On Thu, Jun 13, 2019 at 02:23:43PM +0100, Dave P Martin wrote: > On Thu, Jun 13, 2019 at 01:28:21PM +0100, Catalin Marinas wrote: > > On Thu, Jun 13, 2019 at 12:37:32PM +0100, Dave P Martin wrote: > > > On Thu, Jun 13, 2019 at 11:15:34AM +0100, Vincenzo Frascino wrote: > > > > On 12/06/2019 16:35, Catalin Marinas wrote: > > > > > On Wed, Jun 12, 2019 at 03:21:10PM +0100, Vincenzo Frascino wrote: > > > > >> + - PR_GET_TAGGED_ADDR_CTRL: can be used to check the status of the Tagged > > > > >> + Address ABI. > > [...] > > > Is there a canonical way to detect whether this whole API/ABI is > > > available? (i.e., try to call this prctl / check for an HWCAP bit, > > > etc.) > > > > The canonical way is a prctl() call. HWCAP doesn't make sense since it's > > not a hardware feature. If you really want a different way of detecting > > this (which I don't think it's worth), we can reinstate the AT_FLAGS > > bit. > > Sure, I think this probably makes sense -- I'm still getting my around > which parts of the design are directly related to MTE and which aren't. > > I was a bit concerned about the interaction between > PR_SET_TAGGED_ADDR_CTRL and the sysctl: the caller might conclude that > this API is unavailable when actually tagged addresses are stuck on. > > I'm not sure whether this matters, but it's a bit weird. > > One option would be to change the semantics, so that the sysctl just > forbids turning tagging from off to on. Alternatively, we could return > a different error code to distinguish this case. This is the intention, just to forbid turning tagging on. We could return -EPERM instead, though my original intent was to simply pretend that the prctl does not exist like in an older kernel version. -- Catalin
