s390/mm,pageattr: add more page table walk sanity checks

The current page table walk code in pageattr.c only checks for large pages
while walking the kernel page table, but happily assumes that everything
else is just fine.
Add more checks so we never access invalid memory regions.

Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/mm/pageattr.c b/arch/s390/mm/pageattr.c
index 0f33bab3e98483d6ac5df2f430cfa868d82517b7..b56953dd95f82fdf1ff17e4c28b1c08f8d041e84 100644 (file)
--- a/arch/s390/mm/pageattr.c
+++ b/arch/s390/mm/pageattr.c
@@ -8,25 +8,38 @@
 #include <asm/cacheflush.h>
 #include <asm/pgtable.h>
 
+static pte_t *walk_page_table(unsigned long addr)
+{
+       pgd_t *pgdp;
+       pud_t *pudp;
+       pmd_t *pmdp;
+       pte_t *ptep;
+
+       pgdp = pgd_offset_k(addr);
+       if (pgd_none(*pgdp))
+               return NULL;
+       pudp = pud_offset(pgdp, addr);
+       if (pud_none(*pudp))
+               return NULL;
+       pmdp = pmd_offset(pudp, addr);
+       if (pmd_none(*pmdp) || pmd_large(*pmdp))
+               return NULL;
+       ptep = pte_offset_kernel(pmdp, addr);
+       if (pte_none(*ptep))
+               return NULL;
+       return ptep;
+}
+
 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_large(*pmdp)) {
-                       WARN_ON_ONCE(1);
-                       continue;
-               }
-               ptep = pte_offset_kernel(pmdp, addr);
-
+               ptep = walk_page_table(addr);
+               if (WARN_ON_ONCE(!ptep))
+                       break;
                pte = *ptep;
                pte = set(pte);
                __ptep_ipte(addr, ptep);