[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 <jang@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 56 insertions, 0 deletions

diff --git a/arch/s390/mm/Makefile b/arch/s390/mm/Makefile
index 6fbc6f3fbdf..d98fe9004a5 100644
--- a/arch/s390/mm/Makefile
+++ b/arch/s390/mm/Makefile
@@ -6,3 +6,4 @@ obj-y	 := init.o fault.o extmem.o mmap.o vmem.o pgtable.o maccess.o \
 	    page-states.o gup.o
 obj-$(CONFIG_CMM) += cmm.o
 obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
+obj-$(CONFIG_DEBUG_SET_MODULE_RONX) += pageattr.o
diff --git a/arch/s390/mm/pageattr.c b/arch/s390/mm/pageattr.c
new file mode 100644
index 00000000000..122ffbd08ce
--- /dev/null
+++ b/arch/s390/mm/pageattr.c
@@ -0,0 +1,55 @@
+/*
+ * Copyright IBM Corp. 2011
+ * Author(s): Jan Glauber <jang@linux.vnet.ibm.com>
+ */
+#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);