target/arm: Get correct MMU index for other-security-state

target/arm: Get correct MMU index for other-security-state

In arm_v7m_mmu_idx_for_secstate() we get the 'priv' level to pass to
armv7m_mmu_idx_for_secstate_and_priv() by calling arm_current_el().
This is incorrect when the security state being queried is not the
current one, because arm_current_el() uses the current security state
to determine which of the banked CONTROL.nPRIV bits to look at.
The effect was that if (for instance) Secure state was in privileged
mode but Non-Secure was not then we would return the wrong MMU index.

The only places where we are using this function in a way that could
trigger this bug are for the stack loads during a v8M function-return
and for the instruction fetch of a v8M SG insn.

Fix the bug by expanding out the M-profile version of the
arm_current_el() logic inline so it can use the passed in secstate
rather than env->v7m.secure.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20201022164408.13214-1-peter.maydell@linaro.org