[PATCH v7 4/7] swiotlb: Zero out bounce buffer for untrusted device

From: Lu Baolu <baolu.lu@linux.intel.com>
To: David Woodhouse <dwmw2@infradead.org>,
	Joerg Roedel <joro@8bytes.org>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Christoph Hellwig <hch@lst.de>
Cc: ashok.raj@intel.com, jacob.jun.pan@intel.com, alan.cox@intel.com,
	kevin.tian@intel.com, mika.westerberg@linux.intel.com,
	Ingo Molnar <mingo@redhat.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	pengfei.xu@intel.com,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Juergen Gross <jgross@suse.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
	Lu Baolu <baolu.lu@linux.intel.com>
Subject: [PATCH v7 4/7] swiotlb: Zero out bounce buffer for untrusted device
Date: Fri, 23 Aug 2019 15:17:32 +0800	[thread overview]
Message-ID: <20190823071735.30264-5-baolu.lu@linux.intel.com> (raw)
In-Reply-To: <20190823071735.30264-1-baolu.lu@linux.intel.com>

This is necessary to avoid exposing valid kernel data to any
malicious device.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 kernel/dma/swiotlb.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 89066efa3840..04bea5a87462 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -35,6 +35,7 @@
 #include <linux/scatterlist.h>
 #include <linux/mem_encrypt.h>
 #include <linux/set_memory.h>
+#include <linux/pci.h>
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
 #endif
@@ -458,6 +459,8 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
 	unsigned long offset_slots;
 	unsigned long max_slots;
 	unsigned long tmp_io_tlb_used;
+	void *zero_addr;
+	size_t zero_size;
 
 	if (no_iotlb_memory)
 		panic("Can not allocate SWIOTLB buffer earlier and can't now provide you with the DMA bounce buffer");
@@ -565,9 +568,20 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
 	 */
 	for (i = 0; i < nslots; i++)
 		io_tlb_orig_addr[index+i] = orig_addr + (i << IO_TLB_SHIFT);
+
+	zero_addr = phys_to_virt(tlb_addr);
+	zero_size = alloc_size;
+
 	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
-	    (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL))
+	    (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)) {
 		swiotlb_bounce(orig_addr, tlb_addr, mapping_size, DMA_TO_DEVICE);
+		zero_addr += mapping_size;
+		zero_size -= mapping_size;
+	}
+
+	/* Zero out the bounce buffer if the consumer is untrusted. */
+	if (dev_is_untrusted(hwdev) && zero_size)
+		memset(zero_addr, 0, zero_size);
 
 	return tlb_addr;
 }
-- 
2.17.1

