[S390] noexec protection

This provides a noexec protection on s390 hardware. Our hardware does
not have any bits left in the pte for a hw noexec bit, so this is a
different approach using shadow page tables and a special addressing
mode that allows separate address spaces for code and data.

As a special feature of our "secondary-space" addressing mode, separate
page tables can be specified for the translation of data addresses
(storage operands) and instruction addresses. The shadow page table is
used for the instruction addresses and the standard page table for the
data addresses.
The shadow page table is linked to the standard page table by a pointer
in page->lru.next of the struct page corresponding to the page that
contains the standard page table (since page->private is not really
private with the pte_lock and the page table pages are not in the LRU
list).
Depending on the software bits of a pte, it is either inserted into
both page tables or just into the standard (data) page table. Pages of
a vma that does not have the VM_EXEC bit set get mapped only in the
data address space. Any try to execute code on such a page will cause a
page translation exception. The standard reaction to this is a SIGSEGV
with two exceptions: the two system call opcodes 0x0a77 (sys_sigreturn)
and 0x0aad (sys_rt_sigreturn) are allowed. They are stored by the
kernel to the signal stack frame. Unfortunately, the signal return
mechanism cannot be modified to use an SA_RESTORER because the
exception unwinding code depends on the system call opcode stored
behind the signal stack frame.

This feature requires that user space is executed in secondary-space
mode and the kernel in home-space mode, which means that the addressing
modes need to be switched and that the noexec protection only works
for user space.
After switching the addressing modes, we cannot use the mvcp/mvcs
instructions anymore to copy between kernel and user space. A new
mvcos instruction has been added to the z9 EC/BC hardware which allows
to copy between arbitrary address spaces, but on older hardware the
page tables need to be walked manually.

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

16 files changed, 606 insertions, 61 deletions

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 1227236..5c7e981 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -134,6 +134,31 @@ config AUDIT_ARCH
 	bool
 	default y
 
+config S390_SWITCH_AMODE
+	bool "Switch kernel/user addressing modes"
+	help
+	  This option allows to switch the addressing modes of kernel and user
+	  space. The kernel parameter switch_amode=on will enable this feature,
+	  default is disabled. Enabling this (via kernel parameter) on machines
+	  earlier than IBM System z9-109 EC/BC will reduce system performance.
+
+	  Note that this option will also be selected by selecting the execute
+	  protection option below. Enabling the execute protection via the
+	  noexec kernel parameter will also switch the addressing modes,
+	  independent of the switch_amode kernel parameter.
+
+
+config S390_EXEC_PROTECT
+	bool "Data execute protection"
+	select S390_SWITCH_AMODE
+	help
+	  This option allows to enable a buffer overflow protection for user
+	  space programs and it also selects the addressing mode option above.
+	  The kernel parameter noexec=on will enable this feature and also
+	  switch the addressing modes, default is disabled. Enabling this (via
+	  kernel parameter) on machines earlier than IBM System z9-109 EC/BC
+	  will reduce system performance.
+
 comment "Code generation options"
 
 choice
diff --git a/arch/s390/defconfig b/arch/s390/defconfig
index 46bb385..12eb97f 100644
--- a/arch/s390/defconfig
+++ b/arch/s390/defconfig
@@ -108,6 +108,8 @@ CONFIG_DEFAULT_MIGRATION_COST=1000000
 CONFIG_COMPAT=y
 CONFIG_SYSVIPC_COMPAT=y
 CONFIG_AUDIT_ARCH=y
+CONFIG_S390_SWITCH_AMODE=y
+CONFIG_S390_EXEC_PROTECT=y
 
 #
 # Code generation options
diff --git a/arch/s390/kernel/compat_linux.c b/arch/s390/kernel/compat_linux.c
index cf84d69..666bb6d 100644
--- a/arch/s390/kernel/compat_linux.c
+++ b/arch/s390/kernel/compat_linux.c
@@ -69,6 +69,12 @@
 
 #include "compat_linux.h"
 
+long psw_user32_bits	= (PSW_BASE32_BITS | PSW_MASK_DAT | PSW_ASC_HOME |
+			   PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK |
+			   PSW_MASK_PSTATE | PSW_DEFAULT_KEY);
+long psw32_user_bits	= (PSW32_BASE_BITS | PSW32_MASK_DAT | PSW32_ASC_HOME |
+			   PSW32_MASK_IO | PSW32_MASK_EXT | PSW32_MASK_MCHECK |
+			   PSW32_MASK_PSTATE);
  
 /* For this source file, we want overflow handling. */
 
diff --git a/arch/s390/kernel/compat_linux.h b/arch/s390/kernel/compat_linux.h
index 1a18e29..e89f8c0 100644
--- a/arch/s390/kernel/compat_linux.h
+++ b/arch/s390/kernel/compat_linux.h
@@ -115,37 +115,6 @@ typedef struct
         __u32	addr;
 } _psw_t32 __attribute__ ((aligned(8)));
 
