On 2025/7/18 03:15, Jason Gunthorpe wrote:

When allocating IOVA the candidate range gets aligned to the target alignment. If the range is close to ULONG_MAX then the ALIGN() can wrap resulting in a corrupted iova.

Open code the ALIGN() using get_add_overflow() to prevent this. This simplifies the checks as we don't need to check for length earlier either.

Consolidate the two copies of this code under a single helper.

This bug would allow userspace to create a mapping that overlaps with some other mapping or a reserved range.

Cc: stable@vger.kernel.org Fixes: 51fe6141f0f6 ("iommufd: Data structure to provide IOVA to PFN mapping") Reported-by: syzbot+c2f65e2801743ca64e08@syzkaller.appspotmail.com Closes: https://lore.kernel.org/r/685af644.a00a0220.2e5631.0094.GAE@google.com Signed-off-by: Jason Gunthorpe jgg@nvidia.com

---

drivers/iommu/iommufd/io_pagetable.c | 41 +++++++++++++++++----------- 1 file changed, 25 insertions(+), 16 deletions(-)

Reviewed-by: Yi Liu yi.l.liu@intel.com

diff --git a/drivers/iommu/iommufd/io_pagetable.c b/drivers/iommu/iommufd/io_pagetable.c index abf4aadca96c0b..c0360c450880b8 100644 --- a/drivers/iommu/iommufd/io_pagetable.c +++ b/drivers/iommu/iommufd/io_pagetable.c @@ -70,20 +70,34 @@ struct iopt_area *iopt_area_contig_next(struct iopt_area_contig_iter *iter) return iter->area; } +static bool __alloc_iova_check_range(unsigned long *start, unsigned long last,

• 		     unsigned long length,
  

• 		     unsigned long iova_alignment,
  

• 		     unsigned long page_offset)
  

+{

• unsigned long aligned_start;
• /* ALIGN_UP() */
• if (check_add_overflow(*start, iova_alignment - 1, &aligned_start))

• return false;
  

• aligned_start &= ~(iova_alignment - 1);
• aligned_start |= page_offset;
• if (aligned_start >= last || last - aligned_start < length - 1)

• return false;
  

• *start = aligned_start;
• return true;

+}

• static bool __alloc_iova_check_hole(struct interval_tree_double_span_iter *span, unsigned long length, unsigned long iova_alignment, unsigned long page_offset) {

• if (span->is_used || span->last_hole - span->start_hole < length - 1)

• if (span->is_used) return false;

• span->start_hole = ALIGN(span->start_hole, iova_alignment) |

• 	   page_offset;
  

• if (span->start_hole > span->last_hole ||

•    span->last_hole - span->start_hole < length - 1)
  

• return false;
  

• return true;

• return __alloc_iova_check_range(&span->start_hole, span->last_hole,

• 			length, iova_alignment, page_offset);
  

  }

static bool __alloc_iova_check_used(struct interval_tree_span_iter *span, @@ -91,15 +105,10 @@ static bool __alloc_iova_check_used(struct interval_tree_span_iter *span, unsigned long iova_alignment, unsigned long page_offset) {

• if (span->is_hole || span->last_used - span->start_used < length - 1)

• if (span->is_hole) return false;

• span->start_used = ALIGN(span->start_used, iova_alignment) |

• 	   page_offset;
  

• if (span->start_used > span->last_used ||

•    span->last_used - span->start_used < length - 1)
  

• return false;
  

• return true;

• return __alloc_iova_check_range(&span->start_used, span->last_used,

• 			length, iova_alignment, page_offset);
  

  }

/*

On Fri, Jul 18, 2025 at 11:50:30AM -0700, Nicolin Chen wrote:

0xfffffffffff80001 and 0x50000 could repro with 64K pages, exactly what your math works :)

Okay, I was also worried we'd get into trouble with how iova_alignment might be working but if it's fine lets do this then:

@@ -975,18 +975,24 @@ TEST_F(iommufd_ioas, reserved_overflow) .size = sizeof(test_cmd), .op = IOMMU_TEST_OP_ADD_RESERVED, .id = self->ioas_id, - .add_reserved = { .start = 6, - .length = 0xffffffffffff8001 }, + .add_reserved.start = 6, }; + unsigned int map_len; __u64 iova;

- if (PAGE_SIZE != 4096) - SKIP(return, "Test requires 4k PAGE_SIZE"); + if (PAGE_SIZE == 4096) { + test_cmd.add_reserved.length = 0xffffffffffff8001; + map_len = 0x5000; + } else { + test_cmd.add_reserved.length = + 0xffffffffffffffff - MOCK_PAGE_SIZE * 16; + map_len = MOCK_PAGE_SIZE * 10; + }

ASSERT_EQ(0, ioctl(self->fd, _IOMMU_TEST_CMD(IOMMU_TEST_OP_ADD_RESERVED), &test_cmd)); - test_err_ioctl_ioas_map(ENOSPC, buffer, 0x5000, &iova); + test_err_ioctl_ioas_map(ENOSPC, buffer, map_len, &iova); }

TEST_F(iommufd_ioas, area_allowed)

Thanks, Jason

On 2025/7/18 03:15, Jason Gunthorpe wrote:

This has triggered an overflow inside the ioas iova auto allocation logic, test it directly. Use the same stimulus syzkaller found.

Signed-off-by: Jason Gunthorpe jgg@nvidia.com

tools/testing/selftests/iommu/iommufd.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)

run it on intel x86. this test case failed without patch 01, and passed with patch 01.

Tested-by: Yi Liu yi.l.liu@intel.com

diff --git a/tools/testing/selftests/iommu/iommufd.c b/tools/testing/selftests/iommu/iommufd.c index d59d48022a24af..d9df92e27264b1 100644 --- a/tools/testing/selftests/iommu/iommufd.c +++ b/tools/testing/selftests/iommu/iommufd.c @@ -968,6 +968,24 @@ TEST_F(iommufd_ioas, area_auto_iova) test_ioctl_ioas_unmap(iovas[i], PAGE_SIZE * (i + 1)); } +/* https://lore.kernel.org/r/685af644.a00a0220.2e5631.0094.GAE@google.com */ +TEST_F(iommufd_ioas, reserved_overflow) +{

• struct iommu_test_cmd test_cmd = {

• .size = sizeof(test_cmd),
  

• .op = IOMMU_TEST_OP_ADD_RESERVED,
  

• .id = self->ioas_id,
  

• .add_reserved = { .start = 6,
  

• 		  .length = 0xffffffffffff8001 },
  

• };
• __u64 iova;
• ASSERT_EQ(0,

•   ioctl(self->fd, _IOMMU_TEST_CMD(IOMMU_TEST_OP_ADD_RESERVED),
  

• 	&test_cmd));
  

• test_err_ioctl_ioas_map(ENOSPC, buffer, 0x5000, &iova);

+}

• TEST_F(iommufd_ioas, area_allowed) { struct iommu_test_cmd test_cmd = {