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authorDaniel Vetter <daniel.vetter@ffwll.ch>2021-01-15 17:47:39 +0100
committerDaniel Vetter <daniel.vetter@ffwll.ch>2021-01-18 14:26:51 +0100
commit84335675f2223cbd25d0de7d38ecc7d40b95bd4a (patch)
tree7d2ac804ca7643debcdc6eeb11a02c5ebfca0059 /drivers/dma-buf
parent72fec10c17d95bcb99371f5b29f6947e67d7493b (diff)
dma-buf: Add debug option
We have too many people abusing the struct page they can get at but really shouldn't in importers. Aside from that the backing page might simply not exist (for dynamic p2p mappings) looking at it and using it e.g. for mmap can also wreak the page handling of the exporter completely. Importers really must go through the proper interface like dma_buf_mmap for everything. I'm semi-tempted to enforce this for dynamic importers since those really have no excuse at all to break the rules. Unfortuantely we can't store the right pointers somewhere safe to make sure we oops on something recognizable, so best is to just wrangle them a bit by flipping all the bits. At least on x86 kernel addresses have all their high bits sets and the struct page array is fairly low in the kernel mapping, so flipping all the bits gives us a very high pointer in userspace and hence excellent chances for an invalid dereference. v2: Add a note to the @map_dma_buf hook that exporters shouldn't do fancy caching tricks, which would blow up with this address scrambling trick here (Chris) Enable by default when CONFIG_DMA_API_DEBUG is enabled. v3: Only one copy of the mangle/unmangle code (Christian) v4: #ifdef, not #if (0day) v5: sg_table can also be an ERR_PTR (Chris, Christian) Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Christian König <christian.koenig@amd.com> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> Cc: Chris Wilson <chris@chris-wilson.co.uk> Cc: Sumit Semwal <sumit.semwal@linaro.org> Cc: "Christian König" <christian.koenig@amd.com> Cc: David Stevens <stevensd@chromium.org> Cc: linux-media@vger.kernel.org Cc: linaro-mm-sig@lists.linaro.org Link: https://patchwork.freedesktop.org/patch/msgid/20210115164739.3958206-1-daniel.vetter@ffwll.ch
Diffstat (limited to 'drivers/dma-buf')
-rw-r--r--drivers/dma-buf/Kconfig8
-rw-r--r--drivers/dma-buf/dma-buf.c46
2 files changed, 50 insertions, 4 deletions
diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
index 4f8224a6ac95..4e16c71c24b7 100644
--- a/drivers/dma-buf/Kconfig
+++ b/drivers/dma-buf/Kconfig
@@ -50,6 +50,14 @@ config DMABUF_MOVE_NOTIFY
This is marked experimental because we don't yet have a consistent
execution context and memory management between drivers.
+config DMABUF_DEBUG
+ bool "DMA-BUF debug checks"
+ default y if DMA_API_DEBUG
+ help
+ This option enables additional checks for DMA-BUF importers and
+ exporters. Specifically it validates that importers do not peek at the
+ underlying struct page when they import a buffer.
+
config DMABUF_SELFTESTS
tristate "Selftests for the dma-buf interfaces"
default n
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index b8465243eca2..3948b88aa123 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -653,6 +653,34 @@ void dma_buf_put(struct dma_buf *dmabuf)
}
EXPORT_SYMBOL_GPL(dma_buf_put);
+static void mangle_sg_table(struct sg_table *sg_table)
+{
+#ifdef CONFIG_DMABUF_DEBUG
+ int i;
+ struct scatterlist *sg;
+
+ /* To catch abuse of the underlying struct page by importers mix
+ * up the bits, but take care to preserve the low SG_ bits to
+ * not corrupt the sgt. The mixing is undone in __unmap_dma_buf
+ * before passing the sgt back to the exporter. */
+ for_each_sgtable_sg(sg_table, sg, i)
+ sg->page_link ^= ~0xffUL;
+#endif
+
+}
+static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
+ enum dma_data_direction direction)
+{
+ struct sg_table *sg_table;
+
+ sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
+
+ if (!IS_ERR_OR_NULL(sg_table))
+ mangle_sg_table(sg_table);
+
+ return sg_table;
+}
+
/**
* dma_buf_dynamic_attach - Add the device to dma_buf's attachments list
* @dmabuf: [in] buffer to attach device to.
@@ -724,7 +752,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
goto err_unlock;
}
- sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
+ sgt = __map_dma_buf(attach, DMA_BIDIRECTIONAL);
if (!sgt)
sgt = ERR_PTR(-ENOMEM);
if (IS_ERR(sgt)) {
@@ -771,6 +799,16 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
}
EXPORT_SYMBOL_GPL(dma_buf_attach);
+static void __unmap_dma_buf(struct dma_buf_attachment *attach,
+ struct sg_table *sg_table,
+ enum dma_data_direction direction)
+{
+ /* uses XOR, hence this unmangles */
+ mangle_sg_table(sg_table);
+
+ attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
+}
+
/**
* dma_buf_detach - Remove the given attachment from dmabuf's attachments list
* @dmabuf: [in] buffer to detach from.
@@ -789,7 +827,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
if (dma_buf_is_dynamic(attach->dmabuf))
dma_resv_lock(attach->dmabuf->resv, NULL);
- dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
+ __unmap_dma_buf(attach, attach->sgt, attach->dir);
if (dma_buf_is_dynamic(attach->dmabuf)) {
dma_buf_unpin(attach);
@@ -911,7 +949,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
}
}
- sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
+ sg_table = __map_dma_buf(attach, direction);
if (!sg_table)
sg_table = ERR_PTR(-ENOMEM);
@@ -974,7 +1012,7 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
if (dma_buf_is_dynamic(attach->dmabuf))
dma_resv_assert_held(attach->dmabuf->resv);
- attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
+ __unmap_dma_buf(attach, sg_table, direction);
if (dma_buf_is_dynamic(attach->dmabuf) &&
!IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))