[ARM] Improve non-executable support

Add support for detecting non-executable stack binaries, and adjust
permissions to prevent execution from data and stack areas.  Also,
ensure that READ_IMPLIES_EXEC is enabled for older CPUs where that
is true, and for any executable-stack binary.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/elf.h

@@ -18,9 +18,32 @@ typedef elf_greg_t elf_gregset_t[ELF_NGREG];
 typedef struct user_fp elf_fpregset_t;
 
 #define EM_ARM	40
-#define EF_ARM_APCS26 0x08
-#define EF_ARM_SOFT_FLOAT 0x200
-#define EF_ARM_EABI_MASK 0xFF000000
+
+#define EF_ARM_EABI_MASK	0xff000000
+#define EF_ARM_EABI_UNKNOWN	0x00000000
+#define EF_ARM_EABI_VER1	0x01000000
+#define EF_ARM_EABI_VER2	0x02000000
+#define EF_ARM_EABI_VER3	0x03000000
+#define EF_ARM_EABI_VER4	0x04000000
+#define EF_ARM_EABI_VER5	0x05000000
+
+#define EF_ARM_BE8		0x00800000	/* ABI 4,5 */
+#define EF_ARM_LE8		0x00400000	/* ABI 4,5 */
+#define EF_ARM_MAVERICK_FLOAT	0x00000800	/* ABI 0 */
+#define EF_ARM_VFP_FLOAT	0x00000400	/* ABI 0 */
+#define EF_ARM_SOFT_FLOAT	0x00000200	/* ABI 0 */
+#define EF_ARM_OLD_ABI		0x00000100	/* ABI 0 */
+#define EF_ARM_NEW_ABI		0x00000080	/* ABI 0 */
+#define EF_ARM_ALIGN8		0x00000040	/* ABI 0 */
+#define EF_ARM_PIC		0x00000020	/* ABI 0 */
+#define EF_ARM_MAPSYMSFIRST	0x00000010	/* ABI 2 */
+#define EF_ARM_APCS_FLOAT	0x00000010	/* ABI 0, floats in fp regs */
+#define EF_ARM_DYNSYMSUSESEGIDX	0x00000008	/* ABI 2 */
+#define EF_ARM_APCS_26		0x00000008	/* ABI 0 */
+#define EF_ARM_SYMSARESORTED	0x00000004	/* ABI 1,2 */
+#define EF_ARM_INTERWORK	0x00000004	/* ABI 0 */
+#define EF_ARM_HASENTRY		0x00000002	/* All */
+#define EF_ARM_RELEXEC		0x00000001	/* All */
 
 #define R_ARM_NONE	0
 #define R_ARM_PC24	1
@@ -57,23 +80,16 @@ typedef struct user_fp elf_fpregset_t;
 
 extern char elf_platform[];
 
-/*
- * This is used to ensure we don't load something for the wrong architecture.
- */
-#define elf_check_arch(x) ((x)->e_machine == EM_ARM && ELF_PROC_OK(x))
+struct elf32_hdr;
 
 /*
- * 32-bit code is always OK.  Some cpus can do 26-bit, some can't.
+ * This is used to ensure we don't load something for the wrong architecture.
  */
-#define ELF_PROC_OK(x)	(ELF_THUMB_OK(x) && ELF_26BIT_OK(x))
-
-#define ELF_THUMB_OK(x) \
-	((elf_hwcap & HWCAP_THUMB && ((x)->e_entry & 1) == 1) || \
-	 ((x)->e_entry & 3) == 0)
+extern int elf_check_arch(const struct elf32_hdr *);
+#define elf_check_arch elf_check_arch
 
-#define ELF_26BIT_OK(x) \
-	((elf_hwcap & HWCAP_26BIT && (x)->e_flags & EF_ARM_APCS26) || \
-	  ((x)->e_flags & EF_ARM_APCS26) == 0)
+extern int arm_elf_read_implies_exec(const struct elf32_hdr *, int);
+#define elf_read_implies_exec(ex,stk) arm_elf_read_implies_exec(&(ex), stk)
 
 #define USE_ELF_CORE_DUMP
 #define ELF_EXEC_PAGESIZE	4096
@@ -90,23 +106,7 @@ extern char elf_platform[];
    have no such handler.  */
 #define ELF_PLAT_INIT(_r, load_addr)	(_r)->ARM_r0 = 0
 
