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From: Matthew Wilcox <willy@infradead.org>
To: Kees Cook <keescook@chromium.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 23:12:47 +0100	[thread overview]
Message-ID: <YVzN33mMLoWV136F@casper.infradead.org> (raw)
In-Reply-To: <202110051425.ABFA413@keescook>

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 ;-)


  reply	other threads:[~2021-10-05 22:13 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 [this message]
2021-10-05 22:55       ` Kees Cook
2021-10-05 21:27 ` [PATCH 0/3] Assorted improvements to usercopy Kees Cook

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