On Mon, Jul 16, 2018 at 01:25:59PM +0200, Andrey Konovalov wrote:
On Thu, Jun 28, 2018 at 9:30 PM, Andrey Konovalov andreyknvl@google.com wrote:
On Wed, Jun 27, 2018 at 5:05 PM, Andrey Konovalov andreyknvl@google.com wrote:
On Tue, Jun 26, 2018 at 7:29 PM, Catalin Marinas catalin.marinas@arm.com wrote:
While I support this work, as a maintainer I'd like to understand whether we'd be in a continuous chase of ABI breaks with every kernel release or we have a better way to identify potential issues. Is there any way to statically analyse conversions from __user ptr to long for example? Or, could we get the compiler to do this for us?
OK, got it, I'll try to figure out a way to find these conversions.
I've prototyped a checker on top of clang static analyzer (initially looked at sparse, but couldn't find any documentation or examples). The results are here [1], search for "warning: user pointer cast". Sharing in case anybody wants to take a look, will look at them myself tomorrow.
[1] https://gist.github.com/xairy/433edd5c86456a64026247cb2fef2115
So the checker reports ~100 different places where a __user pointer being casted. I've looked through them and found 3 places where we need to add untagging. Source code lines below come from 4.18-rc2+ (6f0d349d).
[...]
I'll add the 3 patches with fixes to v5 of this patchset.
Thanks for investigating. You can fix those three places in your code but I was rather looking for a way to check such casting in the future for newly added code. While for the khwasan we can assume it's a debug option, the tagged user pointers are ABI and we need to keep it stable.
We could we actually add some macros for explicit conversion between __user ptr and long and silence the warning there (I guess this would work better for sparse). We can then detect new ptr to long casts as they appear. I just hope that's not too intrusive.
(I haven't tried the sparse patch yet, hopefully sometime this week)