linux-kernel - Re: [PATCH] ptrace: add PTRACE_GET_RSEQ

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Date:   Mon, 22 Feb 2021 14:57:26 +0300
From:   "Dmitry V. Levin" <ldv@...linux.org>
To:     Piotr Figiel <figiel@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        mathieu.desnoyers@...icios.com, peterz@...radead.org,
        paulmck@...nel.org, boqun.feng@...il.com, oleg@...hat.com,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrei Vagin <avagin@...il.com>, linux-kernel@...r.kernel.org,
        posk@...gle.com, kyurtsever@...gle.com, ckennelly@...gle.com,
        pjt@...gle.com, emmir@...gle.com, linux-man@...r.kernel.org,
        linux-api@...r.kernel.org
Subject: Re: [PATCH] ptrace: add PTRACE_GET_RSEQ_CONFIGURATION request

On Mon, Feb 22, 2021 at 11:04:43AM +0100, Piotr Figiel wrote:
[...]
> --- a/include/uapi/linux/ptrace.h
> +++ b/include/uapi/linux/ptrace.h
> @@ -102,6 +102,14 @@ struct ptrace_syscall_info {
>  	};
>  };
>  
> +#define PTRACE_GET_RSEQ_CONFIGURATION	0x420f
> +
> +struct ptrace_rseq_configuration {
> +	__u64 rseq_abi_pointer;
> +	__u32 signature;
> +	__u32 pad;
> +};
> +
>  /*
>   * These values are stored in task->ptrace_message
>   * by tracehook_report_syscall_* to describe the current syscall-stop.
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 61db50f7ca86..a936af66cf6f 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -31,6 +31,7 @@
>  #include <linux/cn_proc.h>
>  #include <linux/compat.h>
>  #include <linux/sched/signal.h>
> +#include <linux/minmax.h>
>  
>  #include <asm/syscall.h>	/* for syscall_get_* */
>  
> @@ -779,6 +780,22 @@ static int ptrace_peek_siginfo(struct task_struct *child,
>  	return ret;
>  }
>  
> +#ifdef CONFIG_RSEQ
> +static long ptrace_get_rseq_configuration(struct task_struct *task,
> +					  unsigned long size, void __user *data)
> +{
> +	struct ptrace_rseq_configuration conf = {
> +		.rseq_abi_pointer = (u64)(uintptr_t)task->rseq,
> +		.signature = task->rseq_sig,
> +	};
> +
> +	size = min_t(unsigned long, size, sizeof(conf));
> +	if (copy_to_user(data, &conf, size))
> +		return -EFAULT;
> +	return size;
> +}
> +#endif

>From API perspective I suggest for such interfaces to return the amount of
data that could have been written if there was enough room specified, e.g.
in this case it's sizeof(conf) instead of size.


-- 
ldv