From: Matthew Wilcox <willy@infradead.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: "Weiny, Ira" <ira.weiny@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
Dave Hansen <dave.hansen@intel.com>,
Christoph Hellwig <hch@infradead.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Eric Biggers <ebiggers@kernel.org>,
Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH V2 2/2] mm/highmem: Lift memcpy_[to|from]_page to core
Date: Mon, 7 Dec 2020 23:40:08 +0000 [thread overview]
Message-ID: <20201207234008.GE7338@casper.infradead.org> (raw)
In-Reply-To: <CAPcyv4hkY-9V5Rq5s=BRku2AeWYtgs9DuVXnhdEkara2NiN9Tg@mail.gmail.com>
On Mon, Dec 07, 2020 at 03:34:44PM -0800, Dan Williams wrote:
> On Mon, Dec 7, 2020 at 3:27 PM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Mon, Dec 07, 2020 at 02:57:03PM -0800, ira.weiny@intel.com wrote:
> > > +static inline void memcpy_page(struct page *dst_page, size_t dst_off,
> > > + struct page *src_page, size_t src_off,
> > > + size_t len)
> > > +{
> > > + char *dst = kmap_local_page(dst_page);
> > > + char *src = kmap_local_page(src_page);
> >
> > I appreciate you've only moved these, but please add:
> >
> > BUG_ON(dst_off + len > PAGE_SIZE || src_off + len > PAGE_SIZE);
>
> I imagine it's not outside the realm of possibility that some driver
> on CONFIG_HIGHMEM=n is violating this assumption and getting away with
> it because kmap_atomic() of contiguous pages "just works (TM)".
> Shouldn't this WARN rather than BUG so that the user can report the
> buggy driver and not have a dead system?
As opposed to (on a HIGHMEM=y system) silently corrupting data that
is on the next page of memory? I suppose ideally ...
if (WARN_ON(dst_off + len > PAGE_SIZE))
len = PAGE_SIZE - dst_off;
if (WARN_ON(src_off + len > PAGE_SIZE))
len = PAGE_SIZE - src_off;
and then we just truncate the data of the offending caller instead of
corrupting innocent data that happens to be adjacent. Although that's
not ideal either ... I dunno, what's the least bad poison to drink here?
next prev parent reply other threads:[~2020-12-07 23:40 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-07 22:57 [PATCH V2 0/2] " ira.weiny
2020-12-07 22:57 ` [PATCH V2 1/2] mm/highmem: Remove deprecated kmap_atomic ira.weiny
2020-12-07 22:57 ` [PATCH V2 2/2] mm/highmem: Lift memcpy_[to|from]_page to core ira.weiny
2020-12-07 23:26 ` Matthew Wilcox
2020-12-07 23:34 ` Dan Williams
2020-12-07 23:40 ` Matthew Wilcox [this message]
2020-12-07 23:49 ` Dan Williams
2020-12-08 21:32 ` Ira Weiny
2020-12-08 21:50 ` Matthew Wilcox
2020-12-08 22:23 ` Dan Williams
2020-12-08 22:32 ` Matthew Wilcox
2020-12-08 22:45 ` Darrick J. Wong
2020-12-08 22:54 ` Matthew Wilcox
2020-12-08 23:40 ` Dan Williams
2020-12-09 2:22 ` Ira Weiny
2020-12-09 4:03 ` Matthew Wilcox
2020-12-09 19:47 ` Dan Williams
2020-12-09 20:14 ` Matthew Wilcox
2020-12-09 20:19 ` Dan Williams
2020-12-10 5:35 ` Ira Weiny
2020-12-08 22:21 ` Dan Williams
2020-12-08 12:23 ` Matthew Wilcox
2020-12-08 16:38 ` Ira Weiny
2020-12-08 16:40 ` Matthew Wilcox
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