KVM: arm64: Compute TPIDR_EL2 ignoring MTE tag

KASAN in HW_TAGS mode will store MTE tags in the top byte of the
pointer. When computing the offset for TPIDR_EL2 we don't want anything
in the top byte, so remove the tag to ensure the computation is correct
no matter what the tag.

Fixes: 94ab5b61 ("kasan, arm64: enable CONFIG_KASAN_HW_TAGS")
Signed-off-by: Steven Price <steven.price@arm.com>
[maz: added comment]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210108161254.53674-1-steven.price@arm.com

arch/arm64/kvm/arm.c

@@ -1396,8 +1396,9 @@ static void cpu_init_hyp_mode(void)
 	 * Calculate the raw per-cpu offset without a translation from the
 	 * kernel's mapping to the linear mapping, and store it in tpidr_el2
 	 * so that we can use adr_l to access per-cpu variables in EL2.
+	 * Also drop the KASAN tag which gets in the way...
 	 */
-	params->tpidr_el2 = (unsigned long)this_cpu_ptr_nvhe_sym(__per_cpu_start) -
+	params->tpidr_el2 = (unsigned long)kasan_reset_tag(this_cpu_ptr_nvhe_sym(__per_cpu_start)) -
 			    (unsigned long)kvm_ksym_ref(CHOOSE_NVHE_SYM(__per_cpu_start));
 
 	params->mair_el2 = read_sysreg(mair_el1);