arm64: traps: correctly handle MRS/MSR with XZR

Currently we hand-roll XZR-safe register handling in
user_cache_maint_handler(), though we forget to do the same in
ctr_read_handler(), and may erroneously write back to the user SP rather
than XZR.

Use the new helpers to handle these cases correctly and consistently.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Fixes: 116c81f4 ("arm64: Work around systems with mismatched cache line sizes")
Cc: Andre Przywara <andre.przywara@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/traps.c

@@ -466,7 +466,7 @@ static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs)
 	int crm = (esr & ESR_ELx_SYS64_ISS_CRM_MASK) >> ESR_ELx_SYS64_ISS_CRM_SHIFT;
 	int ret = 0;
 
-	address = (rt == 31) ? 0 : regs->regs[rt];
+	address = pt_regs_read_reg(regs, rt);
 
 	switch (crm) {
 	case ESR_ELx_SYS64_ISS_CRM_DC_CVAU:	/* DC CVAU, gets promoted */
@@ -495,8 +495,10 @@ static void user_cache_maint_handler(unsigned int esr, struct pt_regs *regs)
 static void ctr_read_handler(unsigned int esr, struct pt_regs *regs)
 {
 	int rt = (esr & ESR_ELx_SYS64_ISS_RT_MASK) >> ESR_ELx_SYS64_ISS_RT_SHIFT;
+	unsigned long val = arm64_ftr_reg_user_value(&arm64_ftr_reg_ctrel0);
+
+	pt_regs_write_reg(regs, rt, val);
 
-	regs->regs[rt] = arm64_ftr_reg_user_value(&arm64_ftr_reg_ctrel0);
 	regs->pc += 4;
 }