Understanding proc_rwmem

[Fernando Apesteguía]

On Wed, Apr 14, 2010 at 11:35 PM, Kostik Belousov <kostikbel at gmail.com> wrote:
> 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.

Ugh, sorry. Copy-paste error. Yes, that should be UIO_SYSSPACE.

>