[PATCH v1 4/4] arm64/mte: Add userspace interface for enabling asymmetric mode

[Evgenii Stepanov]

On Thu, Jan 27, 2022 at 07:57:12PM +0000, Mark Brown wrote:
> Since there PR_MTE_TCF_ values are a bitmask (allowing the kernel to choose
> between the multiple modes) and there are no free bits adjacent to the
> existing PR_MTE_TCF_ bits the set of bits used to specify the mode becomes
> disjoint. Programs using the new interface should be aware of this and
> programs that do not use it will not see any change in behaviour.

Extending PR_MTE_TCF_MASK seems bad for backward compatibility. User
code may do "flags =& ~PR_MTE_TCF_MASK" to disable MTE; when compiled
against an old version of the header this would fail to remove the ASYMM
bit.