Message-ID: <20120127191026.GL11086@moon>
Date:	Fri, 27 Jan 2012 23:10:26 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...nvz.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Andrey Vagin <avagin@...nvz.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Glauber Costa <glommer@...allels.com>,
	Andi Kleen <andi@...stfloor.org>, Tejun Heo <tj@...nel.org>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Alexey Dobriyan <adobriyan@...il.com>, Valdis.Kletnieks@...edu
Subject: Re: [RFC c/r 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v7

On Fri, Jan 27, 2012 at 10:40:54AM -0800, Eric W. Biederman wrote:
...
> 
> I believe I commented on this earlier but it looks like it got lost in
> the noise.
> 
> file == NULL != file == NULL.
> 
> When you can't lookup the file kcmp should return -EBADF.
> 

Something like below, right? (Andi I'll address your comments in
on top patch I'll make later, ok? I need to figure out where this
syscall() lives in glibc before using it).

	Cyrill
---
From: Cyrill Gorcunov <gorcunov@...nvz.org>
Subject: [RFC] syscalls, x86: Add __NR_kcmp syscall v8

While doing the checkpoint-restore in the userspace one need to determine
whether various kernel objects (like mm_struct-s of file_struct-s) are shared
between tasks and restore this state.

The 2nd step can be solved by using appropriate CLONE_ flags and the unshare
syscall, while there's currently no ways for solving the 1st one.

One of the ways for checking whether two tasks share e.g. mm_struct is to
provide some mm_struct ID of a task to its proc file, but showing such
info considered to be not that good for security reasons.

Thus after some debates we end up in conclusion that using that named
'comparision' syscall might be the best candidate. So here is it --
__NR_kcmp.

It takes up to 5 agruments - the pids of the two tasks (which
characteristics should be compared), the comparision type and
(in case of comparision of files) two file descriptors.

Lookups for pids are done in the caller's PID namespace only.

At moment only x86 is supported and tested.

Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
CC: "Eric W. Biederman" <ebiederm@...ssion.com>
CC: Pavel Emelyanov <xemul@...allels.com>
CC: Andrey Vagin <avagin@...nvz.org>
CC: KOSAKI Motohiro <kosaki.motohiro@...il.com>
CC: Ingo Molnar <mingo@...e.hu>
CC: H. Peter Anvin <hpa@...or.com>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Glauber Costa <glommer@...allels.com>
CC: Andi Kleen <andi@...stfloor.org>
CC: Tejun Heo <tj@...nel.org>
CC: Matt Helsley <matthltc@...ibm.com>
CC: Pekka Enberg <penberg@...nel.org>
CC: Eric Dumazet <eric.dumazet@...il.com>
CC: Vasiliy Kulikov <segoon@...nwall.com>
CC: Andrew Morton <akpm@...ux-foundation.org>
CC: Alexey Dobriyan <adobriyan@...il.com>
CC: Valdis.Kletnieks@...edu
---
 arch/x86/syscalls/syscall_32.tbl         |    1 
 arch/x86/syscalls/syscall_64.tbl         |    1 
 include/linux/kcmp.h                     |   17 +++
 include/linux/syscalls.h                 |    2 
 kernel/Makefile                          |    1 
 kernel/kcmp.c                            |  171 +++++++++++++++++++++++++++++++
 tools/testing/selftests/kcmp/Makefile    |   35 ++++++
 tools/testing/selftests/kcmp/kcmp_test.c |  126 ++++++++++++++++++++++
 tools/testing/selftests/run_tests        |    2 
 9 files changed, 355 insertions(+), 1 deletion(-)

