powerpc: Fail ioremap() instead of silently ignoring flags when PAGE_USER is set

Calling ioremap() with _PAGE_USER (or _PAGE_PRIVILEDGE unset)
is wrong. Loudly fail the call to ioremap() instead of blindly
clearing the flags.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/b6dd5485ad00d2aafd2bb9b7c2c4eac3ebf2cdaf.1695659959.git.christophe.leroy@csgroup.eu

arch/powerpc/mm/ioremap.c

@@ -51,7 +51,8 @@ void __iomem *ioremap_prot(phys_addr_t addr, size_t size, unsigned long flags)
 		pte = pte_mkdirty(pte);
 
 	/* we don't want to let _PAGE_USER leak out */
-	pte = pte_mkprivileged(pte);
+	if (WARN_ON(pte_user(pte)))
+		return NULL;
 
 	if (iowa_is_active())
 		return iowa_ioremap(addr, size, pte_pgprot(pte), caller);