lkml.org 
[lkml]   [2012]   [Jan]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [patch 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v4
Date
Cyrill Gorcunov <gorcunov@gmail.com> writes:

> On Tue, Jan 24, 2012 at 12:44:59PM -0800, Eric W. Biederman wrote:
>> Cyrill Gorcunov <gorcunov@gmail.com> writes:
>>
>> > On Tue, Jan 24, 2012 at 03:20:26PM -0500, KOSAKI Motohiro wrote:
>> >> >> please do as you like.
>> >> >
>> >> > So it should be something like below I think...
>> >>
>> >> Looks ok this version to me. So, if you fix other developers pointed
>> >> issue, I'll ack this.
>> >>
>> >
>> > Thanks!
>> >
>> > Eric, so mm/ would be fine or I still should move it to kernel/
>> > instead? I've addressed other issues I hope.
>>
>> The world won't fall apart if the code lands in mm. I have a strong
>> preference for kernel/. I just don't see anything at all memory
>> management like about that code. Even the fact that you are
>> comparing pointers is an implementation detail.
>
> This one should fit all requirements I guess.

Bahahaha!

Looking I see one more nit.

You need an entry in include/linux/syscalls.h

Eric

> ---
> From: Cyrill Gorcunov <gorcunov@openvz.org>
> Subject: [RFC] syscalls, x86: Add __NR_kcmp syscall v6
>
> 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.
>
> At moment only x86 is supported.
>
> Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
> CC: "Eric W. Biederman" <ebiederm@xmission.com>
> CC: Pavel Emelyanov <xemul@parallels.com>
> CC: Andrey Vagin <avagin@openvz.org>
> CC: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
> CC: Ingo Molnar <mingo@elte.hu>
> CC: H. Peter Anvin <hpa@zytor.com>
> CC: Thomas Gleixner <tglx@linutronix.de>
> CC: Glauber Costa <glommer@parallels.com>
> CC: Andi Kleen <andi@firstfloor.org>
> CC: Tejun Heo <tj@kernel.org>
> CC: Matt Helsley <matthltc@us.ibm.com>
> CC: Pekka Enberg <penberg@kernel.org>
> CC: Eric Dumazet <eric.dumazet@gmail.com>
> CC: Vasiliy Kulikov <segoon@openwall.com>
> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: Alexey Dobriyan <adobriyan@gmail.com>
> CC: Valdis.Kletnieks@vt.edu
> ---
> arch/x86/include/asm/syscalls.h | 4
> arch/x86/syscalls/syscall_32.tbl | 1
> arch/x86/syscalls/syscall_64.tbl | 1
> include/linux/kcmp.h | 17 ++++
> kernel/Makefile | 1
> kernel/kcmp.c | 163 +++++++++++++++++++++++++++++++++++++++
> 6 files changed, 187 insertions(+)
>
> Index: linux-2.6.git/arch/x86/include/asm/syscalls.h
> ===================================================================
> --- linux-2.6.git.orig/arch/x86/include/asm/syscalls.h
> +++ linux-2.6.git/arch/x86/include/asm/syscalls.h
> @@ -42,6 +42,10 @@ long sys_sigaltstack(const stack_t __use
> asmlinkage int sys_set_thread_area(struct user_desc __user *);
> asmlinkage int sys_get_thread_area(struct user_desc __user *);
>
> +/* kernel/kcmp.c */
> +asmlinkage long sys_kcmp(pid_t pid1, pid_t pid2, int type,
> + unsigned long idx1, unsigned long idx2);
> +
> /* X86_32 only */
> #ifdef CONFIG_X86_32
>
> 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_FILE,
> + KCMP_VM,
> + KCMP_FILES,
> + KCMP_FS,
> + KCMP_SIGHAND,
> + KCMP_IO,
> + KCMP_SYSVSEM,
> +
> + KCMP_TYPES,
> +};
> +
> +#endif /* _LINUX_KCMP_H */
> 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 +1,163 @@
> +#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>
> +
> +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
> + */
> +static int kcmp_ptr(long v1, long v2, int type)
> +{
> + long ret;
> +
> + ret = kptr_obfuscate(v1, type) - kptr_obfuscate(v2, type);
> +
> + return (ret < 0) | ((ret > 0) << 1);
> +}
> +
> +#define KCMP_TASK_PTR(task1, task2, member, type) \
> + kcmp_ptr((long)(task1)->member, \
> + (long)(task2)->member, \
> + type)
> +
> +#define KCMP_PTR(ptr1, ptr2, type) \
> + kcmp_ptr((long)ptr1, (long)ptr2, type)
> +
> +/* A caller must be sure the task is presented in memory */
> +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;
> + struct task_struct *task2;
> + int ret = 0;
> +
> + rcu_read_lock();
> +
> + 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();
> +
> + 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 = -ENOENT;
> + break;
> + }
> + case KCMP_VM:
> + ret = KCMP_TASK_PTR(task1, task2, mm, KCMP_VM);
> + break;
> + case KCMP_FILES:
> + ret = KCMP_TASK_PTR(task1, task2, files, KCMP_FILES);
> + break;
> + case KCMP_FS:
> + ret = KCMP_TASK_PTR(task1, task2, fs, KCMP_FS);
> + break;
> + case KCMP_SIGHAND:
> + ret = KCMP_TASK_PTR(task1, task2, sighand, KCMP_SIGHAND);
> + break;
> + case KCMP_IO:
> + ret = KCMP_TASK_PTR(task1, task2, io_context, KCMP_IO);
> + break;
> + case KCMP_SYSVSEM:
> +#ifdef CONFIG_SYSVIPC
> + ret = KCMP_TASK_PTR(task1, task2, sysvsem.undo_list, KCMP_SYSVSEM);
> +#else
> + ret = -ENOENT;
> + 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);


\
 
 \ /
  Last update: 2012-01-24 22:19    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site