-#define PSW32_MASK_PER		0x40000000UL
-#define PSW32_MASK_DAT		0x04000000UL
-#define PSW32_MASK_IO		0x02000000UL
-#define PSW32_MASK_EXT		0x01000000UL
-#define PSW32_MASK_KEY		0x00F00000UL
-#define PSW32_MASK_MCHECK	0x00040000UL
-#define PSW32_MASK_WAIT		0x00020000UL
-#define PSW32_MASK_PSTATE	0x00010000UL
-#define PSW32_MASK_ASC		0x0000C000UL
-#define PSW32_MASK_CC		0x00003000UL
-#define PSW32_MASK_PM		0x00000f00UL
-
-#define PSW32_ADDR_AMODE31	0x80000000UL
-#define PSW32_ADDR_INSN		0x7FFFFFFFUL
-
-#define PSW32_BASE_BITS		0x00080000UL
-
-#define PSW32_ASC_PRIMARY	0x00000000UL
-#define PSW32_ASC_ACCREG	0x00004000UL
-#define PSW32_ASC_SECONDARY	0x00008000UL
-#define PSW32_ASC_HOME		0x0000C000UL
-
-#define PSW32_USER_BITS	(PSW32_BASE_BITS | PSW32_MASK_DAT | PSW32_ASC_HOME | \
-			 PSW32_MASK_IO | PSW32_MASK_EXT | PSW32_MASK_MCHECK | \
-			 PSW32_MASK_PSTATE)
-
-#define PSW32_MASK_MERGE(CURRENT,NEW) \
-        (((CURRENT) & ~(PSW32_MASK_CC|PSW32_MASK_PM)) | \
-         ((NEW) & (PSW32_MASK_CC|PSW32_MASK_PM)))
-
-
 typedef struct
 {
 	_psw_t32	psw;
diff --git a/arch/s390/kernel/compat_signal.c b/arch/s390/kernel/compat_signal.c
index 8d17b2a..887a988 100644
--- a/arch/s390/kernel/compat_signal.c
+++ b/arch/s390/kernel/compat_signal.c
@@ -298,7 +298,7 @@ static int save_sigregs32(struct pt_regs *regs, _sigregs32 __user *sregs)
 	_s390_regs_common32 regs32;
 	int err, i;
 
-	regs32.psw.mask = PSW32_MASK_MERGE(PSW32_USER_BITS,
+	regs32.psw.mask = PSW32_MASK_MERGE(psw32_user_bits,
 					   (__u32)(regs->psw.mask >> 32));
 	regs32.psw.addr = PSW32_ADDR_AMODE31 | (__u32) regs->psw.addr;
 	for (i = 0; i < NUM_GPRS; i++)
diff --git a/arch/s390/kernel/ipl.c b/arch/s390/kernel/ipl.c
index 9e9972e..2c91226 100644
--- a/arch/s390/kernel/ipl.c
+++ b/arch/s390/kernel/ipl.c
@@ -1016,12 +1016,12 @@ void s390_reset_system(void)
 	__ctl_clear_bit(0,28);
 
 	/* Set new machine check handler */
-	S390_lowcore.mcck_new_psw.mask = PSW_KERNEL_BITS & ~PSW_MASK_MCHECK;
+	S390_lowcore.mcck_new_psw.mask = psw_kernel_bits & ~PSW_MASK_MCHECK;
 	S390_lowcore.mcck_new_psw.addr =
 		PSW_ADDR_AMODE | (unsigned long) &reset_mcck_handler;
 
 	/* Set new program check handler */
-	S390_lowcore.program_new_psw.mask = PSW_KERNEL_BITS & ~PSW_MASK_MCHECK;
+	S390_lowcore.program_new_psw.mask = psw_kernel_bits & ~PSW_MASK_MCHECK;
 	S390_lowcore.program_new_psw.addr =
 		PSW_ADDR_AMODE | (unsigned long) &reset_pgm_handler;
 
diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index 6603fbb..5acfac6 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -144,7 +144,7 @@ static void default_idle(void)
 
 	trace_hardirqs_on();
 	/* Wait for external, I/O or machine check interrupt. */
-	__load_psw_mask(PSW_KERNEL_BITS | PSW_MASK_WAIT |
+	__load_psw_mask(psw_kernel_bits | PSW_MASK_WAIT |
 			PSW_MASK_IO | PSW_MASK_EXT);
 }
 
@@ -190,7 +190,7 @@ int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
 	struct pt_regs regs;
 
