Understanding proc_rwmem

[Kostik Belousov]

On Wed, Apr 14, 2010 at 05:21:00PM -0400, John Baldwin wrote:
> On Wednesday 14 April 2010 4:22:56 pm Fernando Apestegu?a wrote:
> > Hi all,
> > 
> > I'm trying to read process memory other than the current process in
> > kernel. I was told to use the proc_rwmem function, however I can't get
> > it working properly. At first, I'm trying to read how many elements
> > the environment variables vector has. To do this I tried this from a
> > linprocfs filler function:
> > 
> > 
> >         struct iovec iov;
> > 	struct uio tmp_uio;
> > 	struct ps_strings *pss;
> > 	int ret_code;
> > 
> > 	buff = malloc(sizeof(struct ps_strings), M_TEMP, M_WAITOK);
> > 	memset(buff, 0, sizeof(struct ps_strings));
> > 
> > 	PROC_LOCK_ASSERT(td->td_proc, MA_NOTOWNED);
> > 	iov.iov_base = (caddr_t) buff;
> > 	iov.iov_len = sizeof(struct ps_strings);
> > 	tmp_uio.uio_iov = &iov;
> > 	tmp_uio.uio_iovcnt = 1;
> > 	tmp_uio.uio_offset = (off_t)(p->p_sysent->sv_psstrings);
> > 	tmp_uio.uio_resid = sizeof(struct ps_strings);
> > 	tmp_uio.uio_segflg = UIO_USERSPACE;
> > 	tmp_uio.uio_rw = UIO_READ;
> > 	tmp_uio.uio_td = td;
> > 	ret_code = proc_rwmem(td->td_proc, &tmp_uio);
> 
> I think you want to use 'p' instead of 'td->td_proc' here.  As it is you are 
> reading from the current process instead of the target process I believe.

And UIO_USERSPACE sound suspicious. Note that segment flag
is for the requestor address space.
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