Re: [kbuild] [linux-next:master 6931/12022] drivers/vfio/vfio_iommu_type1.c:1093 vfio_dma_do_unmap() warn: impossible condition '(size > (~0)) => (0-u32max > u32max)'

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 22 Feb 2021 15:51:45 -0700
Alex Williamson <alex.williamson@redhat.com> wrote:

> On Mon, 22 Feb 2021 17:10:43 +0300
> Dan Carpenter <dan.carpenter@oracle.com> wrote:
> 
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git  master
> > head:   37dfbfbdca66834bc0f64ec9b35e09ac6c8898da
> > commit: 0f53afa12baec8c00f5d1d6afb49325ada105253 [6931/12022] vfio/type1: unmap cleanup  
> 
> It's always the patches that claim no functional change... ;)
> 
> > config: i386-randconfig-m021-20210222 (attached as .config)
> > compiler: gcc-9 (Debian 9.3.0-15) 9.3.0
> > 
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp@intel.com>
> > Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> > 
> > New smatch warnings:
> > drivers/vfio/vfio_iommu_type1.c:1093 vfio_dma_do_unmap() warn: impossible condition '(size > (~0)) => (0-u32max > u32max)'
> > 
> > vim +1093 drivers/vfio/vfio_iommu_type1.c
> > 
> > 73fa0d10d077d9 Alex Williamson 2012-07-31  1071  static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
> > 331e33d2960c82 Kirti Wankhede  2020-05-29  1072  			     struct vfio_iommu_type1_dma_unmap *unmap,
> > 331e33d2960c82 Kirti Wankhede  2020-05-29  1073  			     struct vfio_bitmap *bitmap)
> > 73fa0d10d077d9 Alex Williamson 2012-07-31  1074  {
> > c086de818dd81c Kirti Wankhede  2016-11-17  1075  	struct vfio_dma *dma, *dma_last = NULL;
> > 331e33d2960c82 Kirti Wankhede  2020-05-29  1076  	size_t unmapped = 0, pgsize;
> > 0f53afa12baec8 Steve Sistare   2021-01-29  1077  	int ret = -EINVAL, retries = 0;
> > 331e33d2960c82 Kirti Wankhede  2020-05-29  1078  	unsigned long pgshift;
> > 0f53afa12baec8 Steve Sistare   2021-01-29  1079  	dma_addr_t iova = unmap->iova;
> > 0f53afa12baec8 Steve Sistare   2021-01-29  1080  	unsigned long size = unmap->size;
> >                                                         ^^^^^^^^^^^^^^^^^^
> > 
> > 73fa0d10d077d9 Alex Williamson 2012-07-31  1081  
> > cade075f265b25 Kirti Wankhede  2020-05-29  1082  	mutex_lock(&iommu->lock);
> > cade075f265b25 Kirti Wankhede  2020-05-29  1083  
> > 331e33d2960c82 Kirti Wankhede  2020-05-29  1084  	pgshift = __ffs(iommu->pgsize_bitmap);
> > 331e33d2960c82 Kirti Wankhede  2020-05-29  1085  	pgsize = (size_t)1 << pgshift;
> > cade075f265b25 Kirti Wankhede  2020-05-29  1086  
> > 0f53afa12baec8 Steve Sistare   2021-01-29  1087  	if (iova & (pgsize - 1))
> > cade075f265b25 Kirti Wankhede  2020-05-29  1088  		goto unlock;
> > cade075f265b25 Kirti Wankhede  2020-05-29  1089  
> > 0f53afa12baec8 Steve Sistare   2021-01-29  1090  	if (!size || size & (pgsize - 1))
> > cade075f265b25 Kirti Wankhede  2020-05-29  1091  		goto unlock;
> > 73fa0d10d077d9 Alex Williamson 2012-07-31  1092  
> > 0f53afa12baec8 Steve Sistare   2021-01-29 @1093  	if (iova + size - 1 < iova || size > SIZE_MAX)
> > 
> > size is unsigned long and SIZE_MAX is ULONG_MAX so "size > SIZE_MAX"
> > does not make sense.  
> 
> I think it made sense before the above commit, where unmap->size is a
> __u64 and a user could provide a value that exceeds SIZE_MAX on ILP32.
> Seems like the fix is probably to use a size_t for the local variable
> and restore this test to compare (unmap->size > SIZE_MAX).  Steve?