-/*
- * Since the FPA coprocessor uses CP1 and CP2, and iWMMXt uses CP0
- * and CP1, we only enable access to the iWMMXt coprocessor if the
- * binary is EABI or softfloat (and thus, guaranteed not to use
- * FPA instructions.)
- */
-#define SET_PERSONALITY(ex, ibcs2)					\
-	do {								\
-		if ((ex).e_flags & EF_ARM_APCS26) {			\
-			set_personality(PER_LINUX);			\
-		} else {						\
-			set_personality(PER_LINUX_32BIT);		\
-			if (elf_hwcap & HWCAP_IWMMXT && (ex).e_flags & (EF_ARM_EABI_MASK | EF_ARM_SOFT_FLOAT)) \
-				set_thread_flag(TIF_USING_IWMMXT);	\
-			else						\
-				clear_thread_flag(TIF_USING_IWMMXT);	\
-		}							\
-	} while (0)
+extern void elf_set_personality(const struct elf32_hdr *);
+#define SET_PERSONALITY(ex, ibcs2)	elf_set_personality(&(ex))
 
 #endif

arch/arm/include/asm/page.h

@@ -184,8 +184,9 @@ typedef struct page *pgtable_t;
 
 #endif /* !__ASSEMBLY__ */
 
-#define VM_DATA_DEFAULT_FLAGS	(VM_READ | VM_WRITE | VM_EXEC | \
-				 VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
+#define VM_DATA_DEFAULT_FLAGS \
+	(((current->personality & READ_IMPLIES_EXEC) ? VM_EXEC : 0) | \
+	 VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
 
 /*
  * With EABI on ARMv5 and above we must have 64-bit aligned slab pointers.

arch/arm/include/asm/pgtable.h

@@ -197,22 +197,29 @@ extern void __pgd_error(const char *file, int line, unsigned long val);
  * shared mapping bits.
  */
 #define _L_PTE_DEFAULT	L_PTE_PRESENT | L_PTE_YOUNG
-#define _L_PTE_READ	L_PTE_USER | L_PTE_EXEC
 
 extern pgprot_t		pgprot_user;
 extern pgprot_t		pgprot_kernel;
 
+#define _MOD_PROT(p, b)	__pgprot(pgprot_val(p) | (b))
+
 #define PAGE_NONE		pgprot_user
-#define PAGE_COPY	__pgprot(pgprot_val(pgprot_user) | _L_PTE_READ)
-#define PAGE_SHARED	__pgprot(pgprot_val(pgprot_user) | _L_PTE_READ | \
-				 L_PTE_WRITE)
-#define PAGE_READONLY	__pgprot(pgprot_val(pgprot_user) | _L_PTE_READ)
+#define PAGE_SHARED		_MOD_PROT(pgprot_user, L_PTE_USER | L_PTE_WRITE)
+#define PAGE_SHARED_EXEC	_MOD_PROT(pgprot_user, L_PTE_USER | L_PTE_WRITE | L_PTE_EXEC)
+#define PAGE_COPY		_MOD_PROT(pgprot_user, L_PTE_USER)
+#define PAGE_COPY_EXEC		_MOD_PROT(pgprot_user, L_PTE_USER | L_PTE_EXEC)
+#define PAGE_READONLY		_MOD_PROT(pgprot_user, L_PTE_USER)
+#define PAGE_READONLY_EXEC	_MOD_PROT(pgprot_user, L_PTE_USER | L_PTE_EXEC)
 #define PAGE_KERNEL		pgprot_kernel
+#define PAGE_KERNEL_EXEC	_MOD_PROT(pgprot_kernel, L_PTE_EXEC)
 
 #define __PAGE_NONE		__pgprot(_L_PTE_DEFAULT)
-#define __PAGE_COPY	__pgprot(_L_PTE_DEFAULT | _L_PTE_READ)
-#define __PAGE_SHARED	__pgprot(_L_PTE_DEFAULT | _L_PTE_READ | L_PTE_WRITE)
-#define __PAGE_READONLY	__pgprot(_L_PTE_DEFAULT | _L_PTE_READ)
+#define __PAGE_SHARED		__pgprot(_L_PTE_DEFAULT | L_PTE_USER | L_PTE_WRITE)
+#define __PAGE_SHARED_EXEC	__pgprot(_L_PTE_DEFAULT | L_PTE_USER | L_PTE_WRITE | L_PTE_EXEC)
+#define __PAGE_COPY		__pgprot(_L_PTE_DEFAULT | L_PTE_USER)
+#define __PAGE_COPY_EXEC	__pgprot(_L_PTE_DEFAULT | L_PTE_USER | L_PTE_EXEC)
+#define __PAGE_READONLY		__pgprot(_L_PTE_DEFAULT | L_PTE_USER)
+#define __PAGE_READONLY_EXEC	__pgprot(_L_PTE_DEFAULT | L_PTE_USER | L_PTE_EXEC)
 
 #endif /* __ASSEMBLY__ */
 
@@ -228,19 +235,19 @@ extern pgprot_t		pgprot_kernel;
 #define __P001  __PAGE_READONLY
 #define __P010  __PAGE_COPY
 #define __P011  __PAGE_COPY
-#define __P100  __PAGE_READONLY
-#define __P101  __PAGE_READONLY
-#define __P110  __PAGE_COPY
-#define __P111  __PAGE_COPY
+#define __P100  __PAGE_READONLY_EXEC
+#define __P101  __PAGE_READONLY_EXEC
+#define __P110  __PAGE_COPY_EXEC
+#define __P111  __PAGE_COPY_EXEC
 
