSET_X] = {
>  		.core_note_type = NT_PRSTATUS,
> @@ -224,6 +249,14 @@ static const struct user_regset riscv_user_regset[] = {
>  		.set = tagged_addr_ctrl_set,
>  	},
>  #endif
> +	[REGSET_ORIG_A0] = {
> +		.core_note_type = NT_RISCV_ORIG_A0,
> +		.n = 1,
> +		.size = sizeof(elf_greg_t),
> +		.align = sizeof(elf_greg_t),

...and sizeof(elf_greg_t) is 64b in RV64 -- mismatch above.

Björn