On Thu, Jun 28, 2018 at 03:48:59PM +0100, Catalin Marinas wrote:

On Thu, Jun 28, 2018 at 12:46:11PM +0200, Luc Van Oostenryck wrote:

quoted

On Thu, Jun 28, 2018 at 11:27:42AM +0100, Catalin Marinas wrote:

quoted

On Thu, Jun 28, 2018 at 08:17:59AM +0200, Luc Van Oostenryck wrote:

quoted

On Wed, Jun 27, 2018 at 06:17:58PM +0100, Catalin Marinas wrote:

quoted

sparse is indeed an option. The current implementation doesn't warn on
an explicit cast from (void __user *) to (unsigned long) since that's a
valid thing in the kernel. I couldn't figure out if there's any other
__attribute__ that could be used to warn of such conversion.

sparse doesn't have such attribute but would an new option that would warn
on such cast be a solution for your case?

I can't tell for sure whether such sparse option would be the full
solution but detecting explicit __user pointer casts to long is a good
starting point. So far this patchset pretty much relies on detecting
a syscall failure and trying to figure out why, patching the kernel. It
doesn't really scale.

OK, I'll add such an option this evening.

That's great, thanks. I think this should cover casting pointers to any
integer types, not just "unsigned long" (e.g. long long).

Yes, of course.
 

The only downside is that with this patchset the untagging can be done
after the conversion to ulong (get_user_pages()) as that's where the
problem was noticed. With a new sparse feature, we'd have to annotate
the conversion sites (not sure how many until we run the tool though).

I've done a lot of hacking on sparse and as such I run a lot of tests.
What I see with these tests is that a lot of annotations are wrong or
missing so I'm very reluctant to add another attribute. Even more so
one that would be only slightly different than an existing one. OTOH,
if it's something localized or a one-shot and there is a need, ...
why not?

What would you ideally need?

-- Luc
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