linux-kernel - Re: [RFC PATCH v4 01/13] ptrace: Use regset

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Date:   Wed, 27 May 2020 14:34:05 +0800
From:   Greentime Hu <greentime.hu@...ive.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Guo Ren <guoren@...ux.alibaba.com>,
        Vincent Chen <vincent.chen@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v4 01/13] ptrace: Use regset_size() for dynamic regset size.

Oleg Nesterov <oleg@...hat.com> 於 2020年5月26日 週二 下午10:00寫道：
>
> On 05/26, Greentime Hu wrote:
> >
> > @@ -882,13 +882,18 @@ static int ptrace_regset(struct task_struct *task, int req, unsigned int type,
> >       const struct user_regset_view *view = task_user_regset_view(task);
> >       const struct user_regset *regset = find_regset(view, type);
> >       int regset_no;
> > +     unsigned int size;
> >
> > -     if (!regset || (kiov->iov_len % regset->size) != 0)
> > +     if (!regset)
> >               return -EINVAL;
> >
> >       regset_no = regset - view->regsets;
> > -     kiov->iov_len = min(kiov->iov_len,
> > -                         (__kernel_size_t) (regset->n * regset->size));
> > +     size = regset_size(task, regset);
> > +
> > +     if ((kiov->iov_len % size) != 0)
> > +             return -EINVAL;
>
> Hmm. this doesn't look right.
>
> Before this patch we check "iov_len % regset->size", this is not the same
> as "iov_len % regset_size()".
>
> IOW, currently you can read/write, say, only the 1st register, you patch
> breaks this?
>

Hi Oleg,

Thank you. I misunderstood the meaning of regset->size
It seems I only needs to update this line, right?
- kiov->iov_len = min(kiov->iov_len,  (__kernel_size_t) (regset->n *
regset->size));
+ kiov->iov_len = min(kiov->iov_len,  (__kernel_size_t)
regset_size(task, regset));