linux-kernel - Re: [PATCH v2] ptrace: add PTRACE_GET_RSEQ

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Date:   Fri, 26 Feb 2021 10:32:35 -0500 (EST)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Piotr Figiel <figiel@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        paulmck <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        Florian Weimer <fweimer@...hat.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrei Vagin <avagin@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Peter Oskolkov <posk@...gle.com>,
        Kamil Yurtsever <kyurtsever@...gle.com>,
        Chris Kennelly <ckennelly@...gle.com>,
        Paul Turner <pjt@...gle.com>, emmir <emmir@...gle.com>,
        linux-man <linux-man@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2] ptrace: add PTRACE_GET_RSEQ_CONFIGURATION request

----- On Feb 26, 2021, at 8:51 AM, Piotr Figiel figiel@...gle.com wrote:
[...]
> ---
> v2:
> Applied review comments:
> - changed return value from the ptrace request to the size of the
>   configuration structure
> - expanded configuration structure with the flags field and
>   the rseq abi structure size
> 
[...]
> +#define PTRACE_GET_RSEQ_CONFIGURATION	0x420f
> +
> +struct ptrace_rseq_configuration {
> +	__u64 rseq_abi_pointer;
> +	__u32 rseq_abi_size;
> +	__u32 signature;
> +	__u32 flags;
> +	__u32 pad;
> +};
> +
[...]
> +#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,
> +		.rseq_abi_size = sizeof(*task->rseq),
> +		.signature = task->rseq_sig,
> +		.flags = 0,
> +	};
> +
> +	size = min_t(unsigned long, size, sizeof(conf));
> +	if (copy_to_user(data, &conf, size))
> +		return -EFAULT;
> +	return sizeof(conf);
> +}

I think what Florian was after would be:

struct ptrace_rseq_configuration {
	__u32 size;  /* size of struct ptrace_rseq_configuration */
	__u32 flags;
	__u64 rseq_abi_pointer;
	__u32 signature;
	__u32 pad;
};

where:

    .size = sizeof(struct ptrace_rseq_configuration),

This way, the configuration structure can be expanded in the future. The
rseq ABI structure is by definition fixed-size, so there is no point in
having its size here.

Florian, did I understand your request correctly, or am I missing your point ?

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com