On Fri, Aug 23, 2019 at 05:19:13PM +0100, Catalin Marinas wrote: > On Thu, Aug 22, 2019 at 05:37:23PM +0100, Dave P Martin wrote: > > On Thu, Aug 22, 2019 at 04:55:32PM +0100, Catalin Marinas wrote: > > > On Wed, Aug 21, 2019 at 07:46:51PM +0100, Dave P Martin wrote: [...] > > > > sigaltstack() is interesting, since we don't support tagged stacks. > > > > > > We should support tagged SP with the new ABI as they'll be required for > > > MTE. sigaltstack() and clone() are the two syscalls that come to mind > > > here. > > > > > > > Do we keep the ss_sp tag in the kernel, but squash it when delivering > > > > a signal to the alternate stack? > > > > > > We don't seem to be doing any untagging, so we just just use whatever > > > the caller asked for. We may need a small test to confirm. > > > > If we want to support tagged SP, then I guess we shouldn't be squashing > > the tag anywhere. A test for that would be sensible to have. > > I hacked the sas.c kselftest to use a tagged stack and works fine, the > SP register has a tagged address on the signal handler. Cool... [...] > > > > There is no foolproof rule, unless we can rewrite history... > > > > > > I would expect the norm to be the preservation of tags with a few > > > exceptions. The only ones I think where we won't preserve the tags are > > > mmap, mremap, brk (apart from the signal stuff already mentioned in the > > > current tagged-pointers.rst doc). > > > > > > So I can remove this paragraph altogether and add a note in part 3 of > > > the tagged-address-abi.rst document that mmap/mremap/brk do not preserve > > > the tag information. > > > > Deleting text is always a good idea ;) > > I'm going this route ;). [reply deleted] Cheers ---Dave
