powerpc/mm: add exec protection on powerpc 603

The 603 doesn't have a HASH table, TLB misses are handled by
software. It is then possible to generate page fault when
_PAGE_EXEC is not set like in nohash/32.

There is one "reserved" PTE bit available, this patch uses
it for _PAGE_EXEC.

In order to support it, set_pte_filter() and
set_access_flags_filter() are made common, and the handling
is made dependent on MMU_FTR_HPTE_TABLE

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Author: chleroy

arch/powerpc/include/asm/book3s/32/hash.h

@@ -26,6 +26,7 @@
 #define _PAGE_WRITETHRU	0x040	/* W: cache write-through */
 #define _PAGE_DIRTY	0x080	/* C: page changed */
 #define _PAGE_ACCESSED	0x100	/* R: page referenced */
+#define _PAGE_EXEC	0x200	/* software: exec allowed */
 #define _PAGE_RW	0x400	/* software: user write access allowed */
 #define _PAGE_SPECIAL	0x800	/* software: Special page */
 

arch/powerpc/include/asm/book3s/32/pgtable.h

@@ -10,9 +10,9 @@
 /* And here we include common definitions */
 
 #define _PAGE_KERNEL_RO		0
-#define _PAGE_KERNEL_ROX	0
+#define _PAGE_KERNEL_ROX	(_PAGE_EXEC)
 #define _PAGE_KERNEL_RW		(_PAGE_DIRTY | _PAGE_RW)
-#define _PAGE_KERNEL_RWX	(_PAGE_DIRTY | _PAGE_RW)
+#define _PAGE_KERNEL_RWX	(_PAGE_DIRTY | _PAGE_RW | _PAGE_EXEC)
 
 #define _PAGE_HPTEFLAGS _PAGE_HASHPTE
 
@@ -66,11 +66,11 @@ static inline bool pte_user(pte_t pte)
  */
 #define PAGE_NONE	__pgprot(_PAGE_BASE)
 #define PAGE_SHARED	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_RW)
-#define PAGE_SHARED_X	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_RW)
+#define PAGE_SHARED_X	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_RW | _PAGE_EXEC)
 #define PAGE_COPY	__pgprot(_PAGE_BASE | _PAGE_USER)
-#define PAGE_COPY_X	__pgprot(_PAGE_BASE | _PAGE_USER)
+#define PAGE_COPY_X	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_EXEC)
 #define PAGE_READONLY	__pgprot(_PAGE_BASE | _PAGE_USER)
-#define PAGE_READONLY_X	__pgprot(_PAGE_BASE | _PAGE_USER)
+#define PAGE_READONLY_X	__pgprot(_PAGE_BASE | _PAGE_USER | _PAGE_EXEC)
 
 /* Permission masks used for kernel mappings */
 #define PAGE_KERNEL	__pgprot(_PAGE_BASE | _PAGE_KERNEL_RW)
@@ -318,7 +318,7 @@ static inline void __ptep_set_access_flags(struct vm_area_struct *vma,
 					   int psize)
 {
 	unsigned long set = pte_val(entry) &
-		(_PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_RW);
+		(_PAGE_DIRTY | _PAGE_ACCESSED | _PAGE_RW | _PAGE_EXEC);
 
 	pte_update(ptep, 0, set);
 
@@ -371,7 +371,7 @@ static inline int pte_dirty(pte_t pte)		{ return !!(pte_val(pte) & _PAGE_DIRTY);
 static inline int pte_young(pte_t pte)		{ return !!(pte_val(pte) & _PAGE_ACCESSED); }
 static inline int pte_special(pte_t pte)	{ return !!(pte_val(pte) & _PAGE_SPECIAL); }
 static inline int pte_none(pte_t pte)		{ return (pte_val(pte) & ~_PTE_NONE_MASK) == 0; }
-static inline bool pte_exec(pte_t pte)		{ return true; }
+static inline bool pte_exec(pte_t pte)		{ return pte_val(pte) & _PAGE_EXEC; }
 
 static inline int pte_present(pte_t pte)
 {
@@ -438,7 +438,7 @@ static inline pte_t pte_wrprotect(pte_t pte)
 
 static inline pte_t pte_exprotect(pte_t pte)
 {
-	return pte;
+	return __pte(pte_val(pte) & ~_PAGE_EXEC);
 }
 
 static inline pte_t pte_mkclean(pte_t pte)
@@ -453,7 +453,7 @@ static inline pte_t pte_mkold(pte_t pte)
 
 static inline pte_t pte_mkexec(pte_t pte)
 {
-	return pte;
+	return __pte(pte_val(pte) | _PAGE_EXEC);
 }
 
 static inline pte_t pte_mkpte(pte_t pte)

