[PATCH v17 03/15] arm64: Introduce prctl() options to control the tagged user addresses ABI

[Catalin Marinas]

On Wed, Jun 12, 2019 at 01:43:20PM +0200, Andrey Konovalov wrote:
> From: Catalin Marinas <catalin.marinas at arm.com>
> 
> It is not desirable to relax the ABI to allow tagged user addresses into
> the kernel indiscriminately. This patch introduces a prctl() interface
> for enabling or disabling the tagged ABI with a global sysctl control
> for preventing applications from enabling the relaxed ABI (meant for
> testing user-space prctl() return error checking without reconfiguring
> the kernel). The ABI properties are inherited by threads of the same
> application and fork()'ed children but cleared on execve().
> 
> The PR_SET_TAGGED_ADDR_CTRL will be expanded in the future to handle
> MTE-specific settings like imprecise vs precise exceptions.
> 
> Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>

A question for the user-space folk: if an application opts in to this
ABI, would you want the sigcontext.fault_address and/or siginfo.si_addr
to contain the tag? We currently clear it early in the arm64 entry.S but
we could find a way to pass it down if needed.

-- 
Catalin