On Mon, Jun 17, 2019 at 09:57:36AM -0700, Evgenii Stepanov wrote: > On Mon, Jun 17, 2019 at 6:56 AM Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > > On Wed, Jun 12, 2019 at 01:43:20PM +0200, Andrey Konovalov wrote: > > > From: Catalin Marinas <catalin.marinas@xxxxxxx> > > > > > > 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@xxxxxxx> > > > > 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. > > For HWASan this would not be useful because we instrument memory > accesses with explicit checks anyway. For MTE, on the other hand, it > would be very convenient to know the fault address tag without > disassembling the code. I could as this differently: does anything break if, once the user opts in to TBI, fault_address and/or si_addr have non-zero top byte? Alternatively, we could present the original FAR_EL1 register as a separate field as we do with ESR_EL1, independently of whether the user opted in to TBI or not. -- Catalin