arch/powerpc/include/asm/cputable.h

@@ -296,7 +296,7 @@ static inline void cpu_feature_keys_init(void) { }
 #define CPU_FTRS_PPC601	(CPU_FTR_COMMON | CPU_FTR_601 | \
 	CPU_FTR_COHERENT_ICACHE | CPU_FTR_UNIFIED_ID_CACHE | CPU_FTR_USE_RTC)
 #define CPU_FTRS_603	(CPU_FTR_COMMON | CPU_FTR_MAYBE_CAN_DOZE | \
-	    CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_PPC_LE)
+	    CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_PPC_LE | CPU_FTR_NOEXECUTE)
 #define CPU_FTRS_604	(CPU_FTR_COMMON | CPU_FTR_PPC_LE)
 #define CPU_FTRS_740_NOTAU	(CPU_FTR_COMMON | \
 	    CPU_FTR_MAYBE_CAN_DOZE | CPU_FTR_L2CR | \
@@ -367,15 +367,15 @@ static inline void cpu_feature_keys_init(void) { }
 	    CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_L2CR | CPU_FTR_ALTIVEC_COMP | \
 	    CPU_FTR_SPEC7450 | CPU_FTR_NAP_DISABLE_L2_PR | \
 	    CPU_FTR_PPC_LE | CPU_FTR_NEED_PAIRED_STWCX)
-#define CPU_FTRS_82XX	(CPU_FTR_COMMON | CPU_FTR_MAYBE_CAN_DOZE)
+#define CPU_FTRS_82XX	(CPU_FTR_COMMON | CPU_FTR_MAYBE_CAN_DOZE | CPU_FTR_NOEXECUTE)
 #define CPU_FTRS_G2_LE	(CPU_FTR_COMMON | CPU_FTR_MAYBE_CAN_DOZE | \
 	    CPU_FTR_MAYBE_CAN_NAP)
 #define CPU_FTRS_E300	(CPU_FTR_MAYBE_CAN_DOZE | \
 	    CPU_FTR_MAYBE_CAN_NAP | \
-	    CPU_FTR_COMMON)
+	    CPU_FTR_COMMON  | CPU_FTR_NOEXECUTE)
 #define CPU_FTRS_E300C2	(CPU_FTR_MAYBE_CAN_DOZE | \
 	    CPU_FTR_MAYBE_CAN_NAP | \
-	    CPU_FTR_COMMON | CPU_FTR_FPU_UNAVAILABLE)
+	    CPU_FTR_COMMON | CPU_FTR_FPU_UNAVAILABLE  | CPU_FTR_NOEXECUTE)
 #define CPU_FTRS_CLASSIC32	(CPU_FTR_COMMON)
 #define CPU_FTRS_8XX	(CPU_FTR_NOEXECUTE)
 #define CPU_FTRS_40X	(CPU_FTR_NODSISRALIGN | CPU_FTR_NOEXECUTE)

arch/powerpc/kernel/head_32.S

@@ -503,7 +503,7 @@ InstructionTLBMiss:
 	lis	r1,PAGE_OFFSET@h		/* check if kernel address */
 	cmplw	0,r1,r3
 	mfspr	r2,SPRN_SPRG_THREAD
-	li	r1,_PAGE_USER|_PAGE_PRESENT /* low addresses tested as user */
+	li	r1,_PAGE_USER|_PAGE_PRESENT|_PAGE_EXEC /* low addresses tested as user */
 	lwz	r2,PGDIR(r2)
 	bge-	112f
 	mfspr	r2,SPRN_SRR1		/* and MSR_PR bit from SRR1 */

arch/powerpc/mm/dump_linuxpagetables-generic.c

@@ -21,13 +21,11 @@ static const struct flag_info flag_array[] = {
 		.set	= "rw",
 		.clear	= "r ",
 	}, {
-#ifndef CONFIG_PPC_BOOK3S_32
 		.mask	= _PAGE_EXEC,
 		.val	= _PAGE_EXEC,
 		.set	= " X ",
 		.clear	= "   ",
 	}, {
-#endif
 		.mask	= _PAGE_PRESENT,
 		.val	= _PAGE_PRESENT,
 		.set	= "present",

arch/powerpc/mm/pgtable.c

@@ -74,7 +74,7 @@ static struct page *maybe_pte_to_page(pte_t pte)
  * support falls into the same category.
  */
 
-static pte_t set_pte_filter(pte_t pte)
+static pte_t set_pte_filter_hash(pte_t pte)
 {
 	if (radix_enabled())
 		return pte;
@@ -93,14 +93,12 @@ static pte_t set_pte_filter(pte_t pte)
 	return pte;
 }
 
-static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
-				     int dirty)
-{
-	return pte;
-}
-
 #else /* CONFIG_PPC_BOOK3S */
 
+static pte_t set_pte_filter_hash(pte_t pte) { return pte; }
+
+#endif /* CONFIG_PPC_BOOK3S */
+
 /* Embedded type MMU with HW exec support. This is a bit more complicated
  * as we don't have two bits to spare for _PAGE_EXEC and _PAGE_HWEXEC so
  * instead we "filter out" the exec permission for non clean pages.
@@ -109,6 +107,9 @@ static pte_t set_pte_filter(pte_t pte)
 {
 	struct page *pg;
 
+	if (mmu_has_feature(MMU_FTR_HPTE_TABLE))
+		return set_pte_filter_hash(pte);
+
 	/* No exec permission in the first place, move on */
 	if (!pte_exec(pte) || !pte_looks_normal(pte))
 		return pte;
@@ -138,6 +139,9 @@ static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
 {
 	struct page *pg;
 
+	if (mmu_has_feature(MMU_FTR_HPTE_TABLE))
+		return pte;
+
 	/* So here, we only care about exec faults, as we use them
 	 * to recover lost _PAGE_EXEC and perform I$/D$ coherency
 	 * if necessary. Also if _PAGE_EXEC is already set, same deal,
@@ -172,8 +176,6 @@ static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
 	return pte_mkexec(pte);
 }
 
-#endif /* CONFIG_PPC_BOOK3S */
-
 /*
  * set_pte stores a linux PTE into the linux page table.
  */