[PATCH v7 18/29] arm64: mte: Allow user control of the tag check mode via prctl()

[Catalin Marinas]

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 The last sentence is outdated, it should probably say that uaccess is only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