On Mon, May 18, 2020 at 02:12:24PM -0300, Luis Machado wrote: > On 5/18/20 1:47 PM, Dave Martin wrote: > > Wrinkle: just because MTE is "off", pages might still be mapped with > > PROT_MTE and have arbitrary tags set on them, and the debugger perhaps > > needs a way to know that. Currently grubbing around in /proc is the > > only way to discover that. Dunno whether it matters. > > That is the sort of thing that may confused the debugger. > > If MTE is "off" (and thus the debugger doesn't need to validate tags), then > the pages mapped with PROT_MTE that show up in /proc/<pid>/smaps should be > ignored? There is no such thing as global MTE "off". If the HWCAP is present, a user program can map an address with PROT_MTE and access tags. Maybe it uses it for extra storage, you never know, doesn't have to be heap allocation related. > I'm looking for a precise way to tell if MTE is being used or not for a > particular process/thread. This, in turn, will tell debuggers when to look > for PROT_MTE mappings in /proc/<pid>/smaps and when to validate tagged > addresses. > > So far my assumption was that MTE will always be "on" when HWCAP2_MTE is > present. So having HWCAP2_MTE means we have the NT_ARM_MTE regset and that > PROT_MTE pages have to be checked. Yes. I haven't figured out what to put in the regset yet, most likely the prctl value as it has other software-only controls like the tagged address ABI. -- Catalin
