linux-kernel - [PATCH AUTOSEL 4.18 05/88] iommu/io-pgtable-arm-v7s: Abort allocation when table address overflows the PTE

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Message-ID: <20180907003547.57567-5-alexander.levin@microsoft.com>
Date:   Fri, 7 Sep 2018 00:35:56 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        Will Deacon <will.deacon@....com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL 4.18 05/88] iommu/io-pgtable-arm-v7s: Abort allocation
 when table address overflows the PTE

From: Jean-Philippe Brucker <jean-philippe.brucker@....com>

[ Upstream commit 29859aeb8a6ea17ba207933a81b6b77b4d4df81a ]

When run on a 64-bit system in selftest, the v7s driver may obtain page
table with physical addresses larger than 32-bit. Level-2 tables are 1KB
and are are allocated with slab, which doesn't accept the GFP_DMA32
flag. Currently map() truncates the address written in the PTE, causing
iova_to_phys() or unmap() to access invalid memory. Kasan reports it as
a use-after-free. To avoid any nasty surprise, test if the physical
address fits in a PTE before returning a new table. 32-bit systems,
which are the main users of this page table format, shouldn't see any
difference.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@....com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 drivers/iommu/io-pgtable-arm-v7s.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/io-pgtable-arm-v7s.c b/drivers/iommu/io-pgtable-arm-v7s.c
index 50e3a9fcf43e..b5948ba6b3b3 100644
--- a/drivers/iommu/io-pgtable-arm-v7s.c
+++ b/drivers/iommu/io-pgtable-arm-v7s.c
@@ -192,6 +192,7 @@ static void *__arm_v7s_alloc_table(int lvl, gfp_t gfp,
 {
 	struct io_pgtable_cfg *cfg = &data->iop.cfg;
 	struct device *dev = cfg->iommu_dev;
+	phys_addr_t phys;
 	dma_addr_t dma;
 	size_t size = ARM_V7S_TABLE_SIZE(lvl);
 	void *table = NULL;
@@ -200,6 +201,10 @@ static void *__arm_v7s_alloc_table(int lvl, gfp_t gfp,
 		table = (void *)__get_dma_pages(__GFP_ZERO, get_order(size));
 	else if (lvl == 2)
 		table = kmem_cache_zalloc(data->l2_tables, gfp | GFP_DMA);
+	phys = virt_to_phys(table);
+	if (phys != (arm_v7s_iopte)phys)
+		/* Doesn't fit in PTE */
+		goto out_free;
 	if (table && !(cfg->quirks & IO_PGTABLE_QUIRK_NO_DMA)) {
 		dma = dma_map_single(dev, table, size, DMA_TO_DEVICE);
 		if (dma_mapping_error(dev, dma))
@@ -209,7 +214,7 @@ static void *__arm_v7s_alloc_table(int lvl, gfp_t gfp,
 		 * address directly, so if the DMA layer suggests otherwise by
 		 * translating or truncating them, that bodes very badly...
 		 */
-		if (dma != virt_to_phys(table))
+		if (dma != phys)
 			goto out_unmap;
 	}
 	kmemleak_ignore(table);
-- 
2.17.1