linux-kernel - Re: [PATCH v3] mm/madvise: unrestrict process

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Message-ID: <b04ecc20-3bd2-488a-b8c5-0599acdd0828@lucifer.local>
Date: Thu, 26 Sep 2024 17:36:31 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Suren Baghdasaryan <surenb@...gle.com>, Arnd Bergmann <arnd@...db.de>,
        linux-api@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Minchan Kim <minchan@...nel.org>,
        Christian Brauner <brauner@...nel.org>, pedro.falcato@...il.com
Subject: Re: [PATCH v3] mm/madvise: unrestrict process_madvise() for current
 process

On Thu, Sep 26, 2024 at 08:52:32AM GMT, Shakeel Butt wrote:
> On Thu, Sep 26, 2024 at 04:10:19PM GMT, Lorenzo Stoakes wrote:
> > The process_madvise() call was introduced in commit ecb8ac8b1f14
> > ("mm/madvise: introduce process_madvise() syscall: an external memory
> > hinting API") as a means of performing madvise() operations on another
> > process.
> >
> > However, as it provides the means by which to perform multiple madvise()
> > operations in a batch via an iovec, it is useful to utilise the same
> > interface for performing operations on the current process rather than a
> > remote one.
> >
> > Commit 22af8caff7d1 ("mm/madvise: process_madvise() drop capability check
> > if same mm") removed the need for a caller invoking process_madvise() on
> > its own pidfd to possess the CAP_SYS_NICE capability, however this leaves
> > the restrictions on operation in place.
> >
> > Resolve this by only applying the restriction on operations when accessing
> > a remote process.
> >
> > Moving forward we plan to implement a simpler means of specifying this
> > condition other than needing to establish a self pidfd, perhaps in the form
> > of a sentinel pidfd.
> >
> > Also take the opportunity to refactor the system call implementation
> > abstracting the vectorised operation.
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
>
> Acked-by: Shakeel Butt <shakeel.butt@...ux.dev>

Thanks!

>
> > ---
> > v3:
> > * Avoid introducing PR_MADV_SELF and defer a non-pidfd version until later.
>
> Seems like a good plan to decouple this patch from PR_MADV_SELF vs
> PIDFD_SELF decision. I am hoping to see the follow up patch as well.
>
> thanks,
> Shakeel
>

Yes agreed, this gets an important part of the change in, and gives us room
to take our time on that side of things.

Plan right now is I will work on a sentinel solution in parallel to other
stuff and see how that goes, if it integrates well can bring it in in a
separate patch series.

Cheers, Lorenzo