10 files changed, 348 insertions, 1 deletions

diff --git a/arch/x86/syscalls/syscall_32.tbl b/arch/x86/syscalls/syscall_32.tbl
index 29f9f0554f7d..7a35a6e71d44 100644
--- a/arch/x86/syscalls/syscall_32.tbl
+++ b/arch/x86/syscalls/syscall_32.tbl
@@ -355,3 +355,4 @@
 346     i386    setns                   sys_setns
 347     i386    process_vm_readv        sys_process_vm_readv            compat_sys_process_vm_readv
 348     i386    process_vm_writev       sys_process_vm_writev           compat_sys_process_vm_writev
+349     i386    kcmp                    sys_kcmp
diff --git a/arch/x86/syscalls/syscall_64.tbl b/arch/x86/syscalls/syscall_64.tbl
index dd29a9ea27c5..51171aeff0dc 100644
--- a/arch/x86/syscalls/syscall_64.tbl
+++ b/arch/x86/syscalls/syscall_64.tbl
@@ -318,6 +318,8 @@
 309     common  getcpu                  sys_getcpu
 310     64      process_vm_readv        sys_process_vm_readv
 311     64      process_vm_writev       sys_process_vm_writev
+312     64      kcmp                    sys_kcmp
+
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
 # for native 64-bit operation.
diff --git a/include/linux/kcmp.h b/include/linux/kcmp.h
new file mode 100644
index 000000000000..2dcd1b3aafc8
--- /dev/null
+++ b/include/linux/kcmp.h
@@ -0,0 +1,17 @@
+#ifndef _LINUX_KCMP_H
+#define _LINUX_KCMP_H
+
+/* Comparison type */
+enum kcmp_type {
+        KCMP_FILE,
+        KCMP_VM,
+        KCMP_FILES,
+        KCMP_FS,
+        KCMP_SIGHAND,
+        KCMP_IO,
+        KCMP_SYSVSEM,
+
+        KCMP_TYPES,
+};
+
+#endif /* _LINUX_KCMP_H */
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 3de3acb84a95..19439c75c5b2 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -858,4 +858,6 @@ asmlinkage long sys_process_vm_writev(pid_t pid,
                                       unsigned long riovcnt,
                                       unsigned long flags);
 
+asmlinkage long sys_kcmp(pid_t pid1, pid_t pid2, int type,
+                         unsigned long idx1, unsigned long idx2);
 #endif
diff --git a/kernel/Makefile b/kernel/Makefile
index 6c07f30fa9b7..80be6ca0cc75 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -25,6 +25,9 @@ endif
 obj-y += sched/
 obj-y += power/
 
+ifeq ($(CONFIG_CHECKPOINT_RESTORE),y)
+obj-$(CONFIG_X86) += kcmp.o
+endif
 obj-$(CONFIG_FREEZER) += freezer.o
 obj-$(CONFIG_PROFILING) += profile.o
 obj-$(CONFIG_STACKTRACE) += stacktrace.o
diff --git a/kernel/kcmp.c b/kernel/kcmp.c
new file mode 100644
index 000000000000..30b7b225306c
--- /dev/null
+++ b/kernel/kcmp.c
@@ -0,0 +1,196 @@
+#include <linux/kernel.h>
+#include <linux/syscalls.h>
+#include <linux/fdtable.h>
+#include <linux/string.h>
+#include <linux/random.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/errno.h>
+#include <linux/cache.h>
+#include <linux/bug.h>
+#include <linux/err.h>
+#include <linux/kcmp.h>
+
+#include <asm/unistd.h>
+
+/*
+ * We don't expose the real in-memory order of objects for security reasons.
+ * But still the comparison results should be suitable for sorting. So we
+ * obfuscate kernel pointers values and compare the production instead.
+ *
+ * The obfuscation is done in two steps. First we xor the kernel pointer with
+ * a random value, which puts pointer into a new position in a reordered space.
+ * Secondly we multiply the xor production with a large odd random number to
+ * permute its bits even more (the odd multiplier guarantees that the product
+ * is unique ever after the high bits are truncated, since any odd number is
+ * relative prime to 2^n).
+ *
+ * Note also that the obfuscation itself is invisible to userspace and if needed
+ * it can be changed to an alternate scheme.
