On Thu, Jun 13, 2019 at 04:45:54PM +0100, Vincenzo Frascino wrote:
On 13/06/2019 16:35, Catalin Marinas wrote:
On Thu, Jun 13, 2019 at 12:16:59PM +0100, Dave P Martin wrote:
On Wed, Jun 12, 2019 at 01:43:20PM +0200, Andrey Konovalov wrote:
+/*
- Control the relaxed ABI allowing tagged user addresses into the kernel.
- */
+static unsigned int tagged_addr_prctl_allowed = 1;
+long set_tagged_addr_ctrl(unsigned long arg) +{
- if (!tagged_addr_prctl_allowed)
return -EINVAL;So, tagging can actually be locked on by having a process enable it and then some possibly unrelated process clearing tagged_addr_prctl_allowed. That feels a bit weird.
The problem is that if you disable the ABI globally, lots of applications would crash. This sysctl is meant as a way to disable the opt-in to the TBI ABI. Another option would be a kernel command line option (I'm not keen on a Kconfig option).
Why you are not keen on a Kconfig option?
Because I don't want to rebuild the kernel/reboot just to be able to test how user space handles the ABI opt-in. I'm ok with a Kconfig option to disable this globally in addition to a run-time option (if actually needed, I'm not sure).