On Thu, Aug 30, 2018 at 1:41 PM, Andrey Konovalov [off-list ref] wrote:

arm64 has a feature called Top Byte Ignore, which allows to embed pointer
tags into the top byte of each pointer. Userspace programs (such as
HWASan, a memory debugging tool [1]) might use this feature and pass
tagged user pointers to the kernel through syscalls or other interfaces.

This patch makes a few of the kernel interfaces accept tagged user
pointers. The kernel is already able to handle user faults with tagged
pointers and has the untagged_addr macro, which this patchset reuses.

Thanks!

[1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html

Changes in v6:
- Added annotations for user pointer casts found by sparse.

Hi Catalin,

I've added annotations for the user pointer casts pointed by the new
sparse flag -Wcast-from-as as you asked. I've used __force casts
instead of adding specialized macros.

There are also non annotated casts for other pointer types (iomem,
rcu) which are detected with the new flag, should I annotate those as
well?

I'm not sure though what value would that bring though, as there are
~3000 various sparse warnings produced with the default flags anyway.

WDYT?

Thanks!

[1] https://github.com/lucvoo/sparse-dev/commit/5f960cb10f56ec2017c128ef9d16060e0145f292