 	memset(&regs, 0, sizeof(regs));
-	regs.psw.mask = PSW_KERNEL_BITS | PSW_MASK_IO | PSW_MASK_EXT;
+	regs.psw.mask = psw_kernel_bits | PSW_MASK_IO | PSW_MASK_EXT;
 	regs.psw.addr = (unsigned long) kernel_thread_starter | PSW_ADDR_AMODE;
 	regs.gprs[9] = (unsigned long) fn;
 	regs.gprs[10] = (unsigned long) arg;
diff --git a/arch/s390/kernel/ptrace.c b/arch/s390/kernel/ptrace.c
index 29fde70..2a8f087 100644
--- a/arch/s390/kernel/ptrace.c
+++ b/arch/s390/kernel/ptrace.c
@@ -230,9 +230,9 @@ poke_user(struct task_struct *child, addr_t addr, addr_t data)
 		 */
 		if (addr == (addr_t) &dummy->regs.psw.mask &&
 #ifdef CONFIG_COMPAT
-		    data != PSW_MASK_MERGE(PSW_USER32_BITS, data) &&
+		    data != PSW_MASK_MERGE(psw_user32_bits, data) &&
 #endif
-		    data != PSW_MASK_MERGE(PSW_USER_BITS, data))
+		    data != PSW_MASK_MERGE(psw_user_bits, data))
 			/* Invalid psw mask. */
 			return -EINVAL;
 #ifndef CONFIG_64BIT
@@ -393,7 +393,7 @@ peek_user_emu31(struct task_struct *child, addr_t addr, addr_t data)
 		if (addr == (addr_t) &dummy32->regs.psw.mask) {
 			/* Fake a 31 bit psw mask. */
 			tmp = (__u32)(task_pt_regs(child)->psw.mask >> 32);
-			tmp = PSW32_MASK_MERGE(PSW32_USER_BITS, tmp);
+			tmp = PSW32_MASK_MERGE(psw32_user_bits, tmp);
 		} else if (addr == (addr_t) &dummy32->regs.psw.addr) {
 			/* Fake a 31 bit psw address. */
 			tmp = (__u32) task_pt_regs(child)->psw.addr |
@@ -468,11 +468,11 @@ poke_user_emu31(struct task_struct *child, addr_t addr, addr_t data)
 		 */
 		if (addr == (addr_t) &dummy32->regs.psw.mask) {
 			/* Build a 64 bit psw mask from 31 bit mask. */
-			if (tmp != PSW32_MASK_MERGE(PSW32_USER_BITS, tmp))
+			if (tmp != PSW32_MASK_MERGE(psw32_user_bits, tmp))
 				/* Invalid psw mask. */
 				return -EINVAL;
 			task_pt_regs(child)->psw.mask =
-				PSW_MASK_MERGE(PSW_USER32_BITS, (__u64) tmp << 32);
+				PSW_MASK_MERGE(psw_user32_bits, (__u64) tmp << 32);
 		} else if (addr == (addr_t) &dummy32->regs.psw.addr) {
 			/* Build a 64 bit psw address from 31 bit address. */
 			task_pt_regs(child)->psw.addr =
diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
index 25bf727..b1b9a93 100644
--- a/arch/s390/kernel/setup.c
+++ b/arch/s390/kernel/setup.c
@@ -50,6 +50,13 @@
 #include <asm/page.h>
 #include <asm/ptrace.h>
 #include <asm/sections.h>
+#include <asm/compat.h>
+
+long psw_kernel_bits	= (PSW_BASE_BITS | PSW_MASK_DAT | PSW_ASC_PRIMARY |
+			   PSW_MASK_MCHECK | PSW_DEFAULT_KEY);
+long psw_user_bits	= (PSW_BASE_BITS | PSW_MASK_DAT | PSW_ASC_HOME |
+			   PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK |
+			   PSW_MASK_PSTATE | PSW_DEFAULT_KEY);
 
 /*
  * User copy operations.
@@ -383,6 +390,84 @@ static int __init early_parse_ipldelay(char *p)
 }
 early_param("ipldelay", early_parse_ipldelay);
 
+#ifdef CONFIG_S390_SWITCH_AMODE
+unsigned int switch_amode = 0;
+EXPORT_SYMBOL_GPL(switch_amode);
+
+static inline void set_amode_and_uaccess(unsigned long user_amode,
+					 unsigned long user32_amode)
+{
+	psw_user_bits = PSW_BASE_BITS | PSW_MASK_DAT | user_amode |
+			PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK |
+			PSW_MASK_PSTATE | PSW_DEFAULT_KEY;
+#ifdef CONFIG_COMPAT
+	psw_user32_bits = PSW_BASE32_BITS | PSW_MASK_DAT | user_amode |
+			  PSW_MASK_IO | PSW_MASK_EXT | PSW_MASK_MCHECK |
+			  PSW_MASK_PSTATE | PSW_DEFAULT_KEY;
+	psw32_user_bits = PSW32_BASE_BITS | PSW32_MASK_DAT | user32_amode |
+			  PSW32_MASK_IO | PSW32_MASK_EXT | PSW32_MASK_MCHECK |
+			  PSW32_MASK_PSTATE;
+#endif
+	psw_kernel_bits = PSW_BASE_BITS | PSW_MASK_DAT | PSW_ASC_HOME |
+			  PSW_MASK_MCHECK | PSW_DEFAULT_KEY;
+
+	if (MACHINE_HAS_MVCOS) {
+		printk("mvcos available.\n");
+		memcpy(&uaccess, &uaccess_mvcos_switch, sizeof(uaccess));
+	} else {
+		printk("mvcos not available.\n");
+		memcpy(&uaccess, &uaccess_pt, sizeof(uaccess));
+	}
+}
+
+/*
+ * Switch kernel/user addressing modes?
+ */
+static int __init early_parse_switch_amode(char *p)
+{
+	switch_amode = 1;
+	return 0;
+}
+early_param("switch_amode", early_parse_switch_amode);
+
+#else /* CONFIG_S390_SWITCH_AMODE */
+static inline void set_amode_and_uaccess(unsigned long user_amode,
+					 unsigned long user32_amode)
+{
+}
+#endif /* CONFIG_S390_SWITCH_AMODE */
+
+#ifdef CONFIG_S390_EXEC_PROTECT
+unsigned int s390_noexec = 0;
+EXPORT_SYMBOL_GPL(s390_noexec);
+
+/*
+ * Enable execute protection?
+ */
+static int __init early_parse_noexec(char *p)
+{
+	if (!strncmp(p, "off", 3))
+		return 0;
+	switch_amode = 1;
+	s390_noexec = 1;
+	return 0;
+}
+early_param("noexec", early_parse_noexec);
+#endif /* CONFIG_S390_EXEC_PROTECT */
+
+static void setup_addressing_mode(void)
+{
+	if (s390_noexec) {
+		printk("S390 execute protection active, ");
+		set_amode_and_uaccess(PSW_ASC_SECONDARY, PSW32_ASC_SECONDARY);
+		return;
+	}
+	if (switch_amode) {
+		printk("S390 address spaces switched, ");
+		set_amode_and_uaccess(PSW_ASC_PRIMARY, PSW32_ASC_PRIMARY);
+	}
+}
+
 static void __init
 setup_lowcore(void)
 {
@@ -399,19 +484,21 @@ setup_lowcore(void)
 	lc->restart_psw.mask = PSW_BASE_BITS | PSW_DEFAULT_KEY;
 	lc->restart_psw.addr =
 		PSW_ADDR_AMODE | (unsigned long) restart_int_handler;
-	lc->external_new_psw.mask = PSW_KERNEL_BITS;
+	if (switch_amode)
+		lc->restart_psw.mask |= PSW_ASC_HOME;
+	lc->external_new_psw.mask = psw_kernel_bits;
 	lc->external_new_psw.addr =
 		PSW_ADDR_AMODE | (unsigned long) ext_int_handler;
-	lc->svc_new_psw.mask = PSW_KERNEL_BITS | PSW_MASK_IO | PSW_MASK_EXT;
+	lc->svc_new_psw.mask = psw_kernel_bits | PSW_MASK_IO | PSW_MASK_EXT;
 	lc->svc_new_psw.addr = PSW_ADDR_AMODE | (unsigned long) system_call;
-	lc->program_new_psw.mask = PSW_KERNEL_BITS;
+	lc->program_new_psw.mask = psw_kernel_bits;
 	lc->program_new_psw.addr =
 		PSW_ADDR_AMODE | (unsigned long)pgm_check_handler;
 	lc->mcck_new_psw.mask =
-		PSW_KERNEL_BITS & ~PSW_MASK_MCHECK & ~PSW_MASK_DAT;
+		psw_kernel_bits & ~PSW_MASK_MCHECK & ~PSW_MASK_DAT;
 	lc->mcck_new_psw.addr =
 		PSW_ADDR_AMODE | (unsigned long) mcck_int_handler;
-	lc->io_new_psw.mask = PSW_KERNEL_BITS;
+	lc->io_new_psw.mask = psw_kernel_bits;
 	lc->io_new_psw.addr = PSW_ADDR_AMODE | (unsigned long) io_int_handler;
 	lc->ipl_device = S390_lowcore.ipl_device;
 	lc->jiffy_timer = -1LL;
@@ -645,6 +732,7 @@ setup_arch(char **cmdline_p)
 	parse_early_param();
 
