[PATCH 6.1 153/219] xen/gntdev: Fix the abuse of underlying struct page in DMA-buf import

Greg Kroah-Hartman
2024-02-03T04:10:45Z

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>

[ Upstream commit 2d2db7d40254d5fb53b11ebd703cd1ed0c5de7a1 ]

DO NOT access the underlying struct page of an sg table exported
by DMA-buf in dmabuf_imp_to_refs(), this is not allowed.
Please see drivers/dma-buf/dma-buf.c:mangle_sg_table() for details.

Fortunately, here (for special Xen device) we can avoid using
pages and calculate gfns directly from dma addresses provided by
the sg table.

Suggested-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Link: https://lore.kernel.org/r/20240107103426.2038075-1-olekstysh@gmail.com
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/xen/gntdev-dmabuf.c | 50 ++++++++++++++++++-------------------
1 file changed, 25 insertions(+), 25 deletions(-)

diff --git a/drivers/xen/gntdev-dmabuf.c b/drivers/xen/gntdev-dmabuf.c
index 940e5e9e8a54..335451309566 100644
--- a/drivers/xen/gntdev-dmabuf.c
+++ b/drivers/xen/gntdev-dmabuf.c
@@ -11,6 +11,7 @@
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/dma-buf.h>
+#include <linux/dma-direct.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/uaccess.h>
@@ -50,7 +51,7 @@ struct gntdev_dmabuf {

/* Number of pages this buffer has. */
int nr_pages;
- /* Pages of this buffer. */
+ /* Pages of this buffer (only for dma-buf export). */
struct page **pages;
};

@@ -484,7 +485,7 @@ static int dmabuf_exp_from_refs(struct gntdev_priv *priv, int flags,
/* DMA buffer import support. */

static int
-dmabuf_imp_grant_foreign_access(struct page **pages, u32 *refs,
+dmabuf_imp_grant_foreign_access(unsigned long *gfns, u32 *refs,
int count, int domid)
{
grant_ref_t priv_gref_head;
@@ -507,7 +508,7 @@ dmabuf_imp_grant_foreign_access(struct page **pages, u32 *refs,
}

gnttab_grant_foreign_access_ref(cur_ref, domid,
- xen_page_to_gfn(pages[i]), 0);
+ gfns[i], 0);
refs[i] = cur_ref;
}

@@ -529,7 +530,6 @@ static void dmabuf_imp_end_foreign_access(u32 *refs, int count)

static void dmabuf_imp_free_storage(struct gntdev_dmabuf *gntdev_dmabuf)
{
- kfree(gntdev_dmabuf->pages);
kfree(gntdev_dmabuf->u.imp.refs);
kfree(gntdev_dmabuf);
}
@@ -549,12 +549,6 @@ static struct gntdev_dmabuf *dmabuf_imp_alloc_storage(int count)
if (!gntdev_dmabuf->u.imp.refs)
goto fail;

- gntdev_dmabuf->pages = kcalloc(count,
- sizeof(gntdev_dmabuf->pages[0]),
- GFP_KERNEL);
- if (!gntdev_dmabuf->pages)
- goto fail;
-
gntdev_dmabuf->nr_pages = count;

for (i = 0; i < count; i++)
@@ -576,7 +570,8 @@ dmabuf_imp_to_refs(struct gntdev_dmabuf_priv *priv, struct device *dev,
struct dma_buf *dma_buf;
struct dma_buf_attachment *attach;
struct sg_table *sgt;
- struct sg_page_iter sg_iter;
+ struct sg_dma_page_iter sg_iter;
+ unsigned long *gfns;
int i;

dma_buf = dma_buf_get(fd);
@@ -624,26 +619,31 @@ dmabuf_imp_to_refs(struct gntdev_dmabuf_priv *priv, struct device *dev,

gntdev_dmabuf->u.imp.sgt = sgt;

- /* Now convert sgt to array of pages and check for page validity. */
+ gfns = kcalloc(count, sizeof(*gfns), GFP_KERNEL);
+ if (!gfns) {
+ ret = ERR_PTR(-ENOMEM);
+ goto fail_unmap;
+ }
+
+ /*
+ * Now convert sgt to array of gfns without accessing underlying pages.
+ * It is not allowed to access the underlying struct page of an sg table
+ * exported by DMA-buf, but since we deal with special Xen dma device here
+ * (not a normal physical one) look at the dma addresses in the sg table
+ * and then calculate gfns directly from them.
+ */
i = 0;
- for_each_sgtable_page(sgt, &sg_iter, 0) {
- struct page *page = sg_page_iter_page(&sg_iter);
- /*
- * Check if page is valid: this can happen if we are given
- * a page from VRAM or other resources which are not backed
- * by a struct page.
- */
- if (!pfn_valid(page_to_pfn(page))) {
- ret = ERR_PTR(-EINVAL);
- goto fail_unmap;
- }
+ for_each_sgtable_dma_page(sgt, &sg_iter, 0) {
+ dma_addr_t addr = sg_page_iter_dma_address(&sg_iter);
+ unsigned long pfn = bfn_to_pfn(XEN_PFN_DOWN(dma_to_phys(dev, addr)));

- gntdev_dmabuf->pages[i++] = page;
+ gfns[i++] = pfn_to_gfn(pfn);
}

- ret = ERR_PTR(dmabuf_imp_grant_foreign_access(gntdev_dmabuf->pages,
+ ret = ERR_PTR(dmabuf_imp_grant_foreign_access(gfns,
gntdev_dmabuf->u.imp.refs,
count, domid));
+ kfree(gfns);
if (IS_ERR(ret))
goto fail_end_access;

--
2.43.0