+ */
+static unsigned long cookies[KCMP_TYPES][2] __read_mostly;
+
+static long kptr_obfuscate(long v, int type)
+{
+        return (v ^ cookies[type][0]) * cookies[type][1];
+}
+
+/*
+ * 0 - equal, i.e. v1 = v2
+ * 1 - less than, i.e. v1 < v2
+ * 2 - greater than, i.e. v1 > v2
+ * 3 - not equal but ordering unavailable (reserved for future)
+ */
+static int kcmp_ptr(void *v1, void *v2, enum kcmp_type type)
+{
+        long ret;
+
+        ret = kptr_obfuscate((long)v1, type) - kptr_obfuscate((long)v2, type);
+
+        return (ret < 0) | ((ret > 0) << 1);
+}
+
+/* The caller must have pinned the task */
+static struct file *
+get_file_raw_ptr(struct task_struct *task, unsigned int idx)
+{
+        struct file *file = NULL;
+
+        task_lock(task);
+        rcu_read_lock();
+
+        if (task->files)
+                file = fcheck_files(task->files, idx);
+
+        rcu_read_unlock();
+        task_unlock(task);
+
+        return file;
+}
+
+static void kcmp_unlock(struct mutex *m1, struct mutex *m2)
+{
+        if (likely(m2 != m1))
+                mutex_unlock(m2);
+        mutex_unlock(m1);
+}
+
+static int kcmp_lock(struct mutex *m1, struct mutex *m2)
+{
+        int err;
+
+        if (m2 > m1)
+                swap(m1, m2);
+
+        err = mutex_lock_killable(m1);
+        if (!err && likely(m1 != m2)) {
+                err = mutex_lock_killable_nested(m2, SINGLE_DEPTH_NESTING);
+                if (err)
+                        mutex_unlock(m1);
+        }
+
+        return err;
+}
+
+SYSCALL_DEFINE5(kcmp, pid_t, pid1, pid_t, pid2, int, type,
+                unsigned long, idx1, unsigned long, idx2)
+{
+        struct task_struct *task1, *task2;
+        int ret;
+
+        rcu_read_lock();
+
+        /*
+         * Tasks are looked up in caller's PID namespace only.
+         */
+        task1 = find_task_by_vpid(pid1);
+        task2 = find_task_by_vpid(pid2);
+        if (!task1 || !task2)
+                goto err_no_task;
+
+        get_task_struct(task1);
+        get_task_struct(task2);
+
+        rcu_read_unlock();
+
+        /*
+         * One should have enough rights to inspect task details.
+         */
+        ret = kcmp_lock(&task1->signal->cred_guard_mutex,
+                        &task2->signal->cred_guard_mutex);
+        if (ret)
+                goto err;
+        if (!ptrace_may_access(task1, PTRACE_MODE_READ) ||
+            !ptrace_may_access(task2, PTRACE_MODE_READ)) {
+                ret = -EPERM;
+                goto err_unlock;
+        }
+
+        switch (type) {
+        case KCMP_FILE: {
+                struct file *filp1, *filp2;
+
+                filp1 = get_file_raw_ptr(task1, idx1);
+                filp2 = get_file_raw_ptr(task2, idx2);
+
+                if (filp1 && filp2)
+                        ret = kcmp_ptr(filp1, filp2, KCMP_FILE);
+                else
+                        ret = -EBADF;
+                break;
+        }
+        case KCMP_VM:
+                ret = kcmp_ptr(task1->mm, task2->mm, KCMP_VM);
+                break;
+        case KCMP_FILES:
+                ret = kcmp_ptr(task1->files, task2->files, KCMP_FILES);
+                break;
+        case KCMP_FS:
+                ret = kcmp_ptr(task1->fs, task2->fs, KCMP_FS);
+                break;
+        case KCMP_SIGHAND:
+                ret = kcmp_ptr(task1->sighand, task2->sighand, KCMP_SIGHAND);
+                break;
+        case KCMP_IO:
+                ret = kcmp_ptr(task1->io_context, task2->io_context, KCMP_IO);
+                break;
+        case KCMP_SYSVSEM:
+#ifdef CONFIG_SYSVIPC
+                ret = kcmp_ptr(task1->sysvsem.undo_list,
+                               task2->sysvsem.undo_list,
+                               KCMP_SYSVSEM);
+#else
+                ret = -EOPNOTSUPP;
+#endif
+                break;
+        default:
+                ret = -EINVAL;
+                break;
+        }
+
+err_unlock:
+        kcmp_unlock(&task1->signal->cred_guard_mutex,
+                    &task2->signal->cred_guard_mutex);
+err:
+        put_task_struct(task1);
+        put_task_struct(task2);
+
+        return ret;
+
+err_no_task:
+        rcu_read_unlock();
+        return -ESRCH;
+}
+
+static __init int kcmp_cookies_init(void)
+{
+        int i;
+
+        get_random_bytes(cookies, sizeof(cookies));
+
+        for (i = 0; i < KCMP_TYPES; i++)
+                cookies[i][1] |= (~(~0UL >>  1) | 1);
+
+        return 0;
+}
+arch_initcall(kcmp_cookies_init);