 	setup_memory_end();
+	setup_addressing_mode();
 	setup_memory();
 	setup_resources();
 	setup_lowcore();
diff --git a/arch/s390/kernel/signal.c b/arch/s390/kernel/signal.c
index 4c8a795..554f9cf 100644
--- a/arch/s390/kernel/signal.c
+++ b/arch/s390/kernel/signal.c
@@ -119,7 +119,7 @@ static int save_sigregs(struct pt_regs *regs, _sigregs __user *sregs)
 
 	/* Copy a 'clean' PSW mask to the user to avoid leaking
 	   information about whether PER is currently on.  */
-	user_sregs.regs.psw.mask = PSW_MASK_MERGE(PSW_USER_BITS, regs->psw.mask);
+	user_sregs.regs.psw.mask = PSW_MASK_MERGE(psw_user_bits, regs->psw.mask);
 	user_sregs.regs.psw.addr = regs->psw.addr;
 	memcpy(&user_sregs.regs.gprs, &regs->gprs, sizeof(sregs->regs.gprs));
 	memcpy(&user_sregs.regs.acrs, current->thread.acrs,
diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 3cb7e10..cb155d9 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -244,7 +244,7 @@ static inline void do_wait_for_stop(void)
 void smp_send_stop(void)
 {
 	/* Disable all interrupts/machine checks */
-	__load_psw_mask(PSW_KERNEL_BITS & ~PSW_MASK_MCHECK);
+	__load_psw_mask(psw_kernel_bits & ~PSW_MASK_MCHECK);
 
         /* write magic number to zero page (absolute 0) */
 	lowcore_ptr[smp_processor_id()]->panic_magic = __PANIC_MAGIC;
diff --git a/arch/s390/lib/uaccess_mvcos.c b/arch/s390/lib/uaccess_mvcos.c
index 78c48f8..6d87723 100644
--- a/arch/s390/lib/uaccess_mvcos.c
+++ b/arch/s390/lib/uaccess_mvcos.c
@@ -162,6 +162,44 @@ static size_t clear_user_mvcos(size_t size, void __user *to)
 	return size;
 }
 
