On Fri, Feb 22, 2019 at 11:55 PM Dave Hansen dave.hansen@intel.com wrote:
On 2/22/19 4:53 AM, Andrey Konovalov wrote:
The following testing approaches has been taken to find potential issues with user pointer untagging:
- Static testing (with sparse [3] and separately with a custom static analyzer based on Clang) to track casts of __user pointers to integer types to find places where untagging needs to be done.
First of all, it's really cool that you took this approach. Sounds like there was a lot of systematic work to fix up the sites in the existing codebase.
But, isn't this a _bit_ fragile going forward? Folks can't just "make sparse" to find issues with missing untags.
Yes, this static approach can only be used as a hint to find some places where untagging is needed, but certainly not all.
This seems like something where we would ideally add an __tagged annotation (or something) to the source tree and then have sparse rules that can look for missed untags.
This has been suggested before, search for __untagged here [1]. However there are many places in the kernel where a __user pointer is casted into unsigned long and passed further. I'm not sure if it's possible apply a __tagged/__untagged kind of attribute to non-pointer types, is it?