linux-kernel - Re: Acpi deadlocks with 3.7.0-rc4

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Date:	Wed, 28 Nov 2012 21:05:06 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	linux-acpi@...r.kernel.org
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Zdenek Kabelac <zkabelac@...hat.com>,
	Len Brown <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Acpi deadlocks with 3.7.0-rc4

On Wednesday, November 28, 2012 11:07:32 AM Linus Torvalds wrote:
> On Wed, Nov 28, 2012 at 9:27 AM, Zdenek Kabelac <zkabelac@...hat.com> wrote:
> >
> > I've attached bigger disasfun script output to BZ 51071.
> > https://bugzilla.kernel.org/show_bug.cgi?id=51071#c1
> >
> >
> >         if (ACPI_GET_DESCRIPTOR_TYPE(prefix_node) !=
> > 00000000000000a1 <acpi_ns_lookup+0xa1> cmpb   $0xf,0x8(%rbx)
> > 00000000000000a5 <acpi_ns_lookup+0xa5> je   0da  <acpi_ns_lookup+0xda>
> >
> > seems to be going out of bounds.
> 
> The whole "prefix_node" pointer is bogus. It seems to have the value 0x1000.
> 
> I wonder how that happened. It's loaded from 'scope_info->scope.node',
> and it *should* be a valid pointer.

Well, suppose that pnpacpi_build_resource_template() passes a handle that's
not a valid pointer to acpi_walk_resources().  What happens then is that
it is passed directly to acpi_rs_get_method_data() and from there to
acpi_ut_evaluate_object() - without validation (acpi_rs_get_method_data()
even has a comment about the parameters validity guaranteed by the caller,
heh, heh).  Then it becomes the prefix_node and is written into
info->prefix_node.  acpi_ns_evaluate() takes that and passes it to
acpi_ns_get_node() along with info->pathname that is just the name of the
method to evaluate, which is a valid string, so the "if (!pathname)" block in
acpi_ns_get_node() is not executed and we get scope_info.scope.node = prefix_node,
which is our bad pointer.  A pointer to that scope_info is passed to
acpi_ns_lookup() and we get the above.

So the code in pnpacpi_build_resource_template() is at fault by passing a
wrong pointer to acpi_walk_resources().  And the pointer is wrong probably
because the struct acpi_device pointed to by dev->data in there has been
removed during a previous suspend or resume (I'm not sure which one does
that), but the PNP layer has no idea about that.  And that bug has been there
for quite a while (like forever?).

Thanks,
Rafael

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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