static_call: Fix the module key fixup

Provided the target address of a R_X86_64_PC32 relocation is aligned,
the low two bits should be invariant between the relative and absolute
value.

Turns out the address is not aligned and things go sideways, ensure we
transfer the bits in the absolute form when fixing up the key address.

Fixes: 73f44fe19d35 ("static_call: Allow module use without exposing static_call_key")
Reported-by: Steven Rostedt <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>
Tested-by: Steven Rostedt (VMware) <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

kernel/static_call.c

···
 	struct static_call_site *site;
 
 	for (site = start; site != stop; site++) {
-		unsigned long addr = (unsigned long)static_call_key(site);
+		unsigned long s_key = (long)site->key + (long)&site->key;
+		unsigned long addr = s_key & ~STATIC_CALL_SITE_FLAGS;
 		unsigned long key;
 
 		/*
···
 			return -EINVAL;
 		}
 
-		site->key = (key - (long)&site->key) |
-			    (site->key & STATIC_CALL_SITE_FLAGS);
+		key |= s_key & STATIC_CALL_SITE_FLAGS;
+		site->key = key - (long)&site->key;
 	}
 
 	return __static_call_init(mod, start, stop);