swiotlb: add overflow checks to swiotlb_bounce

This is a follow-up on 5f89468e ("swiotlb: manipulate orig_addr
when tlb_addr has offset") which fixed unaligned dma mappings,
making sure the following overflows are caught:

- offset of the start of the slot within the device bigger than
requested address' offset, in other words if the base address
given in swiotlb_tbl_map_single to create the mapping (orig_addr)
was after the requested address for the sync (tlb_offset) in the
same block:

 |------------------------------------------| block
              <----------------------------> mapped part of the block
              ^
              orig_addr
       ^
       invalid tlb_addr for sync

- if the resulting offset was bigger than the allocation size
this one could happen if the mapping was not until the end. e.g.

 |------------------------------------------| block
      <---------------------> mapped part of the block
      ^                               ^
      orig_addr                       invalid tlb_addr

Both should never happen so print a warning and bail out without trying
to adjust the sizes/offsets: the first one could try to sync from
orig_addr to whatever is left of the requested size, but the later
really has nothing to sync there...
Signed-off-by: Dominique Martinet <dominique.martinet@atmark-techno.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Bumyong Lee <bumyong.lee@samsung.com
Cc: Chanho Park <chanho61.park@samsung.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Konrad Rzeszutek Wilk <konrad@kernel.org>

kernel/dma/swiotlb.c

@@ -365,13 +365,27 @@ static void swiotlb_bounce(struct device *dev, phys_addr_t tlb_addr, size_t size
 	size_t alloc_size = mem->slots[index].alloc_size;
 	unsigned long pfn = PFN_DOWN(orig_addr);
 	unsigned char *vaddr = phys_to_virt(tlb_addr);
-	unsigned int tlb_offset;
+	unsigned int tlb_offset, orig_addr_offset;
 
 	if (orig_addr == INVALID_PHYS_ADDR)
 		return;
 
-	tlb_offset = (tlb_addr & (IO_TLB_SIZE - 1)) -
-		     swiotlb_align_offset(dev, orig_addr);
+	tlb_offset = tlb_addr & (IO_TLB_SIZE - 1);
+	orig_addr_offset = swiotlb_align_offset(dev, orig_addr);
+	if (tlb_offset < orig_addr_offset) {
+		dev_WARN_ONCE(dev, 1,
+			"Access before mapping start detected. orig offset %u, requested offset %u.\n",
+			orig_addr_offset, tlb_offset);
+		return;
+	}
+
+	tlb_offset -= orig_addr_offset;
+	if (tlb_offset > alloc_size) {
+		dev_WARN_ONCE(dev, 1,
+			"Buffer overflow detected. Allocation size: %zu. Mapping size: %zu+%u.\n",
+			alloc_size, size, tlb_offset);
+		return;
+	}
 
 	orig_addr += tlb_offset;
 	alloc_size -= tlb_offset;