Actually it seems like VFIO_DMA_UNMAP_FLAG_ALL doesn't work when
PHYS_ADDR_MAX != SIZE_MAX (ex. x86 PAE - I think).  I can't say I'm
really interested in adding complexity to make it work in such a case
either.  Maybe we can just not expose it, ex:

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index ed03f3fcb07e..6b69a74b3db0 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -1207,7 +1207,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
 	int ret = -EINVAL, retries = 0;
 	unsigned long pgshift;
 	dma_addr_t iova = unmap->iova;
-	unsigned long size = unmap->size;
+	size_t size = unmap->size;
 	bool unmap_all = unmap->flags & VFIO_DMA_UNMAP_FLAG_ALL;
 	bool invalidate_vaddr = unmap->flags & VFIO_DMA_UNMAP_FLAG_VADDR;
 	struct rb_node *n, *first_n;
@@ -1228,7 +1228,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
 		goto unlock;
 	}
 
-	if (iova + size - 1 < iova || size > SIZE_MAX)
+	if (iova + size - 1 < iova || unmap->size > SIZE_MAX)
 		goto unlock;
 
 	/* When dirty tracking is enabled, allow only min supported pgsize */
@@ -2657,9 +2657,10 @@ static int vfio_iommu_type1_check_extension(struct vfio_iommu *iommu,
 	case VFIO_TYPE1_IOMMU:
 	case VFIO_TYPE1v2_IOMMU:
 	case VFIO_TYPE1_NESTING_IOMMU:
-	case VFIO_UNMAP_ALL:
 	case VFIO_UPDATE_VADDR:
 		return 1;
+	case VFIO_UNMAP_ALL:
+		return PHYS_ADDR_MAX == SIZE_MAX ? 1 : 0;
 	case VFIO_DMA_CC_IOMMU:
 		if (!iommu)
 			return 0;
@@ -2868,6 +2869,10 @@ static int vfio_iommu_type1_unmap_dma(struct vfio_iommu *iommu,
 			    VFIO_DMA_UNMAP_FLAG_VADDR)))
 		return -EINVAL;
 
+	if ((PHYS_ADDR_MAX != SIZE_MAX) &&
+	    (unmap.flags & VFIO_DMA_UNMAP_FLAG_ALL))
+		return -EINVAL;
+
 	if (unmap.flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) {
 		unsigned long pgshift;
 

 


> > Is the " - 1" intentional on the other overflow check?  As in it's okay
> > to wrap around to zero but not further than that?  Sometimes this is
> > intentional but it requires more subsystem expertise than I possess.  
> 
> Yes, since we're dealing with a start + length we need to account for
> the -1 in the end value, otherwise the user could never unmap the last
> page of the address space.  Thanks for the report!
> 
> Alex
> 
> > cade075f265b25 Kirti Wankhede  2020-05-29  1094  		goto unlock;
> > 73fa0d10d077d9 Alex Williamson 2012-07-31  1095  
> > 331e33d2960c82 Kirti Wankhede  2020-05-29  1096  	/* When dirty tracking is enabled, allow only min supported pgsize */
> > 331e33d2960c82 Kirti Wankhede  2020-05-29  1097  	if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
> > 331e33d2960c82 Kirti Wankhede  2020-05-29  1098  	    (!iommu->dirty_page_tracking || (bitmap->pgsize != pgsize))) {
> > 331e33d2960c82 Kirti Wankhede  2020-05-29  1099  		goto unlock;
> > 331e33d2960c82 Kirti Wankhede  2020-05-29  1100  	}
> > 73fa0d10d077d9 Alex Williamson 2012-07-31  1101  
> > 331e33d2960c82 Kirti Wankhede  2020-05-29  1102  	WARN_ON((pgsize - 1) & PAGE_MASK);
> > 331e33d2960c82 Kirti Wankhede  2020-05-29  1103  again:
> > 1ef3e2bc04223f Alex Williamson 2014-02-26  1104  	/*
> > 
> > ---
> > 0-DAY CI Kernel Test Service, Intel Corporation
> > https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org   
>