On Wed, Oct 14, 2020 at 04:43:23PM -0700, Peter Collingbourne wrote: > On Fri, Sep 18, 2020 at 1:30 AM Will Deacon <will@xxxxxxxxxx> wrote: > > I think so, yes. I'm hoping to queue it for 5.10, once I have an Ack from > > the Android tools side on the per-thread ABI. > > Our main requirement on the Android side is to provide an API for > changing the tag checking mode in all threads in a process while > multiple threads are running. I think we've been able to accomplish > this [1] by using a libc private real-time signal which is sent to all > threads. The implementation has been tested on FVP via the included > unit tests. The code has also been tested on real hardware in a > multi-threaded app process (of course we don't have MTE-enabled > hardware, so the implementation was tested on hardware by hacking it > to disable the tagged address ABI instead of changing the tag checking > mode, and then verifying via ptrace(PTRACE_GETREGSET) that the tagged > address ABI was disabled in all threads). > > That being said, as with any code at the nexus of concurrency and > POSIX signals, the implementation is quite tricky so I would say it > falls more into the category of "no obvious problems" than "obviously > no problems". It also relies on changes to the implementations of > pthread APIs so it wouldn't catch threads created directly via clone() > rather than via pthread_create(). I think we would be able to ignore > such threads on Android without causing compatibility issues because > we can require the process to not create threads via clone() before > calling the function. I imagine this may not necessarily work for > other libcs like glibc, though, but as I understand it glibc has no > plan to offer such an API. > > I feel confident enough in the kernel API though that I think that > it's reasonable as a starting point at least, and that if a problem > with the API is discovered I would expect it to be fixable by adding > new APIs, so: > > Acked-by: Peter Collingbourne <pcc@xxxxxxxxxx> Thanks, Peter. This series has already landed upstream, so I'm unable to add your Ack now, but the text above is very helpful. Cheers, Will > [1] https://android-review.googlesource.com/c/platform/bionic/+/1427377
