[PATCH v8 0/4] arm64: Enable BTI for the executable as well as the interpreter

[Will Deacon]

On Mon, Jan 24, 2022 at 03:07:00PM +0000, Mark Brown wrote:
> Deployments of BTI on arm64 have run into issues interacting with
> systemd's MemoryDenyWriteExecute feature.  Currently for dynamically
> linked executables the kernel will only handle architecture specific
> properties like BTI for the interpreter, the expectation is that the
> interpreter will then handle any properties on the main executable.
> For BTI this means remapping the executable segments PROT_EXEC |
> PROT_BTI.
> 
> This interacts poorly with MemoryDenyWriteExecute since that is
> implemented using a seccomp filter which prevents setting PROT_EXEC on
> already mapped memory and lacks the context to be able to detect that
> memory is already mapped with PROT_EXEC.  This series resolves this by
> handling the BTI property for both the interpreter and the main
> executable.

This appears to be a user-visible change which cannot be detected or
disabled from userspace. If there is code out there which does not work
when BTI is enabled, won't that now explode when the kernel enables it?
How are we supposed to handle such a regression?

Will