 #define __S000  __PAGE_NONE
 #define __S001  __PAGE_READONLY
 #define __S010  __PAGE_SHARED
 #define __S011  __PAGE_SHARED
-#define __S100  __PAGE_READONLY
-#define __S101  __PAGE_READONLY
-#define __S110  __PAGE_SHARED
-#define __S111  __PAGE_SHARED
+#define __S100  __PAGE_READONLY_EXEC
+#define __S101  __PAGE_READONLY_EXEC
+#define __S110  __PAGE_SHARED_EXEC
+#define __S111  __PAGE_SHARED_EXEC
 
 #ifndef __ASSEMBLY__
 /*

arch/arm/kernel/Makefile

@@ -10,7 +10,7 @@ endif
 
 # Object file lists.
 
-obj-y		:= compat.o entry-armv.o entry-common.o irq.o \
+obj-y		:= compat.o elf.o entry-armv.o entry-common.o irq.o \
 		   process.o ptrace.o setup.o signal.o \
 		   sys_arm.o stacktrace.o time.o traps.o
 

arch/arm/kernel/elf.c

+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/personality.h>
+#include <linux/binfmts.h>
+#include <linux/elf.h>
+
+int elf_check_arch(const struct elf32_hdr *x)
+{
+	unsigned int eflags;
+
+	/* Make sure it's an ARM executable */
+	if (x->e_machine != EM_ARM)
+		return 0;
+
+	/* Make sure the entry address is reasonable */
+	if (x->e_entry & 1) {
+		if (!(elf_hwcap & HWCAP_THUMB))
+			return 0;
+	} else if (x->e_entry & 3)
+		return 0;
+
+	eflags = x->e_flags;
+	if ((eflags & EF_ARM_EABI_MASK) == EF_ARM_EABI_UNKNOWN) {
+		/* APCS26 is only allowed if the CPU supports it */
+		if ((eflags & EF_ARM_APCS_26) && !(elf_hwcap & HWCAP_26BIT))
+			return 0;
+
+		/* VFP requires the supporting code */
+		if ((eflags & EF_ARM_VFP_FLOAT) && !(elf_hwcap & HWCAP_VFP))
+			return 0;
+	}
+	return 1;
+}
+EXPORT_SYMBOL(elf_check_arch);
+
+void elf_set_personality(const struct elf32_hdr *x)
+{
+	unsigned int eflags = x->e_flags;
+	unsigned int personality = PER_LINUX_32BIT;
+
+	/*
+	 * APCS-26 is only valid for OABI executables
+	 */
+	if ((eflags & EF_ARM_EABI_MASK) == EF_ARM_EABI_UNKNOWN) {
+		if (eflags & EF_ARM_APCS_26)
+			personality = PER_LINUX;
+	}
+
+	set_personality(personality);
+
+	/*
+	 * Since the FPA coprocessor uses CP1 and CP2, and iWMMXt uses CP0
+	 * and CP1, we only enable access to the iWMMXt coprocessor if the
+	 * binary is EABI or softfloat (and thus, guaranteed not to use
+	 * FPA instructions.)
+	 */
+	if (elf_hwcap & HWCAP_IWMMXT &&
+	    eflags & (EF_ARM_EABI_MASK | EF_ARM_SOFT_FLOAT)) {
+		set_thread_flag(TIF_USING_IWMMXT);
+	} else {
+		clear_thread_flag(TIF_USING_IWMMXT);
+	}
+}
+EXPORT_SYMBOL(elf_set_personality);
+
+/*
+ * Set READ_IMPLIES_EXEC if:
+ *  - the binary requires an executable stack
+ *  - we're running on a CPU which doesn't support NX.
+ */
+int arm_elf_read_implies_exec(const struct elf32_hdr *x, int executable_stack)
+{
+	if (executable_stack != EXSTACK_ENABLE_X)
+		return 1;
+	if (cpu_architecture() <= CPU_ARCH_ARMv6)
+		return 1;
+	return 0;
+}
+EXPORT_SYMBOL(arm_elf_read_implies_exec);

arch/arm/kernel/module.c

@@ -47,7 +47,7 @@ void *module_alloc(unsigned long size)
 	if (!area)
 		return NULL;
 
-	return __vmalloc_area(area, GFP_KERNEL, PAGE_KERNEL);
+	return __vmalloc_area(area, GFP_KERNEL, PAGE_KERNEL_EXEC);
 }
 #else /* CONFIG_MMU */
 void *module_alloc(unsigned long size)