s390: add no-execute support

Bit 0x100 of a page table, segment table of region table entry
can be used to disallow code execution for the virtual addresses
associated with the entry.

There is one tricky bit, the system call to return from a signal
is part of the signal frame written to the user stack. With a
non-executable stack this would stop working. To avoid breaking
things the protection fault handler checks the opcode that caused
the fault for 0x0a77 (sys_sigreturn) and 0x0aad (sys_rt_sigreturn)
and injects a system call. This is preferable to the alternative
solution with a stub function in the vdso because it works for
vdso=off and statically linked binaries as well.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 32 insertions, 10 deletions

diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index 45becc8a44ec..253046344b3c 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -79,6 +79,7 @@ pte_t __ref *vmem_pte_alloc(void)
  */
 static int vmem_add_mem(unsigned long start, unsigned long size)
 {
+	unsigned long pgt_prot, sgt_prot, r3_prot;
 	unsigned long pages4k, pages1m, pages2g;
 	unsigned long end = start + size;
 	unsigned long address = start;
@@ -88,6 +89,14 @@ static int vmem_add_mem(unsigned long start, unsigned long size)
 	pte_t *pt_dir;
 	int ret = -ENOMEM;
 
+	pgt_prot = pgprot_val(PAGE_KERNEL);
+	sgt_prot = pgprot_val(SEGMENT_KERNEL);
+	r3_prot = pgprot_val(REGION3_KERNEL);
+	if (!MACHINE_HAS_NX) {
+		pgt_prot &= ~_PAGE_NOEXEC;
+		sgt_prot &= ~_SEGMENT_ENTRY_NOEXEC;
+		r3_prot &= ~_REGION_ENTRY_NOEXEC;
+	}
 	pages4k = pages1m = pages2g = 0;
 	while (address < end) {
 		pg_dir = pgd_offset_k(address);
@@ -101,7 +110,7 @@ static int vmem_add_mem(unsigned long start, unsigned long size)
 		if (MACHINE_HAS_EDAT2 && pud_none(*pu_dir) && address &&
 		    !(address & ~PUD_MASK) && (address + PUD_SIZE <= end) &&
 		     !debug_pagealloc_enabled()) {
-			pud_val(*pu_dir) = address | pgprot_val(REGION3_KERNEL);
+			pud_val(*pu_dir) = address | r3_prot;
 			address += PUD_SIZE;
 			pages2g++;
 			continue;
@@ -116,7 +125,7 @@ static int vmem_add_mem(unsigned long start, unsigned long size)
 		if (MACHINE_HAS_EDAT1 && pmd_none(*pm_dir) && address &&
 		    !(address & ~PMD_MASK) && (address + PMD_SIZE <= end) &&
 		    !debug_pagealloc_enabled()) {
-			pmd_val(*pm_dir) = address | pgprot_val(SEGMENT_KERNEL);
+			pmd_val(*pm_dir) = address | sgt_prot;
 			address += PMD_SIZE;
 			pages1m++;
 			continue;
@@ -129,7 +138,7 @@ static int vmem_add_mem(unsigned long start, unsigned long size)
 		}
 
 		pt_dir = pte_offset_kernel(pm_dir, address);
-		pte_val(*pt_dir) = address |  pgprot_val(PAGE_KERNEL);
+		pte_val(*pt_dir) = address | pgt_prot;
 		address += PAGE_SIZE;
 		pages4k++;
 	}
@@ -200,6 +209,7 @@ static void vmem_remove_range(unsigned long start, unsigned long size)
  */
 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
 {
+	unsigned long pgt_prot, sgt_prot;
 	unsigned long address = start;
 	pgd_t *pg_dir;
 	pud_t *pu_dir;
@@ -207,6 +217,12 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
 	pte_t *pt_dir;
 	int ret = -ENOMEM;
 
+	pgt_prot = pgprot_val(PAGE_KERNEL);
+	sgt_prot = pgprot_val(SEGMENT_KERNEL);
+	if (!MACHINE_HAS_NX) {
+		pgt_prot &= ~_PAGE_NOEXEC;
+		sgt_prot &= ~_SEGMENT_ENTRY_NOEXEC;
+	}
 	for (address = start; address < end;) {
 		pg_dir = pgd_offset_k(address);
 		if (pgd_none(*pg_dir)) {
@@ -238,8 +254,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
 				new_page = vmemmap_alloc_block(PMD_SIZE, node);
 				if (!new_page)
 					goto out;
-				pmd_val(*pm_dir) = __pa(new_page) |
-					_SEGMENT_ENTRY | _SEGMENT_ENTRY_LARGE;
+				pmd_val(*pm_dir) = __pa(new_page) | sgt_prot;
 				address = (address + PMD_SIZE) & PMD_MASK;
 				continue;
 			}
@@ -259,8 +274,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node)
 			new_page = vmemmap_alloc_block(PAGE_SIZE, node);
 			if (!new_page)
 				goto out;
-			pte_val(*pt_dir) =
-				__pa(new_page) | pgprot_val(PAGE_KERNEL);
+			pte_val(*pt_dir) = __pa(new_page) | pgt_prot;
 		}
 		address += PAGE_SIZE;
 	}
@@ -372,13 +386,21 @@ out:
  */
 void __init vmem_map_init(void)
 {
-	unsigned long size = _eshared - _stext;
 	struct memblock_region *reg;
 
 	for_each_memblock(memory, reg)
 		vmem_add_mem(reg->base, reg->size);
-	set_memory_ro((unsigned long)_stext, size >> PAGE_SHIFT);
-	pr_info("Write protected kernel read-only data: %luk\n", size >> 10);
+	__set_memory((unsigned long) _stext,
+		     (_etext - _stext) >> PAGE_SHIFT,
+		     SET_MEMORY_RO | SET_MEMORY_X);
+	__set_memory((unsigned long) _etext,
+		     (_eshared - _etext) >> PAGE_SHIFT,
+		     SET_MEMORY_RO);
+	__set_memory((unsigned long) _sinittext,
+		     (_einittext - _sinittext) >> PAGE_SHIFT,
+		     SET_MEMORY_RO | SET_MEMORY_X);
+	pr_info("Write protected kernel read-only data: %luk\n",
+		(_eshared - _stext) >> 10);
 }
 
 /*