[PATCH v17 0/3] arm64: expose FAR_EL1 tag bits in siginfo

[Eric W. Biederman]

Peter Collingbourne <pcc at google.com> writes:

> The kernel currently clears the tag bits (i.e. bits 56-63) in the fault
> address exposed via siginfo.si_addr and sigcontext.fault_address. However,
> the tag bits may be needed by tools in order to accurately diagnose
> memory errors, such as HWASan [1] or future tools based on the Memory
> Tagging Extension (MTE).
>
> We should not stop clearing these bits in the existing fault address
> fields, because there may be existing userspace applications that are
> expecting the tag bits to be cleared. Instead, introduce a flag in
> sigaction.sa_flags, SA_EXPOSE_TAGBITS, and only expose the tag bits
> there if the signal handler has this flag set.
>
> In order to allow userspace to determine whether SA_EXPOSE_TAGBITS
> is supported, we first introduce a mechanism for userspace to detect
> kernel support for SA_* flags.
>
> These patches need to be applied on top of:
> https://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git signal-for-v5.11

The first two patches look good and I have applied them.

While I was at it I added Link tags to the LKML postings to the entire
series.  I don't think anyone has merged my branch into another so it
should still be safe.

Eric