Close the remaining user address mapping races for physical

I/O, CAM, and AIO.  Still TODO: streamline useracc() checks.

Reviewed by:	alc, tegge
MFC after:	7 days

sys/cam/cam_periph.c

@@ -534,7 +534,7 @@ cam_periph_unlock(struct cam_periph *periph)
 int
 cam_periph_mapmem(union ccb *ccb, struct cam_periph_map_info *mapinfo)
 {
-	int numbufs, i;
+	int numbufs, i, j;
 	int flags[CAM_PERIPH_MAXMAPS];
 	u_int8_t **data_ptrs[CAM_PERIPH_MAXMAPS];
 	u_int32_t lengths[CAM_PERIPH_MAXMAPS];
@@ -659,8 +659,28 @@ cam_periph_mapmem(union ccb *ccb, struct cam_periph_map_info *mapinfo)
 		/* set the direction */
 		mapinfo->bp[i]->b_iocmd = flags[i];
 
-		/* map the buffer into kernel memory */
-		vmapbuf(mapinfo->bp[i]);
+		/*
+		 * Map the buffer into kernel memory.
+		 *
+		 * Note that useracc() alone is not a  sufficient test.
+		 * vmapbuf() can still fail due to a smaller file mapped
+		 * into a larger area of VM, or if userland races against
+		 * vmapbuf() after the useracc() check.
+		 */
+		if (vmapbuf(mapinfo->bp[i]) < 0) {
+			printf("cam_periph_mapmem: error, "
+				"address %p, length %lu isn't "
+				"user accessible any more\n",
+				(void *)*data_ptrs[i],
+				(u_long)lengths[i]);
+			for (j = 0; j < i; ++j) {
+				*data_ptrs[j] = mapinfo->bp[j]->b_saveaddr;
+				mapinfo->bp[j]->b_flags &= ~B_PHYS;
+				relpbuf(mapinfo->bp[j], NULL);
+			}
+			PRELE(curproc);
+			return(EACCES);
+		}
 
 		/* set our pointer to the new mapped area */
 		*data_ptrs[i] = mapinfo->bp[i]->b_data;

sys/kern/kern_physio.c

@@ -95,13 +95,23 @@ physio(dev_t dev, struct uio *uio, int ioflag)
 			bp->b_blkno = btodb(bp->b_offset);
 
 			if (uio->uio_segflg == UIO_USERSPACE) {
+				/*
+				 * Note that useracc() alone is not a
+				 * sufficient test.  vmapbuf() can still fail
+				 * due to a smaller file mapped into a larger
+				 * area of VM, or if userland races against
+				 * vmapbuf() after the useracc() check.
+				 */
 				if (!useracc(bp->b_data, bp->b_bufsize,
 				    bp->b_iocmd == BIO_READ ?
 				    VM_PROT_WRITE : VM_PROT_READ)) {
 					error = EFAULT;
 					goto doerror;
 				}
-				vmapbuf(bp);
+				if (vmapbuf(bp) < 0) {
+					error = EFAULT;
+					goto doerror;
+				}
 			}
 
 			DEV_STRATEGY(bp);

sys/kern/vfs_aio.c

@@ -1124,8 +1124,19 @@ aio_qphysio(struct proc *p, struct aiocblist *aiocbe)
 		}
 	}
 
-	/* Bring buffer into kernel space. */
-	vmapbuf(bp);
+	/*
+	 * Bring buffer into kernel space.
+	 *
+	 * Note that useracc() alone is not a 
+	 * sufficient test.  vmapbuf() can still fail
+	 * due to a smaller file mapped into a larger
+	 * area of VM, or if userland races against
+	 * vmapbuf() after the useracc() check.
+	 */
+	if (vmapbuf(bp) < 0) {
+		error = EFAULT;
+		goto doerror;
+	}
 
 	s = splbio();
 	aiocbe->bp = bp;

sys/kern/vfs_bio.c

@@ -3547,13 +3547,18 @@ vm_hold_free_pages(struct buf * bp, vm_offset_t from, vm_offset_t to)
  * All requests are (re)mapped into kernel VA space.
  * Notice that we use b_bufsize for the size of the buffer
  * to be mapped.  b_bcount might be modified by the driver.
+ *
+ * Note that even if the caller determines that the address space should
+ * be valid, a race or a smaller-file mapped into a larger space may
+ * actually cause vmapbuf() to fail, so all callers of vmapbuf() MUST
+ * check the return value.
  */
-void
+int
 vmapbuf(struct buf *bp)
 {
 	caddr_t addr, kva;
 	vm_offset_t pa;
-	int pidx;
+	int pidx, i;
 	struct vm_page *m;
 	struct pmap *pmap = &curproc->p_vmspace->vm_pmap;
 
