On Tue, Aug 04, 2020 at 08:34:42PM +0100, Kevin Brodsky wrote: > On 15/07/2020 18:08, Catalin Marinas wrote: > > By default, even if PROT_MTE is set on a memory range, there is no tag > > check fault reporting (SIGSEGV). Introduce a set of option to the > > exiting prctl(PR_SET_TAGGED_ADDR_CTRL) to allow user control of the tag > > check fault mode: > > > > PR_MTE_TCF_NONE - no reporting (default) > > PR_MTE_TCF_SYNC - synchronous tag check fault reporting > > PR_MTE_TCF_ASYNC - asynchronous tag check fault reporting > > > > These options translate into the corresponding SCTLR_EL1.TCF0 bitfield, > > context-switched by the kernel. Note that uaccess done by the kernel is > > not checked and cannot be configured by the user. > > The last sentence is outdated, it should probably say that uaccess is only > checked in in synchronous mode. Thanks, I forgot about the commit log. The documentation was updated to: **Note**: Kernel accesses to the user address space (e.g. ``read()`` system call) are not checked if the user thread tag checking mode is ``PR_MTE_TCF_NONE`` or ``PR_MTE_TCF_ASYNC``. If the tag checking mode is ``PR_MTE_TCF_SYNC``, the kernel makes a best effort to check its user address accesses, however it cannot always guarantee it. -- Catalin
