[S390] Remove data execution protection

The noexec support on s390 does not rely on a bit in the page table
entry but utilizes the secondary space mode to distinguish between
memory accesses for instructions vs. data. The noexec code relies
on the assumption that the cpu will always use the secondary space
page table for data accesses while it is running in the secondary
space mode. Up to the z9-109 class machines this has been the case.
Unfortunately this is not true anymore with z10 and later machines.
The load-relative-long instructions lrl, lgrl and lgfrl access the
memory operand using the same addressing-space mode that has been
used to fetch the instruction.
This breaks the noexec mode for all user space binaries compiled
with march=z10 or later. The only option is to remove the current
noexec support.

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

1 files changed, 11 insertions, 64 deletions

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 02ace3491c5..763620ec792 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -256,8 +256,6 @@ extern unsigned long VMALLOC_START;
 #define _PAGE_TYPE_FILE		0x601	/* bit 0x002 is used for offset !! */
 #define _PAGE_TYPE_RO		0x200
 #define _PAGE_TYPE_RW		0x000
-#define _PAGE_TYPE_EX_RO	0x202
-#define _PAGE_TYPE_EX_RW	0x002
 
 /*
  * Only four types for huge pages, using the invalid bit and protection bit
@@ -287,8 +285,6 @@ extern unsigned long VMALLOC_START;
  * _PAGE_TYPE_FILE	11?1   ->   11?1
  * _PAGE_TYPE_RO	0100   ->   1100
  * _PAGE_TYPE_RW	0000   ->   1000
- * _PAGE_TYPE_EX_RO	0110   ->   1110
- * _PAGE_TYPE_EX_RW	0010   ->   1010
  *
  * pte_none is true for bits combinations 1000, 1010, 1100, 1110
  * pte_present is true for bits combinations 0000, 0010, 0100, 0110, 1001
@@ -387,55 +383,33 @@ extern unsigned long VMALLOC_START;
 #define PAGE_NONE	__pgprot(_PAGE_TYPE_NONE)
 #define PAGE_RO		__pgprot(_PAGE_TYPE_RO)
 #define PAGE_RW		__pgprot(_PAGE_TYPE_RW)
-#define PAGE_EX_RO	__pgprot(_PAGE_TYPE_EX_RO)
-#define PAGE_EX_RW	__pgprot(_PAGE_TYPE_EX_RW)
 
 #define PAGE_KERNEL	PAGE_RW
 #define PAGE_COPY	PAGE_RO
 
 /*
- * Dependent on the EXEC_PROTECT option s390 can do execute protection.
- * Write permission always implies read permission. In theory with a
- * primary/secondary page table execute only can be implemented but
- * it would cost an additional bit in the pte to distinguish all the
- * different pte types. To avoid that execute permission currently
- * implies read permission as well.
+ * On s390 the page table entry has an invalid bit and a read-only bit.
+ * Read permission implies execute permission and write permission
+ * implies read permission.
  */
          /*xwr*/
 #define __P000	PAGE_NONE
 #define __P001	PAGE_RO
 #define __P010	PAGE_RO
 #define __P011	PAGE_RO
-#define __P100	PAGE_EX_RO
-#define __P101	PAGE_EX_RO
-#define __P110	PAGE_EX_RO
-#define __P111	PAGE_EX_RO
+#define __P100	PAGE_RO
+#define __P101	PAGE_RO
+#define __P110	PAGE_RO
+#define __P111	PAGE_RO
 
 #define __S000	PAGE_NONE
 #define __S001	PAGE_RO
 #define __S010	PAGE_RW
 #define __S011	PAGE_RW
-#define __S100	PAGE_EX_RO
-#define __S101	PAGE_EX_RO
-#define __S110	PAGE_EX_RW
-#define __S111	PAGE_EX_RW
-
-#ifndef __s390x__
-# define PxD_SHADOW_SHIFT	1
-#else /* __s390x__ */
-# define PxD_SHADOW_SHIFT	2
-#endif /* __s390x__ */
-
-static inline void *get_shadow_table(void *table)
-{
-	unsigned long addr, offset;
-	struct page *page;
-
-	addr = (unsigned long) table;
-	offset = addr & ((PAGE_SIZE << PxD_SHADOW_SHIFT) - 1);
-	page = virt_to_page((void *)(addr ^ offset));
-	return (void *)(addr_t)(page->index ? (page->index | offset) : 0UL);
-}
+#define __S100	PAGE_RO
+#define __S101	PAGE_RO
+#define __S110	PAGE_RW
+#define __S111	PAGE_RW
 
 /*
  * Certain architectures need to do special things when PTEs
@@ -446,14 +420,6 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
 			      pte_t *ptep, pte_t entry)
 {
 	*ptep = entry;
-	if (mm->context.noexec) {
-		if (!(pte_val(entry) & _PAGE_INVALID) &&
-		    (pte_val(entry) & _PAGE_SWX))
-			pte_val(entry) |= _PAGE_RO;
-		else
-			pte_val(entry) = _PAGE_TYPE_EMPTY;
-		ptep[PTRS_PER_PTE] = entry;
-	}
 }
 
 /*
@@ -662,11 +628,7 @@ static inline void pgd_clear_kernel(pgd_t * pgd)
 
 static inline void pgd_clear(pgd_t * pgd)
 {
-	pgd_t *shadow = get_shadow_table(pgd);
-
 	pgd_clear_kernel(pgd);
-	if (shadow)
-		pgd_clear_kernel(shadow);
 }
 
 static inline void pud_clear_kernel(pud_t *pud)
@@ -677,13 +639,8 @@ static inline void pud_clear_kernel(pud_t *pud)
 
 static inline void pud_clear(pud_t *pud)
 {
-	pud_t *shadow = get_shadow_table(pud);
-
 	pud_clear_kernel(pud);
-	if (shadow)
-		pud_clear_kernel(shadow);
 }
-
 #endif /* __s390x__ */
 
 static inline void pmd_clear_kernel(pmd_t * pmdp)
@@ -693,18 +650,12 @@ static inline void pmd_clear_kernel(pmd_t * pmdp)
 
 static inline void pmd_clear(pmd_t *pmd)
 {
-	pmd_t *shadow = get_shadow_table(pmd);
-
 	pmd_clear_kernel(pmd);
-	if (shadow)
-		pmd_clear_kernel(shadow);
 }
 
 static inline void pte_clear(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
 {
 	pte_val(*ptep) = _PAGE_TYPE_EMPTY;
-	if (mm->context.noexec)
-		pte_val(ptep[PTRS_PER_PTE]) = _PAGE_TYPE_EMPTY;
 }
 
 /*
@@ -903,10 +854,6 @@ static inline void ptep_invalidate(struct mm_struct *mm,
 	}
 	__ptep_ipte(address, ptep);
 	pte_val(*ptep) = _PAGE_TYPE_EMPTY;
-	if (mm->context.noexec) {
-		__ptep_ipte(address, ptep + PTRS_PER_PTE);
-		pte_val(*(ptep + PTRS_PER_PTE)) = _PAGE_TYPE_EMPTY;
-	}
 }
 
 /*