+static size_t strnlen_user_mvcos(size_t count, const char __user *src)
+{
+	char buf[256];
+	int rc;
+	size_t done, len, len_str;
+
+	done = 0;
+	do {
+		len = min(count - done, (size_t) 256);
+		rc = uaccess.copy_from_user(len, src + done, buf);
+		if (unlikely(rc == len))
+			return 0;
+		len -= rc;
+		len_str = strnlen(buf, len);
+		done += len_str;
+	} while ((len_str == len) && (done < count));
+	return done + 1;
+}
+
+static size_t strncpy_from_user_mvcos(size_t count, const char __user *src,
+				      char *dst)
+{
+	int rc;
+	size_t done, len, len_str;
+
+	done = 0;
+	do {
+		len = min(count - done, (size_t) 4096);
+		rc = uaccess.copy_from_user(len, src + done, dst);
+		if (unlikely(rc == len))
+			return -EFAULT;
+		len -= rc;
+		len_str = strnlen(dst, len);
+		done += len_str;
+	} while ((len_str == len) && (done < count));
+	return done;
+}
+
 struct uaccess_ops uaccess_mvcos = {
 	.copy_from_user = copy_from_user_mvcos_check,
 	.copy_from_user_small = copy_from_user_std,
@@ -174,3 +212,18 @@ struct uaccess_ops uaccess_mvcos = {
 	.futex_atomic_op = futex_atomic_op_std,
 	.futex_atomic_cmpxchg = futex_atomic_cmpxchg_std,
 };
+
+#ifdef CONFIG_S390_SWITCH_AMODE
+struct uaccess_ops uaccess_mvcos_switch = {
+	.copy_from_user = copy_from_user_mvcos,
+	.copy_from_user_small = copy_from_user_mvcos,
+	.copy_to_user = copy_to_user_mvcos,
+	.copy_to_user_small = copy_to_user_mvcos,
+	.copy_in_user = copy_in_user_mvcos,
+	.clear_user = clear_user_mvcos,
+	.strnlen_user = strnlen_user_mvcos,
+	.strncpy_from_user = strncpy_from_user_mvcos,
+	.futex_atomic_op = futex_atomic_op_pt,
+	.futex_atomic_cmpxchg = futex_atomic_cmpxchg_pt,
+};
+#endif
diff --git a/arch/s390/lib/uaccess_pt.c b/arch/s390/lib/uaccess_pt.c
index 24ead55..637192f 100644
--- a/arch/s390/lib/uaccess_pt.c
+++ b/arch/s390/lib/uaccess_pt.c
@@ -1,7 +1,8 @@
 /*
  *  arch/s390/lib/uaccess_pt.c
  *
- *  User access functions based on page table walks.
+ *  User access functions based on page table walks for enhanced
+ *  system layout without hardware support.
  *
  *    Copyright IBM Corp. 2006
  *    Author(s): Gerald Schaefer (gerald.schaefer@de.ibm.com)
@@ -134,6 +135,49 @@ fault:
 	goto retry;
 }
 
