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Date: Tue, 24 Jan 2012 11:16:55 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Cyrill Gorcunov <gorcunov@...nvz.org>
Cc: linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Pavel Emelyanov <xemul@...allels.com>,
Serge Hallyn <serge.hallyn@...onical.com>,
Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>,
Andrew Vagin <avagin@...nvz.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Alexey Dobriyan <adobriyan@...il.com>,
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>,
Matt Helsley <matthltc@...ibm.com>,
Pekka Enberg <penberg@...nel.org>,
Eric Dumazet <eric.dumazet@...il.com>,
Vasiliy Kulikov <segoon@...nwall.com>, Valdis.Kletnieks@...edu
Subject: Re: [patch 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v4
On Mon, 23 Jan 2012 18:20:38 +0400
Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
> 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@...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/include/asm/kcmp.h | 17 ++++
> arch/x86/include/asm/syscalls.h | 4
> arch/x86/kernel/Makefile | 1
> arch/x86/kernel/kcmp.c | 163 +++++++++++++++++++++++++++++++++++++++
> arch/x86/syscalls/syscall_32.tbl | 1
> arch/x86/syscalls/syscall_64.tbl | 1
> 6 files changed, 187 insertions(+)
>
> Index: linux-2.6.git/arch/x86/include/asm/kcmp.h
> ===================================================================
> --- /dev/null
> +++ linux-2.6.git/arch/x86/include/asm/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 */
Why under /arch ?
> 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 *);
>
> +/* kenrel/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/kernel/Makefile
> ===================================================================
> --- linux-2.6.git.orig/arch/x86/kernel/Makefile
> +++ linux-2.6.git/arch/x86/kernel/Makefile
> @@ -34,6 +34,7 @@ obj-y += alternative.o i8253.o pci-nom
> obj-y += tsc.o io_delay.o rtc.o
> obj-y += pci-iommu_table.o
> obj-y += resource.o
> +obj-y += kcmp.o
>
> obj-y += trampoline.o trampoline_$(BITS).o
> obj-y += process.o
> Index: linux-2.6.git/arch/x86/kernel/kcmp.c
> ===================================================================
> --- /dev/null
> +++ linux-2.6.git/arch/x86/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 <asm/unistd.h>
> +#include <asm/kcmp.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];
> +}
> +
I'm sorry could you add comments to swho what this does ?
> +/*
> + * 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;
> +}
It seems this function itself doesn't depend on arch.
Thanks,
-Kame
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