From cf27ec930be906e142c752f9161197d69ca534d7 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 11 Aug 2015 16:48:32 +0100 Subject: [PATCH] iommu/io-pgtable-arm: Unmap and free table when overwriting with block When installing a block mapping, we unconditionally overwrite a non-leaf PTE if we find one. However, this can cause a problem if the following sequence of events occur: (1) iommu_map called for a 4k (i.e. PAGE_SIZE) mapping at some address - We initialise the page table all the way down to a leaf entry - No TLB maintenance is required, because we're going from invalid to valid. (2) iommu_unmap is called on the mapping installed in (1) - We walk the page table to the final (leaf) entry and zero it - We only changed a valid leaf entry, so we invalidate leaf-only (3) iommu_map is called on the same address as (1), but this time for a 2MB (i.e. BLOCK_SIZE) mapping) - We walk the page table down to the penultimate level, where we find a table entry - We overwrite the table entry with a block mapping and return without any TLB maintenance and without freeing the memory used by the now-orphaned table. This last step can lead to a walk-cache caching the overwritten table entry, causing unexpected faults when the new mapping is accessed by a device. One way to fix this would be to collapse the page table when freeing the last page at a given level, but this would require expensive iteration on every map call. Instead, this patch detects the case when we are overwriting a table entry and explicitly unmaps the table first, which takes care of both freeing and TLB invalidation. Cc: Reported-by: Brian Starkey Tested-by: Brian Starkey Signed-off-by: Will Deacon Signed-off-by: Joerg Roedel --- drivers/iommu/io-pgtable-arm.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c index e4bc2b23ab96..73c07482f487 100644 --- a/drivers/iommu/io-pgtable-arm.c +++ b/drivers/iommu/io-pgtable-arm.c @@ -263,6 +263,10 @@ static void __arm_lpae_set_pte(arm_lpae_iopte *ptep, arm_lpae_iopte pte, sizeof(pte), DMA_TO_DEVICE); } +static int __arm_lpae_unmap(struct arm_lpae_io_pgtable *data, + unsigned long iova, size_t size, int lvl, + arm_lpae_iopte *ptep); + static int arm_lpae_init_pte(struct arm_lpae_io_pgtable *data, unsigned long iova, phys_addr_t paddr, arm_lpae_iopte prot, int lvl, @@ -271,10 +275,21 @@ static int arm_lpae_init_pte(struct arm_lpae_io_pgtable *data, arm_lpae_iopte pte = prot; struct io_pgtable_cfg *cfg = &data->iop.cfg; - /* We require an unmap first */ if (iopte_leaf(*ptep, lvl)) { + /* We require an unmap first */ WARN_ON(!selftest_running); return -EEXIST; + } else if (iopte_type(*ptep, lvl) == ARM_LPAE_PTE_TYPE_TABLE) { + /* + * We need to unmap and free the old table before + * overwriting it with a block entry. + */ + arm_lpae_iopte *tblp; + size_t sz = ARM_LPAE_BLOCK_SIZE(lvl, data); + + tblp = ptep - ARM_LPAE_LVL_IDX(iova, lvl, data); + if (WARN_ON(__arm_lpae_unmap(data, iova, sz, lvl, tblp) != sz)) + return -EINVAL; } if (cfg->quirks & IO_PGTABLE_QUIRK_ARM_NS) -- 2.11.0