Messages in this thread Patch in this message | | | Date | Mon, 12 Dec 2011 13:53:23 -0800 | From | Andrew Morton <> | Subject | Re: [patch 3/3] [PATCH] prctl: Add PR_SET_MM codes to set up mm_struct entires v3 |
| |
On Tue, 13 Dec 2011 00:51:14 +0400 Cyrill Gorcunov <gorcunov@gmail.com> wrote:
> > When we restore a task we need to set up text, data and data > heap sizes from userspace to the values a task had at > checkpoint time. This patch adds auxilary prctl codes for that. > > While most of them have a statistical nature (their values > are involved into calculation of /proc/<pid>/statm output) > the start_brk and brk values are used to compute an allowed > size of program data segment expansion. Which means an arbitrary > changes of this values might be dangerous operation. So to restrict > access the following requirements applied to prctl calls: > > - The process has to have CAP_SYS_ADMIN capability granted. > - For all opcodes except start_brk/brk members an appropriate > VMA area must exist and should fit certain VMA flags, > such as: > - code segment must be executable but not writable; > - data segment must not be executable. > > start_brk/brk values must not intersect with data segment > and must not exceed RLIMIT_DATA resource limit. > > Still the main guard is CAP_SYS_ADMIN capability check. > > Note the kernel should be compiled with CONFIG_CHECKPOINT_RESTORE > support otherwise these prctl calls will return -EINVAL. > > ... > > +#ifdef CONFIG_CHECKPOINT_RESTORE > +static int prctl_set_mm(int opt, unsigned long addr, > + unsigned long arg4, unsigned long arg5) > +{ > + unsigned long rlim = rlimit(RLIMIT_DATA); > + unsigned long vm_req_flags; > + unsigned long vm_bad_flags; > + struct vm_area_struct *vma; > + int error = 0; > + > + if (arg4 | arg5) > + return -EINVAL; > + > + if (!capable(CAP_SYS_ADMIN)) > + return -EPERM; > + > + if (addr >= TASK_SIZE) > + return -EINVAL; > + > + down_read(¤t->mm->mmap_sem);
This may not be true of all compiler versions, but when I cache current->mm in a local, the code size is reduced rather a lot:
akpm:/usr/src/25> size kernel/sys.o text data bss dec hex filename 22685 14376 7616 44677 ae85 kernel/sys.o 22489 14376 7616 44481 adc1 kernel/sys.o
diff -puN kernel/sys.c~c-r-prctl-add-pr_set_mm-codes-to-set-up-mm_struct-entries-fix kernel/sys.c --- a/kernel/sys.c~c-r-prctl-add-pr_set_mm-codes-to-set-up-mm_struct-entries-fix +++ a/kernel/sys.c @@ -1701,6 +1701,7 @@ static int prctl_set_mm(int opt, unsigne unsigned long vm_bad_flags; struct vm_area_struct *vma; int error = 0; + struct mm_struct *mm = current->mm; if (arg4 | arg5) return -EINVAL; @@ -1711,8 +1712,8 @@ static int prctl_set_mm(int opt, unsigne if (addr >= TASK_SIZE) return -EINVAL; - down_read(¤t->mm->mmap_sem); - vma = find_vma(current->mm, addr); + down_read(&mm->mmap_sem); + vma = find_vma(mm, addr); if (opt != PR_SET_MM_START_BRK && opt != PR_SET_MM_BRK) { /* It must be existing VMA */ @@ -1732,9 +1733,9 @@ static int prctl_set_mm(int opt, unsigne goto out; if (opt == PR_SET_MM_START_CODE) - current->mm->start_code = addr; + mm->start_code = addr; else - current->mm->end_code = addr; + mm->end_code = addr; break; case PR_SET_MM_START_DATA: @@ -1747,9 +1748,9 @@ static int prctl_set_mm(int opt, unsigne goto out; if (opt == PR_SET_MM_START_DATA) - current->mm->start_data = addr; + mm->start_data = addr; else - current->mm->end_data = addr; + mm->end_data = addr; break; case PR_SET_MM_START_STACK: @@ -1762,31 +1763,31 @@ static int prctl_set_mm(int opt, unsigne if ((vma->vm_flags & vm_req_flags) != vm_req_flags) goto out; - current->mm->start_stack = addr; + mm->start_stack = addr; break; case PR_SET_MM_START_BRK: - if (addr <= current->mm->end_data) + if (addr <= mm->end_data) goto out; if (rlim < RLIM_INFINITY && - (current->mm->brk - addr) + - (current->mm->end_data - current->mm->start_data) > rlim) + (mm->brk - addr) + + (mm->end_data - mm->start_data) > rlim) goto out; - current->mm->start_brk = addr; + mm->start_brk = addr; break; case PR_SET_MM_BRK: - if (addr <= current->mm->end_data) + if (addr <= mm->end_data) goto out; if (rlim < RLIM_INFINITY && - (addr - current->mm->start_brk) + - (current->mm->end_data - current->mm->start_data) > rlim) + (addr - mm->start_brk) + + (mm->end_data - mm->start_data) > rlim) goto out; - current->mm->brk = addr; + mm->brk = addr; break; default: @@ -1797,7 +1798,7 @@ static int prctl_set_mm(int opt, unsigne error = 0; out: - up_read(¤t->mm->mmap_sem); + up_read(&mm->mmap_sem); return error; } _
| |