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    SubjectRe: [RFC PATCH 3/5] mm: introduce VM_EXEC_KEEP
    Anthony Yznaga <anthony.yznaga@oracle.com> writes:

    > A vma with the VM_EXEC_KEEP flag is preserved across exec. For anonymous
    > vmas only. For safety, overlap with fixed address VMAs created in the new
    > mm during exec (e.g. the stack and elf load segments) is not permitted and
    > will cause the exec to fail.
    > (We are studying how to guarantee there are no conflicts. Comments welcome.)
    >

    > diff --git a/fs/exec.c b/fs/exec.c
    > index 262112e5f9f8..1de09c4eef00 100644
    > --- a/fs/exec.c
    > +++ b/fs/exec.c
    > @@ -1069,6 +1069,20 @@ ssize_t read_code(struct file *file, unsigned long addr, loff_t pos, size_t len)
    > EXPORT_SYMBOL(read_code);
    > #endif
    >
    > +static int vma_dup_some(struct mm_struct *old_mm, struct mm_struct *new_mm)
    > +{
    > + struct vm_area_struct *vma;
    > + int ret;
    > +
    > + for (vma = old_mm->mmap; vma; vma = vma->vm_next)
    > + if (vma->vm_flags & VM_EXEC_KEEP) {
    > + ret = vma_dup(vma, new_mm);
    > + if (ret)
    > + return ret;
    > + }
    > + return 0;
    > +}
    > +
    > /*
    > * Maps the mm_struct mm into the current task struct.
    > * On success, this function returns with the mutex
    > @@ -1104,6 +1118,12 @@ static int exec_mmap(struct mm_struct *mm)
    > mutex_unlock(&tsk->signal->exec_update_mutex);
    > return -EINTR;
    > }
    > + ret = vma_dup_some(old_mm, mm);
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    Ouch! An unconditional loop through all of the vmas of the execing
    process, just in case there is a VM_EXEC_KEEP vma.

    I know we already walk the list in exit_mmap, but I get the feeling this
    will slow exec down when this feature is not enabled, especially when
    a process with a lot of vmas is calling exec.


    > + if (ret) {
    > + mmap_read_unlock(old_mm);
    > + mutex_unlock(&tsk->signal->exec_update_mutex);
    > + return ret;
    > + }
    > }
    >
    > task_lock(tsk);

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