On Thu, Sep 17, 2020 at 05:15:53PM +0100, Dave Martin wrote: > On Thu, Sep 17, 2020 at 10:02:30AM +0100, Catalin Marinas wrote: > > On Thu, Sep 17, 2020 at 09:11:08AM +0100, Will Deacon wrote: > > > On Fri, Sep 04, 2020 at 11:30:29AM +0100, Catalin Marinas wrote: > > > > From: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> > > > > > > > > Memory Tagging Extension (part of the ARMv8.5 Extensions) provides > > > > a mechanism to detect the sources of memory related errors which > > > > may be vulnerable to exploitation, including bounds violations, > > > > use-after-free, use-after-return, use-out-of-scope and use before > > > > initialization errors. > > > > > > > > Add Memory Tagging Extension documentation for the arm64 linux > > > > kernel support. > > > > > > > > Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> > > > > Co-developed-by: Catalin Marinas <catalin.marinas@xxxxxxx> > > > > Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx> > > > > Acked-by: Szabolcs Nagy <szabolcs.nagy@xxxxxxx> > > > > > > I'm taking this to mean that Szabolcs is happy with the proposed ABI -- > > > please shout if that's not the case! > > > > I think Szabolcs is still on holiday. To summarise the past threads, > > AFAICT he's happy with this per-thread control ABI but the discussion > > went on whether to expand it in the future (with a new bit) to > > synchronise the tag checking mode across all threads of a process. This > > adds some complications for the kernel as it needs an IPI to the other > > CPUs to set SCTLR_EL1 and it's also racy with multiple threads > > requesting different modes. > > > > Now, in the glibc land, if the tag check mode is controlled via > > environment variables, the dynamic loader can set this at process start > > while still in single-threaded mode and not touch it at run-time. The > > MTE checking can still be enabled at run-time, per mapped memory range > > via the PROT_MTE flag. This approach doesn't require any additional > > changes to the current patches. But it's for Szabolcs to confirm once > > he's back. > > > > > Wasn't there a man page kicking around too? Would be good to see that > > > go upstream (to the manpages project, of course). > > > > Dave started writing one for the tagged address ABI, not sure where that > > is. For the MTE additions, we are waiting for the ABI to be upstreamed. > > The tagged address ABI control stuff is upstream in the man-pages-5.08 > release. > > I don't think anyone drafted anything for MTE yet. Do we consider the > MTE ABI to be sufficiently stable now for it to be worth starting > drafting something? I think so, yes. I'm hoping to queue it for 5.10, once I have an Ack from the Android tools side on the per-thread ABI. Will
