[PATCH AUTOSEL 5.10 6/7] xen/gntdev: Fix the abuse of underlying struct page in DMA-buf import

[Sasha Levin <sashal@xxxxxxxxxx>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

[ 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@xxxxxxxx>
Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
Acked-by: Christian König <christian.koenig@xxxxxxx>
Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Acked-by: Daniel Vetter <daniel@xxxxxxxx>
Link: https://lore.kernel.org/r/20240107103426.2038075-1-olekstysh@xxxxxxxxx
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 4c13cbc99896..398ea69c176c 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>
@@ -56,7 +57,7 @@ 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;
 };
 
@@ -490,7 +491,7 @@ 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;
@@ -513,7 +514,7 @@ 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;
        }
 
@@ -535,7 +536,6 @@ 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);
 }
@@ -555,12 +555,6 @@ 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++)
@@ -582,7 +576,8 @@ 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);
@@ -630,26 +625,31 @@ 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