+/*
+ * Do DAT for user address by page table walk, return kernel address.
+ * This function needs to be called with current->mm->page_table_lock held.
+ */
+static inline unsigned long __dat_user_addr(unsigned long uaddr)
+{
+	struct mm_struct *mm = current->mm;
+	unsigned long pfn, ret;
+	pgd_t *pgd;
+	pmd_t *pmd;
+	pte_t *pte;
+	int rc;
+
+	ret = 0;
+retry:
+	pgd = pgd_offset(mm, uaddr);
+	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+		goto fault;
+
+	pmd = pmd_offset(pgd, uaddr);
+	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+		goto fault;
+
+	pte = pte_offset_map(pmd, uaddr);
+	if (!pte || !pte_present(*pte))
+		goto fault;
+
+	pfn = pte_pfn(*pte);
+	if (!pfn_valid(pfn))
+		goto out;
+
+	ret = (pfn << PAGE_SHIFT) + (uaddr & (PAGE_SIZE - 1));
+out:
+	return ret;
+fault:
+	spin_unlock(&mm->page_table_lock);
+	rc = __handle_fault(mm, uaddr, 0);
+	spin_lock(&mm->page_table_lock);
+	if (rc)
+		goto out;
+	goto retry;
+}
+
 size_t copy_from_user_pt(size_t n, const void __user *from, void *to)
 {
 	size_t rc;
@@ -156,3 +200,277 @@ size_t copy_to_user_pt(size_t n, void __user *to, const void *from)
 	}
 	return __user_copy_pt((unsigned long) to, (void *) from, n, 1);
 }
+
+static size_t clear_user_pt(size_t n, void __user *to)
+{
+	long done, size, ret;
+
+	if (segment_eq(get_fs(), KERNEL_DS)) {
+		memset((void __kernel __force *) to, 0, n);
+		return 0;
+	}
+	done = 0;
+	do {
+		if (n - done > PAGE_SIZE)
+			size = PAGE_SIZE;
+		else
+			size = n - done;
+		ret = __user_copy_pt((unsigned long) to + done,
+				      &empty_zero_page, size, 1);
+		done += size;
+		if (ret)
+			return ret + n - done;
+	} while (done < n);
+	return 0;
+}
+
+static size_t strnlen_user_pt(size_t count, const char __user *src)
+{
+	char *addr;
+	unsigned long uaddr = (unsigned long) src;
+	struct mm_struct *mm = current->mm;
+	unsigned long offset, pfn, done, len;
+	pgd_t *pgd;
+	pmd_t *pmd;
+	pte_t *pte;
+	size_t len_str;
+
+	if (segment_eq(get_fs(), KERNEL_DS))
+		return strnlen((const char __kernel __force *) src, count) + 1;
+	done = 0;
+retry:
+	spin_lock(&mm->page_table_lock);
+	do {
+		pgd = pgd_offset(mm, uaddr);
+		if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+			goto fault;
+
+		pmd = pmd_offset(pgd, uaddr);
+		if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+			goto fault;
+
+		pte = pte_offset_map(pmd, uaddr);
+		if (!pte || !pte_present(*pte))
+			goto fault;
+
+		pfn = pte_pfn(*pte);
+		if (!pfn_valid(pfn)) {
+			done = -1;
+			goto out;
+		}
+
+		offset = uaddr & (PAGE_SIZE-1);
+		addr = (char *)(pfn << PAGE_SHIFT) + offset;
+		len = min(count - done, PAGE_SIZE - offset);
+		len_str = strnlen(addr, len);
+		done += len_str;
+		uaddr += len_str;
+	} while ((len_str == len) && (done < count));
+out:
+	spin_unlock(&mm->page_table_lock);
+	return done + 1;
+fault:
+	spin_unlock(&mm->page_table_lock);
+	if (__handle_fault(mm, uaddr, 0)) {
+		return 0;
+	}
+	goto retry;
+}
+
+static size_t strncpy_from_user_pt(size_t count, const char __user *src,
+				   char *dst)
+{
+	size_t n = strnlen_user_pt(count, src);
+
+	if (!n)
+		return -EFAULT;
+	if (n > count)
+		n = count;
+	if (segment_eq(get_fs(), KERNEL_DS)) {
+		memcpy(dst, (const char __kernel __force *) src, n);
+		if (dst[n-1] == '\0')
+			return n-1;
+		else
+			return n;
+	}
+	if (__user_copy_pt((unsigned long) src, dst, n, 0))
+		return -EFAULT;
+	if (dst[n-1] == '\0')
+		return n-1;
+	else
+		return n;
+}
+
+static size_t copy_in_user_pt(size_t n, void __user *to,
+			      const void __user *from)
+{
+	struct mm_struct *mm = current->mm;
+	unsigned long offset_from, offset_to, offset_max, pfn_from, pfn_to,
+		      uaddr, done, size;
+	unsigned long uaddr_from = (unsigned long) from;
+	unsigned long uaddr_to = (unsigned long) to;
+	pgd_t *pgd_from, *pgd_to;
+	pmd_t *pmd_from, *pmd_to;
+	pte_t *pte_from, *pte_to;
+	int write_user;
+
+	done = 0;
+retry:
+	spin_lock(&mm->page_table_lock);
+	do {
+		pgd_from = pgd_offset(mm, uaddr_from);
+		if (pgd_none(*pgd_from) || unlikely(pgd_bad(*pgd_from))) {
+			uaddr = uaddr_from;
+			write_user = 0;
+			goto fault;
+		}
+		pgd_to = pgd_offset(mm, uaddr_to);
+		if (pgd_none(*pgd_to) || unlikely(pgd_bad(*pgd_to))) {
+			uaddr = uaddr_to;
+			write_user = 1;
+			goto fault;
+		}
+
+		pmd_from = pmd_offset(pgd_from, uaddr_from);
+		if (pmd_none(*pmd_from) || unlikely(pmd_bad(*pmd_from))) {
+			uaddr = uaddr_from;
+			write_user = 0;
+			goto fault;
+		}
+		pmd_to = pmd_offset(pgd_to, uaddr_to);
+		if (pmd_none(*pmd_to) || unlikely(pmd_bad(*pmd_to))) {
+			uaddr = uaddr_to;
+			write_user = 1;
+			goto fault;
+		}
+
+		pte_from = pte_offset_map(pmd_from, uaddr_from);
+		if (!pte_from || !pte_present(*pte_from)) {
+			uaddr = uaddr_from;
+			write_user = 0;
+			goto fault;
+		}
+		pte_to = pte_offset_map(pmd_to, uaddr_to);
+		if (!pte_to || !pte_present(*pte_to) || !pte_write(*pte_to)) {
+			uaddr = uaddr_to;
+			write_user = 1;
+			goto fault;
+		}
+
+		pfn_from = pte_pfn(*pte_from);
+		if (!pfn_valid(pfn_from))
+			goto out;
+		pfn_to = pte_pfn(*pte_to);
+		if (!pfn_valid(pfn_to))
+			goto out;
+
+		offset_from = uaddr_from & (PAGE_SIZE-1);
+		offset_to = uaddr_from & (PAGE_SIZE-1);
+		offset_max = max(offset_from, offset_to);
+		size = min(n - done, PAGE_SIZE - offset_max);
+
+		memcpy((void *)(pfn_to << PAGE_SHIFT) + offset_to,
+		       (void *)(pfn_from << PAGE_SHIFT) + offset_from, size);
+		done += size;
+		uaddr_from += size;
+		uaddr_to += size;
+	} while (done < n);
+out:
+	spin_unlock(&mm->page_table_lock);
+	return n - done;
+fault:
+	spin_unlock(&mm->page_table_lock);
+	if (__handle_fault(mm, uaddr, write_user))
+		return n - done;
+	goto retry;
+}
+
+#define __futex_atomic_op(insn, ret, oldval, newval, uaddr, oparg)	\
+	asm volatile("0: l   %1,0(%6)\n"				\
+		     "1: " insn						\
+		     "2: cs  %1,%2,0(%6)\n"				\
+		     "3: jl  1b\n"					\
+		     "   lhi %0,0\n"					\
+		     "4:\n"						\
+		     EX_TABLE(0b,4b) EX_TABLE(2b,4b) EX_TABLE(3b,4b)	\
+		     : "=d" (ret), "=&d" (oldval), "=&d" (newval),	\
+		       "=m" (*uaddr)					\
+		     : "0" (-EFAULT), "d" (oparg), "a" (uaddr),		\
+		       "m" (*uaddr) : "cc" );
+
+int futex_atomic_op_pt(int op, int __user *uaddr, int oparg, int *old)
+{
+	int oldval = 0, newval, ret;
+
+	spin_lock(&current->mm->page_table_lock);
+	uaddr = (int __user *) __dat_user_addr((unsigned long) uaddr);
+	if (!uaddr) {
+		spin_unlock(&current->mm->page_table_lock);
+		return -EFAULT;
+	}
+	get_page(virt_to_page(uaddr));
+	spin_unlock(&current->mm->page_table_lock);
+	switch (op) {
+	case FUTEX_OP_SET:
+		__futex_atomic_op("lr %2,%5\n",
+				  ret, oldval, newval, uaddr, oparg);
+		break;
+	case FUTEX_OP_ADD:
+		__futex_atomic_op("lr %2,%1\nar %2,%5\n",
+				  ret, oldval, newval, uaddr, oparg);
+		break;
+	case FUTEX_OP_OR:
+		__futex_atomic_op("lr %2,%1\nor %2,%5\n",
+				  ret, oldval, newval, uaddr, oparg);
+		break;
+	case FUTEX_OP_ANDN:
+		__futex_atomic_op("lr %2,%1\nnr %2,%5\n",
+				  ret, oldval, newval, uaddr, oparg);
+		break;
+	case FUTEX_OP_XOR:
+		__futex_atomic_op("lr %2,%1\nxr %2,%5\n",
+				  ret, oldval, newval, uaddr, oparg);
+		break;
+	default:
+		ret = -ENOSYS;
+	}
+	put_page(virt_to_page(uaddr));
+	*old = oldval;
+	return ret;
+}
+
+int futex_atomic_cmpxchg_pt(int __user *uaddr, int oldval, int newval)
+{
+	int ret;
+
+	spin_lock(&current->mm->page_table_lock);
+	uaddr = (int __user *) __dat_user_addr((unsigned long) uaddr);
+	if (!uaddr) {
+		spin_unlock(&current->mm->page_table_lock);
+		return -EFAULT;
+	}
+	get_page(virt_to_page(uaddr));
+	spin_unlock(&current->mm->page_table_lock);
+	asm volatile("   cs   %1,%4,0(%5)\n"
+		     "0: lr   %0,%1\n"
+		     "1:\n"
+		     EX_TABLE(0b,1b)
+		     : "=d" (ret), "+d" (oldval), "=m" (*uaddr)
+		     : "0" (-EFAULT), "d" (newval), "a" (uaddr), "m" (*uaddr)
+		     : "cc", "memory" );
+	put_page(virt_to_page(uaddr));
+	return ret;
+}
+
+struct uaccess_ops uaccess_pt = {
+	.copy_from_user		= copy_from_user_pt,
+	.copy_from_user_small	= copy_from_user_pt,
+	.copy_to_user		= copy_to_user_pt,
+	.copy_to_user_small	= copy_to_user_pt,
+	.copy_in_user		= copy_in_user_pt,
+	.clear_user		= clear_user_pt,
+	.strnlen_user		= strnlen_user_pt,
+	.strncpy_from_user	= strncpy_from_user_pt,
+	.futex_atomic_op	= futex_atomic_op_pt,
+	.futex_atomic_cmpxchg	= futex_atomic_cmpxchg_pt,
+};
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 3382e29..9ff143e 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -137,7 +137,9 @@ static int __check_access_register(struct pt_regs *regs, int error_code)
 