Index: linux-2.6.git/arch/x86/syscalls/syscall_32.tbl
===================================================================
--- linux-2.6.git.orig/arch/x86/syscalls/syscall_32.tbl
+++ linux-2.6.git/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
Index: linux-2.6.git/arch/x86/syscalls/syscall_64.tbl
===================================================================
--- linux-2.6.git.orig/arch/x86/syscalls/syscall_64.tbl
+++ linux-2.6.git/arch/x86/syscalls/syscall_64.tbl
@@ -318,3 +318,4 @@
 309	64	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
Index: linux-2.6.git/include/linux/kcmp.h
===================================================================
--- /dev/null
+++ linux-2.6.git/include/linux/kcmp.h
@@ -0,0 +1,17 @@
+#ifndef _LINUX_KCMP_H
+#define _LINUX_KCMP_H
+
+/* Comparision type */
+enum kcmp_type {
+	KCMP_FILE,
+	KCMP_VM,
+	KCMP_FILES,
+	KCMP_FS,
+	KCMP_SIGHAND,
+	KCMP_IO,
+	KCMP_SYSVSEM,
+
+	KCMP_TYPES,
+};
+
+#endif /* _LINUX_KCMP_H */
Index: linux-2.6.git/include/linux/syscalls.h
===================================================================
--- linux-2.6.git.orig/include/linux/syscalls.h
+++ linux-2.6.git/include/linux/syscalls.h
@@ -857,4 +857,6 @@ asmlinkage long sys_process_vm_writev(pi
 				      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
Index: linux-2.6.git/kernel/Makefile
===================================================================
--- linux-2.6.git.orig/kernel/Makefile
+++ linux-2.6.git/kernel/Makefile
@@ -25,6 +25,7 @@ endif
 obj-y += sched/
 obj-y += power/
 
