iommufd/selftest: Fix buffer read overrrun in the dirty test

test_bit() is used to read the memory storing the bitmap, however
test_bit() always uses a unsigned long 8 byte access.

If the bitmap is not an aligned size of 64 bits this will now trigger a
KASAN warning reading past the end of the buffer.

Properly round the buffer allocation to an unsigned long size. Continue to
copy_from_user() using a byte granularity.

Fixes: 9560393b ("iommufd/selftest: Fix iommufd_test_dirty() to handle <u8 bitmaps")
Link: https://patch.msgid.link/r/0-v1-113e8d9e7861+5ae-iommufd_kasan_jgg@nvidia.comReviewed-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/iommu/iommufd/selftest.c

@@ -1343,7 +1343,7 @@ static int iommufd_test_dirty(struct iommufd_ucmd *ucmd, unsigned int mockpt_id,
 			      unsigned long page_size, void __user *uptr,
 			      u32 flags)
 {
-	unsigned long bitmap_size, i, max;
+	unsigned long i, max;
 	struct iommu_test_cmd *cmd = ucmd->cmd;
 	struct iommufd_hw_pagetable *hwpt;
 	struct mock_iommu_domain *mock;
@@ -1364,15 +1364,14 @@ static int iommufd_test_dirty(struct iommufd_ucmd *ucmd, unsigned int mockpt_id,
 	}
 
 	max = length / page_size;
-	bitmap_size = DIV_ROUND_UP(max, BITS_PER_BYTE);
-
-	tmp = kvzalloc(bitmap_size, GFP_KERNEL_ACCOUNT);
+	tmp = kvzalloc(DIV_ROUND_UP(max, BITS_PER_LONG) * sizeof(unsigned long),
+		       GFP_KERNEL_ACCOUNT);
 	if (!tmp) {
 		rc = -ENOMEM;
 		goto out_put;
 	}
 
-	if (copy_from_user(tmp, uptr, bitmap_size)) {
+	if (copy_from_user(tmp, uptr,DIV_ROUND_UP(max, BITS_PER_BYTE))) {
 		rc = -EFAULT;
 		goto out_free;
 	}