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

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Date:   Fri, 26 Feb 2021 17:04:25 +0100
From:   Michał Mirosław <emmir@...gle.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Piotr Figiel <figiel@...gle.com>,
        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>,
        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 Fri, 26 Feb 2021 at 16:32, Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
>
> ----- 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 ?

In this case returning sizeof(conf) would serve the same purpose, wouldn't it?

Best Regards
Michał Mirosław

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