[PATCH 4/6] mm, arm64: untag user addresses in mm/gup.c

On Thu, May 03, 2018 at 04:09:56PM +0200, Andrey Konovalov wrote:

On Wed, May 2, 2018 at 7:25 PM, Andrey Konovalov [off-list ref] wrote:

quoted

On Wed, May 2, 2018 at 5:36 PM, Kirill A. Shutemov
[off-list ref] wrote:

quoted

On Wed, May 02, 2018 at 02:38:42PM +0000, Andrey Konovalov wrote:

quoted

quoted

Does having a tagged address here makes any difference? I couldn't hit a
failure with my simple tests (LD_PRELOAD a library that randomly adds
tags to pointers returned by malloc).

I think you're right, follow_page_mask is only called from
__get_user_pages, which already untagged the address. I'll remove
untagging here.

It also called from follow_page(). Have you covered all its callers?

Oh, missed that, will take a look.

I wasn't able to find anything that calls follow_page with pointers
passed from userspace except for the memory subsystem syscalls, and we
deliberately don't add untagging in those.

I guess I missed this part, but could you elaborate on this? Why?
Not yet or not ever?

Also I wounder if we can find (with sparse?) all places where we cast out
__user. This would give a nice list of places where to pay attention.

-- 
 Kirill A. Shutemov