arm64: treat unhandled compat el0 traps as undef

Currently, if a compat process reads or writes from/to a disabled
cp15/cp14 register, the trap is not handled by the el0_sync_compat
handler, and the kernel will head to bad_mode, where it will die(), and
oops(). For 64 bit processes, disabled system register accesses are
currently treated as unhandled instructions.

This patch modifies entry.S to treat these unhandled traps as undefined
instructions, sending a SIGILL to userspace. This gives processes a
chance to handle this and stop using inaccessible registers, and
prevents further issues in the kernel as a result of the die().
Reported-by: Johannes Jensen <Johannes.Jensen@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/entry.S

@@ -390,6 +390,16 @@ el0_sync_compat:
 	b.eq	el0_fpsimd_exc
 	cmp	x24, #ESR_EL1_EC_UNKNOWN	// unknown exception in EL0
 	b.eq	el0_undef
+	cmp	x24, #ESR_EL1_EC_CP15_32	// CP15 MRC/MCR trap
+	b.eq	el0_undef
+	cmp	x24, #ESR_EL1_EC_CP15_64	// CP15 MRRC/MCRR trap
+	b.eq	el0_undef
+	cmp	x24, #ESR_EL1_EC_CP14_MR	// CP14 MRC/MCR trap
+	b.eq	el0_undef
+	cmp	x24, #ESR_EL1_EC_CP14_LS	// CP14 LDC/STC trap
+	b.eq	el0_undef
+	cmp	x24, #ESR_EL1_EC_CP14_64	// CP14 MRRC/MCRR trap
+	b.eq	el0_undef
 	cmp	x24, #ESR_EL1_EC_BREAKPT_EL0	// debug exception in EL0
 	b.ge	el0_dbg
 	b	el0_inv