From: Kees Cook <keescook@chromium.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-mm@kvack.org, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 3/3] mm/usercopy: Detect compound page overruns
Date: Tue, 5 Oct 2021 15:55:37 -0700 [thread overview]
Message-ID: <202110051555.72347C41@keescook> (raw)
In-Reply-To: <YVzN33mMLoWV136F@casper.infradead.org>
On Tue, Oct 05, 2021 at 11:12:47PM +0100, Matthew Wilcox wrote:
> On Tue, Oct 05, 2021 at 02:26:37PM -0700, Kees Cook wrote:
> > On Mon, Oct 04, 2021 at 11:42:23PM +0100, Matthew Wilcox (Oracle) wrote:
> > > + } else if (PageHead(page)) {
> > > + /* A compound allocation */
> > > + if (ptr + n > page_address(page) + page_size(page))
> > > + usercopy_abort("page alloc", NULL, to_user, 0, n);
> >
> > "0" could be "ptr - page_address(page)", I think? With that:
> >
> > Acked-by: Kees Cook <keescook@chromium.org>
>
> Right, so that can be:
>
> } else if (PageHead(page)) {
> /* A compound allocation */
> unsigned long offset = ptr - page_address(page);
> if (offset + n > page_size(page))
> usercopy_abort("page alloc", NULL, to_user, offset, n);
>
> which saves us calling page_address() twice. Probably GCC is smart
> enough to CSE it anyway, but it also avoids splitting at the 80 column
> boundary ;-)
Perfect, yes!
--
Kees Cook
next prev parent reply other threads:[~2021-10-05 22:55 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-04 22:42 [PATCH 0/3] Assorted improvements to usercopy Matthew Wilcox (Oracle)
2021-10-04 22:42 ` [PATCH 1/3] mm/usercopy: Check kmap addresses properly Matthew Wilcox (Oracle)
2021-10-05 21:23 ` Kees Cook
2021-10-05 21:43 ` Matthew Wilcox
2021-10-05 21:54 ` Kees Cook
2021-10-04 22:42 ` [PATCH 2/3] mm/usercopy: Detect vmalloc overruns Matthew Wilcox (Oracle)
2021-10-05 21:25 ` Kees Cook
2021-10-06 1:26 ` Matthew Wilcox
2021-10-06 3:02 ` Kees Cook
2021-10-04 22:42 ` [PATCH 3/3] mm/usercopy: Detect compound page overruns Matthew Wilcox (Oracle)
2021-10-05 21:26 ` Kees Cook
2021-10-05 22:12 ` Matthew Wilcox
2021-10-05 22:55 ` Kees Cook [this message]
2021-10-05 21:27 ` [PATCH 0/3] Assorted improvements to usercopy Kees Cook
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