The size of the buffer being bounced is not checked if it happens to be larger than the size of the mapped buffer. Because the size can be controlled by a device, as it's the case with virtio devices, this can lead to memory corruption.
This patch saves the remaining buffer memory for each slab and uses that information for validation in the sync/unmap paths before swiotlb_bounce is called. Validating this argument is important under the threat models of AMD SEV-SNP and Intel TDX, where the HV is considered untrusted. Signed-off-by: Martin Radev <[email protected]> --- kernel/dma/swiotlb.c | 52 ++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 50 insertions(+), 2 deletions(-) diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 7c42df6e6100..98d79103aa1f 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -102,6 +102,11 @@ static unsigned int max_segment; #define INVALID_PHYS_ADDR (~(phys_addr_t)0) static phys_addr_t *io_tlb_orig_addr; +/* + * The mapped buffer's size should be validated during a sync operation. + */ +static size_t *io_tlb_orig_size; + /* * Protect the above data structures in the map and unmap calls */ @@ -240,9 +245,16 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose) panic("%s: Failed to allocate %zu bytes align=0x%lx\n", __func__, alloc_size, PAGE_SIZE); + alloc_size = PAGE_ALIGN(io_tlb_nslabs * sizeof(size_t)); + io_tlb_orig_size = memblock_alloc(alloc_size, PAGE_SIZE); + if (!io_tlb_orig_size) + panic("%s: Failed to allocate %zu bytes align=0x%lx\n", + __func__, alloc_size, PAGE_SIZE); + for (i = 0; i < io_tlb_nslabs; i++) { io_tlb_list[i] = IO_TLB_SEGSIZE - OFFSET(i, IO_TLB_SEGSIZE); io_tlb_orig_addr[i] = INVALID_PHYS_ADDR; + io_tlb_orig_size[i] = 0; } io_tlb_index = 0; no_iotlb_memory = false; @@ -363,7 +375,7 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs) * between io_tlb_start and io_tlb_end. */ io_tlb_list = (unsigned int *)__get_free_pages(GFP_KERNEL, - get_order(io_tlb_nslabs * sizeof(int))); + get_order(io_tlb_nslabs * sizeof(int))); if (!io_tlb_list) goto cleanup3; @@ -374,9 +386,18 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs) if (!io_tlb_orig_addr) goto cleanup4; + io_tlb_orig_size = (size_t *) + __get_free_pages(GFP_KERNEL, + get_order(io_tlb_nslabs * + sizeof(size_t))); + if (!io_tlb_orig_size) + goto cleanup5; + + for (i = 0; i < io_tlb_nslabs; i++) { io_tlb_list[i] = IO_TLB_SEGSIZE - OFFSET(i, IO_TLB_SEGSIZE); io_tlb_orig_addr[i] = INVALID_PHYS_ADDR; + io_tlb_orig_size[i] = 0; } io_tlb_index = 0; no_iotlb_memory = false; @@ -389,6 +410,10 @@ swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs) return 0; +cleanup5: + free_pages((unsigned long)io_tlb_orig_addr, get_order(io_tlb_nslabs * + sizeof(phys_addr_t))); + cleanup4: free_pages((unsigned long)io_tlb_list, get_order(io_tlb_nslabs * sizeof(int))); @@ -404,6 +429,8 @@ void __init swiotlb_exit(void) return; if (late_alloc) { + free_pages((unsigned long)io_tlb_orig_size, + get_order(io_tlb_nslabs * sizeof(size_t))); free_pages((unsigned long)io_tlb_orig_addr, get_order(io_tlb_nslabs * sizeof(phys_addr_t))); free_pages((unsigned long)io_tlb_list, get_order(io_tlb_nslabs * @@ -413,6 +440,8 @@ void __init swiotlb_exit(void) } else { memblock_free_late(__pa(io_tlb_orig_addr), PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t))); + memblock_free_late(__pa(io_tlb_orig_size), + PAGE_ALIGN(io_tlb_nslabs * sizeof(size_t))); memblock_free_late(__pa(io_tlb_list), PAGE_ALIGN(io_tlb_nslabs * sizeof(int))); memblock_free_late(io_tlb_start, @@ -581,8 +610,10 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, phys_addr_t orig_addr, * This is needed when we sync the memory. Then we sync the buffer if * needed. */ - for (i = 0; i < nslots; i++) + for (i = 0; i < nslots; i++) { io_tlb_orig_addr[index+i] = orig_addr + (i << IO_TLB_SHIFT); + io_tlb_orig_size[index+i] = alloc_size - (i << IO_TLB_SHIFT); + } if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) && (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)) swiotlb_bounce(orig_addr, tlb_addr, mapping_size, DMA_TO_DEVICE); @@ -590,6 +621,17 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, phys_addr_t orig_addr, return tlb_addr; } +static void validate_sync_size_and_truncate(struct device *hwdev, size_t orig_size, size_t *size) +{ + if (*size > orig_size) { + /* Warn and truncate mapping_size */ + dev_WARN_ONCE(hwdev, 1, + "Attempt for buffer overflow. Original size: %zu. Mapping size: %zu.\n", + orig_size, *size); + *size = orig_size; + } +} + /* * tlb_addr is the physical address of the bounce buffer to unmap. */ @@ -602,6 +644,8 @@ void swiotlb_tbl_unmap_single(struct device *hwdev, phys_addr_t tlb_addr, int index = (tlb_addr - io_tlb_start) >> IO_TLB_SHIFT; phys_addr_t orig_addr = io_tlb_orig_addr[index]; + validate_sync_size_and_truncate(hwdev, io_tlb_orig_size[index], &mapping_size); + /* * First, sync the memory before unmapping the entry */ @@ -627,6 +671,7 @@ void swiotlb_tbl_unmap_single(struct device *hwdev, phys_addr_t tlb_addr, for (i = index + nslots - 1; i >= index; i--) { io_tlb_list[i] = ++count; io_tlb_orig_addr[i] = INVALID_PHYS_ADDR; + io_tlb_orig_size[i] = 0; } /* * Step 2: merge the returned slots with the preceding slots, @@ -645,12 +690,15 @@ void swiotlb_tbl_sync_single(struct device *hwdev, phys_addr_t tlb_addr, enum dma_sync_target target) { int index = (tlb_addr - io_tlb_start) >> IO_TLB_SHIFT; + size_t orig_size = io_tlb_orig_size[index]; phys_addr_t orig_addr = io_tlb_orig_addr[index]; if (orig_addr == INVALID_PHYS_ADDR) return; orig_addr += (unsigned long)tlb_addr & ((1 << IO_TLB_SHIFT) - 1); + validate_sync_size_and_truncate(hwdev, orig_size, &size); + switch (target) { case SYNC_FOR_CPU: if (likely(dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL)) -- 2.17.1
