[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>

9 files changed, 111 insertions, 48 deletions

diff --git a/arch/s390/kernel/compat_linux.c b/arch/s390/kernel/compat_linux.c
index cf84d697daed..666bb6daa148 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 1a18e29668ef..e89f8c0c42a0 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 8d17b2ab6f21..887a9881d0d0 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 9e9972e8a52b..2c91226e1d40 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 6603fbb41d07..5acfac654f9d 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 29fde70090fe..2a8f0872ea8b 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 25bf7277d311..b1b9a931237d 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 4c8a7954ef48..554f9cf7499c 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 3cb7e1032072..cb155d9fd749 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;