[S390] Write protect module text and RO data

Implement write protection for kernel modules text and read-only
data sections by implementing set_memory_[ro|rw] on s390.
Since s390 has no execute bit in the pte's NX is not supported.

set_memory_[ro|rw] will only work on normal pages and not on
large pages, so in case a large page should be modified bail
out with a warning.

Signed-off-by: Jan Glauber <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

arch/s390/Kconfig.debug

···
 
 	  If unsure, or if you run an older (pre 4.4) gcc, say N.
 
+config DEBUG_SET_MODULE_RONX
+	def_bool y
+	depends on MODULES
 endmenu

arch/s390/include/asm/cacheflush.h

···
 void kernel_map_pages(struct page *page, int numpages, int enable);
 #endif
 
+int set_memory_ro(unsigned long addr, int numpages);
+int set_memory_rw(unsigned long addr, int numpages);
+int set_memory_nx(unsigned long addr, int numpages);
+
 #endif /* _S390_CACHEFLUSH_H */

arch/s390/mm/Makefile

···
 	    page-states.o gup.o
 obj-$(CONFIG_CMM) += cmm.o
 obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
+obj-$(CONFIG_DEBUG_SET_MODULE_RONX) += pageattr.o

arch/s390/mm/pageattr.c

···
+/*
+ * Copyright IBM Corp. 2011
+ * Author(s): Jan Glauber <[e-mail]>
+ */
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/hugetlb.h>
+#include <asm/pgtable.h>
+
+static void change_page_attr(unsigned long addr, int numpages,
+			     pte_t (*set) (pte_t))
+{
+	pte_t *ptep, pte;
+	pmd_t *pmdp;
+	pud_t *pudp;
+	pgd_t *pgdp;
+	int i;
+
+	for (i = 0; i < numpages; i++) {
+		pgdp = pgd_offset(&init_mm, addr);
+		pudp = pud_offset(pgdp, addr);
+		pmdp = pmd_offset(pudp, addr);
+		if (pmd_huge(*pmdp)) {
+			WARN_ON_ONCE(1);
+			continue;
+		}
+		ptep = pte_offset_kernel(pmdp, addr + i * PAGE_SIZE);
+
+		pte = *ptep;
+		pte = set(pte);
+		ptep_invalidate(&init_mm, addr + i * PAGE_SIZE, ptep);
+		*ptep = pte;
+	}
+}
+
+int set_memory_ro(unsigned long addr, int numpages)
+{
+	change_page_attr(addr, numpages, pte_wrprotect);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(set_memory_ro);
+
+int set_memory_rw(unsigned long addr, int numpages)
+{
+	change_page_attr(addr, numpages, pte_mkwrite);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(set_memory_rw);
+
+/* not possible */
+int set_memory_nx(unsigned long addr, int numpages)
+{
+	return 0;
+}
+EXPORT_SYMBOL_GPL(set_memory_nx);