We were incorrectly assuming that only the first byte of an MTE access
is checked against the tags. But per the ARM, unaligned accesses are
pre-decomposed into single-byte accesses. So by the time we reach the
actual MTE check in the ARM pseudocode, all accesses are aligned.
Therefore, the first failure is always either the first byte of the
access, or the first byte of the granule.
In addition, some of the arithmetic is off for last-first -> count.
This does not become directly visible until a later patch that passes
single bytes into this function, so ptr == ptr_last.
Buglink: https://bugs.launchpad.net/bugs/1921948
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210416183106.1516563-2-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: tweaked a comment]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
98f96050aa