Fix security holes in sigreturn(), ptrace() and procfs. sigreturn()

attempted to check for insecure and fatal eflags and segment
selectors, but missed many cases and got the IOPL check back to
front.  The other syscalls didn't check at all.

sys_process.c, machdep.c:
Only allow PT_WRITE_U to write to the registers (ordinary and FP).

psl.h, locore.s, machdep.c:
Eliminate PSL_MBZ, PSL_MBO and PSL_USERCLR.  We are not supposed
to assume anything about the reserved bits.  Use PSL_USERCHANGE
and PSL_KERNEL instead.  Rename PSL_USERSET to PSL_USER.

exception.s:
Define a private label for use by doreti when returning to user
mode fails.

machdep.c:
In syscalls, allow changing only the eflags that can be changed on
486's in user mode (no longer attempt to allow benign IOPL changes;
allow changing the nasty PSL_NT; don't allow changing the i586
bits).

Don't attempt to check all the cases involving invalid selectors
and %eip's.  Just check for privilege violations and let the invalid
things cause a trap.

procfs_machdep.c:
Call the ptrace register functions to do all the work for reading
and writing ordinary registers and for single stepping.

trap.c:
Ignore traps caused by PSL_NT being set.  Previously, users could
cause a fatal trap in user mode by setting PSL_NT and executing an
iret, and a fatal trap in kernel mode by setting PSL_NT and making
a syscall.  PSL_NT was cleared too late and not in enough modes to
fix the problem.

Make all traps in user mode (except T_NMI) nonfatal.

Recover from traps caused by attempting to load invalid user
registers in doreti by restarting the traps so that they appear to
occur in user mode.
---

Fix bogons that I noticed while fixing the above:

psl.h:
Fix some comments.

Uniformize idempotency ifdef.

exception.s, machdep.c:
Remove rsvd[0-14].  rsvd0 hasn't been reserved since the 486 came
out.  Replace rsvd0 by `align'.  rsvd[0-11] used wrong (magic
non-unique) trap numbers.  Replace rsvd[1-14] by rsvd.

locore.s:
Enable alignment check flag on 486's and 586's.

machdep.c:
Use a better type for kstack[].

Use TFREGP() to find the registers.

Reformat ptrace functions from SEF to something closer to KNF.

procfs_machdep.c:
The wrong pointer to the registers got fixed as a side effect.

Implement reading and writing of FP registers.

/proc/*/*regs now work (only) for processes that are in memory.

Clean up comments.

trap.c, trap.h:
Remove unused trap types.

1 files changed, 2 insertions, 6 deletions

diff --git a/sys/kern/sys_process.c b/sys/kern/sys_process.c
index 63537bd..692f2c5 100644
--- a/sys/kern/sys_process.c
+++ b/sys/kern/sys_process.c
@@ -28,7 +28,7 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	$Id: sys_process.c,v 1.6 1994/08/18 22:35:05 wollman Exp $
+ *	$Id: sys_process.c,v 1.7 1994/09/25 19:33:49 phk Exp $
  */
 
 #include <sys/param.h>
@@ -326,13 +326,9 @@ ptrace(curp, uap, retval)
 		*retval = *(int*)((u_int)p->p_addr + (u_int)uap->addr);
 		return 0;
 	case PT_WRITE_U:
-		if ((u_int)uap->addr > (UPAGES * NBPG - sizeof(int))) {
-			return EFAULT;
-		}
 		p->p_addr->u_kproc.kp_proc = *p;
 		fill_eproc (p, &p->p_addr->u_kproc.kp_eproc);
-		*(int*)((u_int)p->p_addr + (u_int)uap->addr) = uap->data;
-		return 0;
+		return ptrace_write_u(p, (vm_offset_t)uap->addr, uap->data);
 	case PT_KILL:
 		p->p_xstat = SIGKILL;
 		setrunnable(p);