@@ -3573,11 +3578,25 @@ vmapbuf(struct buf *bp)
 		 * the userland address space, and kextract is only guarenteed
 		 * to work for the kernland address space (see: sparc64 port).
 		 */
-		vm_fault_quick((addr >= bp->b_data) ? addr : bp->b_data,
-			(bp->b_iocmd == BIO_READ)?(VM_PROT_READ|VM_PROT_WRITE):VM_PROT_READ);
+retry:
+		i = vm_fault_quick((addr >= bp->b_data) ? addr : bp->b_data,
+			(bp->b_iocmd == BIO_READ) ?
+			(VM_PROT_READ|VM_PROT_WRITE) : VM_PROT_READ);
+		if (i < 0) {
+			printf("vmapbuf: warning, bad user address during I/O\n");
+			vm_page_lock_queues();
+			for (i = 0; i < pidx; ++i) {
+				vm_page_unhold(bp->b_pages[i]);
+				bp->b_pages[i] = NULL;
+			}
+			vm_page_unlock_queues();
+			return(-1);
+		}
 		pa = trunc_page(pmap_extract(pmap, (vm_offset_t) addr));
-		if (pa == 0)
-			panic("vmapbuf: page not present");
+		if (pa == 0) {
+			printf("vmapbuf: warning, race against user address during I/O");
+			goto retry;
+		}
 		m = PHYS_TO_VM_PAGE(pa);
 		vm_page_lock_queues();
 		vm_page_hold(m);
@@ -3592,6 +3611,7 @@ vmapbuf(struct buf *bp)
 	bp->b_npages = pidx;
 	bp->b_saveaddr = bp->b_data;
 	bp->b_data = kva + (((vm_offset_t) bp->b_data) & PAGE_MASK);
+	return(0);
 }
 
 /*

sys/sys/buf.h

@@ -499,7 +499,7 @@ void	vfs_bio_clrbuf(struct buf *);
 void	vfs_busy_pages(struct buf *, int clear_modify);
 void	vfs_unbusy_pages(struct buf *);
 void	vwakeup(struct buf *);
-void	vmapbuf(struct buf *);
+int	vmapbuf(struct buf *);
 void	vunmapbuf(struct buf *);
 void	relpbuf(struct buf *, int *);
 void	brelvp(struct buf *);

sys/vm/vm_glue.c

@@ -121,6 +121,12 @@ static void vm_proc_swapout(struct proc *p);
 
 /*
  * MPSAFE
+ *
+ * WARNING!  This code calls vm_map_check_protection() which only checks
+ * the associated vm_map_entry range.  It does not determine whether the
+ * contents of the memory is actually readable or writable.  In most cases
+ * just checking the vm_map_entry is sufficient within the kernel's address
+ * space.
  */
 int
 kernacc(addr, len, rw)
@@ -142,6 +148,12 @@ kernacc(addr, len, rw)
 
 /*
  * MPSAFE
+ *
+ * WARNING!  This code calls vm_map_check_protection() which only checks
+ * the associated vm_map_entry range.  It does not determine whether the
+ * contents of the memory is actually readable or writable.  vmapbuf(),
+ * vm_fault_quick(), or copyin()/copout()/su*()/fu*() functions should be
+ * used in conjuction with this call.
  */
 int
 useracc(addr, len, rw)

sys/vm/vm_map.c

@@ -2179,9 +2179,14 @@ vm_map_remove(vm_map_t map, vm_offset_t start, vm_offset_t end)
 /*
  *	vm_map_check_protection:
  *
- *	Assert that the target map allows the specified
- *	privilege on the entire address region given.
- *	The entire region must be allocated.
+ *	Assert that the target map allows the specified privilege on the
+ *	entire address region given.  The entire region must be allocated.
+ *
+ *	WARNING!  This code does not and should not check whether the
+ *	contents of the region is accessible.  For example a smaller file
+ *	might be mapped into a larger address space.
+ *
+ *	NOTE!  This code is also called by munmap().
  */
 boolean_t
 vm_map_check_protection(vm_map_t map, vm_offset_t start, vm_offset_t end,