Re: [PATCH 1/2] mm/madvise: introduce PR_MADV_SELF flag to process_madvise()

[Lorenzo Stoakes]

On Mon, Sep 23, 2024 at 11:56:06AM GMT, Shakeel Butt wrote:
> On Mon, Sep 23, 2024 at 05:03:56PM GMT, Lorenzo Stoakes wrote:
> [...]
> >  SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
> >  		size_t, vlen, int, behavior, unsigned int, flags)
> >  {
> > @@ -1486,10 +1509,9 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
> >  	struct iov_iter iter;
> >  	struct task_struct *task;
> >  	struct mm_struct *mm;
> > -	size_t total_len;
> >  	unsigned int f_flags;
> >
> > -	if (flags != 0) {
> > +	if (flags & ~PR_MADV_SELF) {
> >  		ret = -EINVAL;
> >  		goto out;
> >  	}
> > @@ -1498,13 +1520,26 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
> >  	if (ret < 0)
> >  		goto out;
> >
> > +	/*
> > +	 * Perform an madvise operation on the current process. No restrictions
> > +	 * need be applied, nor do we need to pin the task or mm_struct.
> > +	 */
> > +	if (flags & PR_MADV_SELF) {
> > +		ret = vector_madvise(current->mm, &iter, behavior);
> > +		goto free_iov;
> > +	}
> > +
> >  	task = pidfd_get_task(pidfd, &f_flags);
> >  	if (IS_ERR(task)) {
> >  		ret = PTR_ERR(task);
> >  		goto free_iov;
> >  	}
> >
> > -	if (!process_madvise_behavior_valid(behavior)) {
> > +	/*
> > +	 * We need only perform this check if we are attempting to manipulate a
> > +	 * remote process's address space.
> > +	 */
> > +	if (mm != current->mm && !process_madvise_remote_valid(behavior)) {
>
> Move the above check after mm is initialized i.e. mm = mm_access().
>
> Shakeel

Ugh, sorry silly one there! Reflexively put that check in the original position.

Enclose a quick fix-patch for it, will fix on any respin also.

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