arm64: hyp-stub: Forbid kprobing of the hyp-stub

BugLink: https://bugs.launchpad.net/bugs/1818803

commit 8fac5cbd upstream.

The hyp-stub is loaded by the kernel's early startup code at EL2
during boot, before KVM takes ownership later. The hyp-stub's
text is part of the regular kernel text, meaning it can be kprobed.

A breakpoint in the hyp-stub causes the CPU to spin in el2_sync_invalid.

Add it to the __hyp_text.
Signed-off-by: James Morse <james.morse@arm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

arch/arm64/kernel/hyp-stub.S

@@ -26,6 +26,8 @@
 #include <asm/virt.h>
 
 	.text
+	.pushsection	.hyp.text, "ax"
+
 	.align 11
 
 ENTRY(__hyp_stub_vectors)