Re: [Qemu-arm] [PATCH 00/17] target/arm: Implement ARMv8.5-MemTag

[Peter Maydell]

On Mon, 14 Jan 2019 at 01:11, Richard Henderson
<address@hidden> wrote:
>
> Based-on: address@hidden
> aka the TBID patch set, which itself is based on the BTI patch set.
>
> The full tree is available at
>
>   https://github.org/rth7680/qemu.git tgt-arm-mte
>
> This extension isl also spelled MTE in the ARM.
>
> This patch set only attempts to implement linux-user emulation.
> For system emulation, I still miss the new cache flushing insns (easy)
> and the out-of-band physical memory for the allocation tags (harder).
>
> From a few mis-steps in writing the test cases for the extension,
> I might suggest that some future kernel's userland ABI for this have
> TCR.TCMA0 = 1, so that legacy code that is *not* MTE aware can use
> a frame pointer without accidentally tripping left over stack tags.
> (As seen in patch 5, SP+OFF is unchecked per the ISA but FP+OFF is not.)
>
> OTOH, depending on the application, that does make it easier for an
> attack vector to clean the tag off the top of a pointer to bypass
> store checking.  So, tricky.

I'm working through review of this, but feel free to rebase on
current master (which has now got a pile of your other patches
in it, since I've just merged target-arm.next) without waiting
for me to finish going through it.

thanks
-- PMM