 /*
  * Check which address space the address belongs to.
- * Returns 1 for user space and 0 for kernel space.
+ * May return 1 or 2 for user space and 0 for kernel space.
+ * Returns 2 for user space in primary addressing mode with
+ * CONFIG_S390_EXEC_PROTECT on and kernel parameter noexec=on.
  */
 static inline int check_user_space(struct pt_regs *regs, int error_code)
 {
@@ -154,7 +156,7 @@ static inline int check_user_space(struct pt_regs *regs, int error_code)
 		return __check_access_register(regs, error_code);
 	if (descriptor == 2)
 		return current->thread.mm_segment.ar4;
-	return descriptor != 0;
+	return ((descriptor != 0) ^ (switch_amode)) << s390_noexec;
 }
 
 /*
@@ -183,6 +185,77 @@ static void do_sigsegv(struct pt_regs *regs, unsigned long error_code,
 	force_sig_info(SIGSEGV, &si, current);
 }
 
+#ifdef CONFIG_S390_EXEC_PROTECT
+extern long sys_sigreturn(struct pt_regs *regs);
+extern long sys_rt_sigreturn(struct pt_regs *regs);
+extern long sys32_sigreturn(struct pt_regs *regs);
+extern long sys32_rt_sigreturn(struct pt_regs *regs);
+
+static inline void do_sigreturn(struct mm_struct *mm, struct pt_regs *regs,
+				int rt)
+{
+	up_read(&mm->mmap_sem);
+	clear_tsk_thread_flag(current, TIF_SINGLE_STEP);
+#ifdef CONFIG_COMPAT
+	if (test_tsk_thread_flag(current, TIF_31BIT)) {
+		if (rt)
+			sys32_rt_sigreturn(regs);
+		else
+			sys32_sigreturn(regs);
+		return;
+	}
+#endif /* CONFIG_COMPAT */
+	if (rt)
+		sys_rt_sigreturn(regs);
+	else
+		sys_sigreturn(regs);
+	return;
+}
+
+static int signal_return(struct mm_struct *mm, struct pt_regs *regs,
+			 unsigned long address, unsigned long error_code)
+{
+	pgd_t *pgd;
+	pmd_t *pmd;
+	pte_t *pte;
+	u16 *instruction;
+	unsigned long pfn, uaddr = regs->psw.addr;
+
+	spin_lock(&mm->page_table_lock);
+	pgd = pgd_offset(mm, uaddr);
+	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+		goto out_fault;
+	pmd = pmd_offset(pgd, uaddr);
+	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+		goto out_fault;
+	pte = pte_offset_map(pmd_offset(pgd_offset(mm, uaddr), uaddr), uaddr);
+	if (!pte || !pte_present(*pte))
+		goto out_fault;
+	pfn = pte_pfn(*pte);
+	if (!pfn_valid(pfn))
+		goto out_fault;
+	spin_unlock(&mm->page_table_lock);
+
+	instruction = (u16 *) ((pfn << PAGE_SHIFT) + (uaddr & (PAGE_SIZE-1)));
+	if (*instruction == 0x0a77)
+		do_sigreturn(mm, regs, 0);
+	else if (*instruction == 0x0aad)
+		do_sigreturn(mm, regs, 1);
+	else {
+		printk("- XXX - do_exception: task = %s, primary, NO EXEC "
+		       "-> SIGSEGV\n", current->comm);
+		up_read(&mm->mmap_sem);
+		current->thread.prot_addr = address;
+		current->thread.trap_no = error_code;
+		do_sigsegv(regs, error_code, SEGV_MAPERR, address);
+	}
+	return 0;
+out_fault:
+	spin_unlock(&mm->page_table_lock);
+	return -EFAULT;
+}
+#endif /* CONFIG_S390_EXEC_PROTECT */
+
 /*
  * This routine handles page faults.  It determines the address,
  * and the problem, and then passes it off to one of the appropriate
@@ -260,6 +333,17 @@ do_exception(struct pt_regs *regs, unsigned long error_code, int is_protection)
         vma = find_vma(mm, address);
         if (!vma)
                 goto bad_area;
+
+#ifdef CONFIG_S390_EXEC_PROTECT
+	if (unlikely((user_address == 2) && !(vma->vm_flags & VM_EXEC)))
+		if (!signal_return(mm, regs, address, error_code))
+			/*
+			 * signal_return() has done an up_read(&mm->mmap_sem)
+			 * if it returns 0.
+			 */
+			return;
+#endif
+
         if (vma->vm_start <= address) 
                 goto good_area;
         if (!(vma->vm_flags & VM_GROWSDOWN))
diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 0e7e9ac..162a338 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -104,7 +104,7 @@ static void __init setup_ro_region(void)
 		pmd = pmd_offset(pgd, address);
 		pte = pte_offset_kernel(pmd, address);
 		new_pte = mk_pte_phys(address, __pgprot(_PAGE_RO));
-		set_pte(pte, new_pte);
+		*pte = new_pte;
 	}
 }
 