+obj-$(CONFIG_X86) += kcmp.o
 obj-$(CONFIG_FREEZER) += freezer.o
 obj-$(CONFIG_PROFILING) += profile.o
 obj-$(CONFIG_SYSCTL_SYSCALL_CHECK) += sysctl_check.o
Index: linux-2.6.git/kernel/kcmp.c
===================================================================
--- /dev/null
+++ linux-2.6.git/kernel/kcmp.c
@@ -0,0 +1,171 @@
+#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/cache.h>
+#include <linux/bug.h>
+#include <linux/err.h>
+#include <linux/kcmp.h>
+
+#include <asm/unistd.h>
+
+/*
+ * We don't expose real in-memory order of objects for security
+ * reasons, still the comparision results should be suitable for
+ * sorting. Thus, we obfuscate kernel pointers values (using random
+ * cookies obtaned at early boot stage) and compare the production
+ * instead.
+ */
+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
+ * 1 - less than
+ * 2 - greater than
+ * 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 fdtable *fdt;
+	struct file *file;
+
+	spin_lock(&task->files->file_lock);
+	fdt = files_fdtable(task->files);
+	if (idx < fdt->max_fds)
+		file = fdt->fd[idx];
+	else
+		file = NULL;
+	spin_unlock(&task->files->file_lock);
+
+	return file;
+}
+
+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);
+	if (!task1) {
+		rcu_read_unlock();
+		return -ESRCH;
+	}
+
+	task2 = find_task_by_vpid(pid2);
+	if (!task2) {
+		put_task_struct(task1);
+		rcu_read_unlock();
+		return -ESRCH;
+	}
+
+	get_task_struct(task1);
+	get_task_struct(task2);
+
+	rcu_read_unlock();
+
+	/*
+	 * One should have enough rights to inspect tasks details.
+	 */
+	if (!ptrace_may_access(task1, PTRACE_MODE_READ) ||
+	    !ptrace_may_access(task2, PTRACE_MODE_READ)) {
+		ret = -EACCES;
+		goto err;
+	}
+
+	/*
+	 * Note for all cases but the KCMP_FILE we
+	 * don't take any locks in a sake of speed.
+	 */
+
+	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 = -EINVAL;
+		goto err;
+#endif
+		break;
+	default:
+		ret = -EINVAL;
+		goto err;
+	}
+
+err:
+	put_task_struct(task1);
+	put_task_struct(task2);
+
+	return ret;
+}
+
+static __init int kcmp_cookie_init(void)
+{
+	int i, j;
+
+	for (i = 0; i < KCMP_TYPES; i++) {
+		for (j = 0; j < 2; j++) {
+			get_random_bytes(&cookies[i][j],
+					 sizeof(cookies[i][j]));
+		}
+		cookies[i][1] |= (~(~0UL >>  1) | 1);
+	}
+
+	return 0;
+}
+late_initcall(kcmp_cookie_init);
Index: linux-2.6.git/tools/testing/selftests/kcmp/Makefile
===================================================================
--- /dev/null
+++ linux-2.6.git/tools/testing/selftests/kcmp/Makefile
@@ -0,0 +1,35 @@
+ifeq ($(strip $(V)),)
+	E = @echo
+	Q = @
+else
+	E = @\#
+	Q =
+endif
+export E Q
+
+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
+endif
+ifeq ($(ARCH),x86_64)
+	ARCH := X86
+	CFLAGS := -DCONFIG_X86_64
+endif
+
+CFLAGS += -I../../../../arch/x86/include/generated/
+CFLAGS += -I../../../../include/
+
+all:
+ifeq ($(ARCH),X86)
+	$(E) "  CC run_test"
+	$(Q) gcc $(CFLAGS) kcmp_test.c -o run_test
+else
+	$(E) "Not an x86 target, can't build breakpoints selftests"
+endif
+
+clean:
+	$(E) "  CLEAN"
+	$(Q) rm -fr ./run_test
+	$(Q) rm -fr ./test-file
Index: linux-2.6.git/tools/testing/selftests/kcmp/kcmp_test.c
===================================================================
--- /dev/null
+++ linux-2.6.git/tools/testing/selftests/kcmp/kcmp_test.c
@@ -0,0 +1,126 @@
+#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 <sys/types.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+
+#ifdef CONFIG_X86_64
+#include "asm/unistd_64.h"
+#else
+#include "asm/unistd_32.h"
+#endif
+
+#include "linux/kcmp.h"
+
+#ifdef CONFIG_X86_64
+static long syscall5(int nr, unsigned long arg0, unsigned long arg1,
+		unsigned long arg2, unsigned long arg3,
+		unsigned long arg4)
+{
+	long ret;
+	asm volatile(
+		"movl %1, %%eax		\n"
+		"movq %2, %%rdi		\n"
+		"movq %3, %%rsi		\n"
+		"movq %4, %%rdx		\n"
+		"movq %5, %%r10		\n"
+		"movq %6, %%r8		\n"
+		"syscall		\n"
+		"movq %%rax, %0		\n"
+		: "=r"(ret)
+		: "g" ((int)nr), "g" (arg0), "g" (arg1), "g" (arg2),
+			"g" (arg3), "g" (arg4)
+		: "rax", "rdi", "rsi", "rdx", "r10", "r8", "memory");
+	return ret;
+}
+#else
+static long syscall5(int nr, unsigned long arg0, unsigned long arg1,
+		unsigned long arg2, unsigned long arg3,
+		unsigned long arg4)
+{
+	long ret;
+	asm volatile(
+		"movl %1, %%eax		\n"
+		"movl %2, %%ebx		\n"
+		"movl %3, %%ecx		\n"
+		"movl %4, %%edx		\n"
+		"movl %5, %%esi		\n"
+		"movl %6, %%edi		\n"
+		"intl $0x80		\n"
+		"movq %%eax, %0		\n"
+		: "=r"(ret)
+		: "g" ((int)nr), "g" (arg0), "g" (arg1), "g" (arg2),
+			"g" (arg3), "g" (arg4)
+		: "eax", "ebx", "ecx", "edx", "esi", "edi", "memory");
+	return ret;
+}
+#endif
+
+static long sys_kcmp(int pid1, int pid2, int type, int fd1, int fd2)
+{
+	return syscall5(__NR_kcmp, (long)pid1, (long)pid2,
+			(long)type, (long)fd1, (long)fd2);
+}
+
+int main(int argc, char **argv)
+{
+	int pid1, pid2;
+	int fd1, fd2;
+	int status;
+
+	fd1 = open("test-file", 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();
+
+		fd2 = open("test-file", O_RDWR, 0644);
+		if (fd2 < 0) {
+			perror("Can't open file");
+			exit(1);
+		}
+
+                printf("pid1: %6d pid2: %6d FD: %2d FILES: %2d VM: %2d FS: %2d "
+		       "SIGHAND: %2d IO: %2d SYSVSEM: %2d INV: %2d\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 */
+		printf("pid1: %6d pid2: %6d SAME-FD: %2d\n",
+		       pid1, pid2,
+		       sys_kcmp(pid1, pid2, KCMP_FILE,		fd1, fd1));
+
+		exit(0);
+	}
+
+	waitpid(pid2, &status, P_ALL);
+
+	return 0;
+}
Index: linux-2.6.git/tools/testing/selftests/run_tests
===================================================================
--- linux-2.6.git.orig/tools/testing/selftests/run_tests
+++ linux-2.6.git/tools/testing/selftests/run_tests
@@ -1,6 +1,6 @@
 #!/bin/bash
 
-TARGETS=breakpoints
+TARGETS="breakpoints kcmp"
 
 for TARGET in $TARGETS
 do
--
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