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 47bfa16430d7..dbff751e4086 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -203,3 +203,6 @@ cond_syscall(sys_fanotify_mark);
 cond_syscall(sys_name_to_handle_at);
 cond_syscall(sys_open_by_handle_at);
 cond_syscall(compat_sys_open_by_handle_at);
+
+/* compare kernel pointers */
+cond_syscall(sys_kcmp);
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 14972017a43e..a4162e15c25f 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -1,4 +1,4 @@
-TARGETS = breakpoints mqueue vm
+TARGETS = breakpoints kcmp mqueue vm
 
 all:
         for TARGET in $(TARGETS); do \
diff --git a/tools/testing/selftests/kcmp/Makefile b/tools/testing/selftests/kcmp/Makefile
new file mode 100644
index 000000000000..dc79b86ea65c
--- /dev/null
+++ b/tools/testing/selftests/kcmp/Makefile
@@ -0,0 +1,29 @@
+uname_M := $(shell uname -m 2>/dev/null || echo not)
+ARCH ?= $(shell echo $(uname_M) | sed -e s/i.86/i386/)
+ifeq ($(ARCH),i386)
+        ARCH := X86
+        CFLAGS := -DCONFIG_X86_32 -D__i386__
+endif
+ifeq ($(ARCH),x86_64)
+        ARCH := X86
+        CFLAGS := -DCONFIG_X86_64 -D__x86_64__
+endif
+
+CFLAGS += -I../../../../arch/x86/include/generated/
+CFLAGS += -I../../../../include/
+CFLAGS += -I../../../../usr/include/
+CFLAGS += -I../../../../arch/x86/include/
+
+all:
+ifeq ($(ARCH),X86)
+        gcc $(CFLAGS) kcmp_test.c -o run_test
+else
+        echo "Not an x86 target, can't build kcmp selftest"
+endif
+
+run-tests: all
+        ./kcmp_test
+
+clean:
+        rm -fr ./run_test
+        rm -fr ./test-file
diff --git a/tools/testing/selftests/kcmp/kcmp_test.c b/tools/testing/selftests/kcmp/kcmp_test.c
new file mode 100644
index 000000000000..358cc6bfa35d
--- /dev/null
+++ b/tools/testing/selftests/kcmp/kcmp_test.c
@@ -0,0 +1,94 @@
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <limits.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <fcntl.h>
+
+#include <linux/unistd.h>
+#include <linux/kcmp.h>
+
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+
+static long sys_kcmp(int pid1, int pid2, int type, int fd1, int fd2)
+{
+        return syscall(__NR_kcmp, pid1, pid2, type, fd1, fd2);
+}
+
+int main(int argc, char **argv)
+{
+        const char kpath[] = "kcmp-test-file";
+        int pid1, pid2;
+        int fd1, fd2;
+        int status;
+
+        fd1 = open(kpath, O_RDWR | O_CREAT | O_TRUNC, 0644);
+        pid1 = getpid();
+
+        if (fd1 < 0) {
+                perror("Can't create file");
+                exit(1);
+        }
+
+        pid2 = fork();
+        if (pid2 < 0) {
+                perror("fork failed");
+                exit(1);
+        }
+
+        if (!pid2) {
+                int pid2 = getpid();
+                int ret;
+
+                fd2 = open(kpath, O_RDWR, 0644);
+                if (fd2 < 0) {
+                        perror("Can't open file");
+                        exit(1);
+                }
+
+                /* An example of output and arguments */
+                printf("pid1: %6d pid2: %6d FD: %2ld FILES: %2ld VM: %2ld "
+                       "FS: %2ld SIGHAND: %2ld IO: %2ld SYSVSEM: %2ld "
+                       "INV: %2ld\n",
+                       pid1, pid2,
+                       sys_kcmp(pid1, pid2, KCMP_FILE,          fd1, fd2),
+                       sys_kcmp(pid1, pid2, KCMP_FILES,         0, 0),
+                       sys_kcmp(pid1, pid2, KCMP_VM,            0, 0),
+                       sys_kcmp(pid1, pid2, KCMP_FS,            0, 0),
+                       sys_kcmp(pid1, pid2, KCMP_SIGHAND,       0, 0),
+                       sys_kcmp(pid1, pid2, KCMP_IO,            0, 0),
+                       sys_kcmp(pid1, pid2, KCMP_SYSVSEM,       0, 0),
+
+                        /* This one should fail */
+                       sys_kcmp(pid1, pid2, KCMP_TYPES + 1,     0, 0));
+
+                /* This one should return same fd */
+                ret = sys_kcmp(pid1, pid2, KCMP_FILE, fd1, fd1);
+                if (ret) {
+                        printf("FAIL: 0 expected but %d returned\n", ret);
+                        ret = -1;
+                } else
+                        printf("PASS: 0 returned as expected\n");
+
+                /* Compare with self */
+                ret = sys_kcmp(pid1, pid1, KCMP_VM, 0, 0);
+                if (ret) {
+                        printf("FAIL: 0 expected but %li returned\n", ret);
+                        ret = -1;
+                } else
+                        printf("PASS: 0 returned as expected\n");
+
+                exit(ret);
+        }
+
+        waitpid(pid2, &status, P_ALL);
+
+        return 0;
+}