@@ -124,11 +124,11 @@ void __init paging_init(void)
 #ifdef CONFIG_64BIT
 	pgdir_k = (__pa(swapper_pg_dir) & PAGE_MASK) | _KERN_REGION_TABLE;
 	for (i = 0; i < PTRS_PER_PGD; i++)
-		pgd_clear(pg_dir + i);
+		pgd_clear_kernel(pg_dir + i);
 #else
 	pgdir_k = (__pa(swapper_pg_dir) & PAGE_MASK) | _KERNSEG_TABLE;
 	for (i = 0; i < PTRS_PER_PGD; i++)
-		pmd_clear((pmd_t *)(pg_dir + i));
+		pmd_clear_kernel((pmd_t *)(pg_dir + i));
 #endif
 	vmem_map_init();
 	setup_ro_region();
diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index cd3d93e..92a5651 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -82,7 +82,7 @@ static inline pmd_t *vmem_pmd_alloc(void)
 	if (!pmd)
 		return NULL;
 	for (i = 0; i < PTRS_PER_PMD; i++)
-		pmd_clear(pmd + i);
+		pmd_clear_kernel(pmd + i);
 	return pmd;
 }
 
@@ -97,7 +97,7 @@ static inline pte_t *vmem_pte_alloc(void)
 		return NULL;
 	pte_val(empty_pte) = _PAGE_TYPE_EMPTY;
 	for (i = 0; i < PTRS_PER_PTE; i++)
-		set_pte(pte + i, empty_pte);
+		pte[i] = empty_pte;
 	return pte;
 }
 
@@ -119,7 +119,7 @@ static int vmem_add_range(unsigned long start, unsigned long size)
 			pm_dir = vmem_pmd_alloc();
 			if (!pm_dir)
 				goto out;
-			pgd_populate(&init_mm, pg_dir, pm_dir);
+			pgd_populate_kernel(&init_mm, pg_dir, pm_dir);
 		}
 
 		pm_dir = pmd_offset(pg_dir, address);
@@ -132,7 +132,7 @@ static int vmem_add_range(unsigned long start, unsigned long size)
 
 		pt_dir = pte_offset_kernel(pm_dir, address);
 		pte = pfn_pte(address >> PAGE_SHIFT, PAGE_KERNEL);
-		set_pte(pt_dir, pte);
+		*pt_dir = pte;
 	}
 	ret = 0;
 out:
@@ -161,7 +161,7 @@ static void vmem_remove_range(unsigned long start, unsigned long size)
 		if (pmd_none(*pm_dir))
 			continue;
 		pt_dir = pte_offset_kernel(pm_dir, address);
-		set_pte(pt_dir, pte);
+		*pt_dir = pte;
 	}
 	flush_tlb_kernel_range(start, start + size);
 }
@@ -191,7 +191,7 @@ static int vmem_add_mem_map(unsigned long start, unsigned long size)
 			pm_dir = vmem_pmd_alloc();
 			if (!pm_dir)
 				goto out;
-			pgd_populate(&init_mm, pg_dir, pm_dir);
+			pgd_populate_kernel(&init_mm, pg_dir, pm_dir);
 		}
 
 		pm_dir = pmd_offset(pg_dir, address);
@@ -210,7 +210,7 @@ static int vmem_add_mem_map(unsigned long start, unsigned long size)
 			if (!new_page)
 				goto out;
 			pte = pfn_pte(new_page >> PAGE_SHIFT, PAGE_KERNEL);
-			set_pte(pt_dir, pte);
+			*pt_dir = pte;
 		}
 	}
 	ret = 0;