linux-kernel - Re: [PATCH] arch:arm:mm:Correction in the boundary check for module end address.

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Date:	Mon, 9 Nov 2015 16:01:37 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Jungseung Lee <js07.lee@...il.com>
Cc:	Shailendra Verma <shailendra.v@...ung.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	Riley Andrews <riandrews@...roid.com>,
	Laura Abbott <lauraa@...eaurora.org>,
	Shailendra Verma <shailendra.capricorn@...il.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Mitchel Humpherys <mitchelh@...eaurora.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Gioh Kim <gioh.kim@....com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Shawn Lin <shawn.lin@...k-chips.com>,
	Markus Elfring <elfring@...rs.sourceforge.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, devel@...verdev.osuosl.org,
	Ravikant Bijendra Sharma <ravikant.s2@...sung.com>,
	Shailendra Verma <shailendra.v@...sung.com>,
	linux-kernel@...r.kernel.org, vidushi.koul@...sung.com,
	hillf.zj@...baba-inc.com
Subject: Re: [PATCH] arch:arm:mm:Correction in the boundary check for module
 end address.

On Tue, Nov 10, 2015 at 12:35:50AM +0900, Jungseung Lee wrote:
> Hi,
> 
> 2015-11-09 16:57 GMT+09:00 Shailendra Verma <shailendra.v@...ung.com>:
> > From: Shailendra Verma <Shailendra.v@...sung.com>
> >
> > The module end boundary check is not proper.The out of bound value
> > of module end can produce undesired results.
> >
> > Signed-off-by: Shailendra Verma <Shailendra.v@...sung.com>
> > Reviewed-by: Ravikant Bijendra Sharma <ravikant.s2@...sung.com>
> > ---
> >  linux-4.3-rc6/arch/arm/mm/pageattr.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/linux-4.3-rc6/arch/arm/mm/pageattr.c b/linux-4.3-rc6/arch/arm/mm/pageattr.c
> > index cf30daf..be7fe4b 100644
> > --- a/linux-4.3-rc6/arch/arm/mm/pageattr.c
> > +++ b/linux-4.3-rc6/arch/arm/mm/pageattr.c
> > @@ -52,7 +52,7 @@ static int change_memory_common(unsigned long addr, int numpages,
> >         if (start < MODULES_VADDR || start >= MODULES_END)
> >                 return -EINVAL;
> >
> > -       if (end < MODULES_VADDR || start >= MODULES_END)
> > +       if (end < MODULES_VADDR || end >= MODULES_END)
> >                 return -EINVAL;
> >
> >         data.set_mask = set_mask;
> > --
> > 1.7.9.5
> >
> Same patch with proper format is already submitted by Hillf.
> https://lkml.org/lkml/2015/5/3/202

What happened to that patch?  It should at least have had a:

Fixes: f2ca09f381a5 ("ARM: 8311/1: Don't use is_module_addr in setting page attributes")

tag on it, and it needs to find its way into the patch system.  As
no one has reported a crash (I don't think it's crash-causing, but is
merely a correctness issue) I don't see any reason to backport it to
stable trees.

Other changes are needed here as well - the original commit creating
this contains:

+       if (!IS_ALIGNED(addr, PAGE_SIZE)) {
+               start &= PAGE_MASK;
+               end = start + size;
+               WARN_ON_ONCE(1);
+       }

which is truely amazing.  Fine, it may not be intended to work with
non-aligned addresses, but if we're going to round the start down,
then rounding the end down as well like that is also buggy.

	unsigned long start = addr;
	unsigned long size = PAGE_SIZE * numpages;
	unsigned long end = start + size;

	if (WARN_ON_ONCE(!IS_ALIGNED(addr, PAGE_SIZE)) {
		start &= PAGE_MASK;
		end = PAGE_ALIGN(end);
	}

would be much better - this will round 'end' up, so we encompass the
entire requested region.

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