mm: fix struct page layout on 32-bit systems

commit 9ddb3c14afba8bc5950ed297f02d4ae05ff35cd1 upstream.

32-bit architectures which expect 8-byte alignment for 8-byte integers and
need 64-bit DMA addresses (arm, mips, ppc) had their struct page
inadvertently expanded in 2019.  When the dma_addr_t was added, it forced
the alignment of the union to 8 bytes, which inserted a 4 byte gap between
'flags' and the union.

Fix this by storing the dma_addr_t in one or two adjacent unsigned longs.
This restores the alignment to that of an unsigned long.  We always
store the low bits in the first word to prevent the PageTail bit from
being inadvertently set on a big endian platform.  If that happened,
get_user_pages_fast() racing against a page which was freed and
reallocated to the page_pool could dereference a bogus compound_head(),
which would be hard to trace back to this cause.

Link: https://lkml.kernel.org/r/20210510153211.1504886-1-willy@infradead.org
Fixes: c25fff7171be ("mm: add dma_addr_t to struct page")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Matteo Croce <mcroce@linux.microsoft.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 61c77cfff8c28db0265d0619cfddb01b4dbf8671..b4f85d8dd15e23d77fdcc9ca2980c9ed7b6ac3c0 100644 (file)
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -97,10 +97,10 @@ struct page {
                };
                struct {        /* page_pool used by netstack */
                        /**
-                        * @dma_addr: might require a 64-bit value even on
+                        * @dma_addr: might require a 64-bit value on
                         * 32-bit architectures.
                         */
-                       dma_addr_t dma_addr;
+                       unsigned long dma_addr[2];
                };
                struct {        /* slab, slob and slub */
                        union {

diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index b5b1953053468e5d627d122030ad77f50db51be7..e05744b9a1bc27d186625bb56c5cacbd14d61ea5 100644 (file)
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -198,7 +198,17 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
 
 static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
 {
-       return page->dma_addr;
+       dma_addr_t ret = page->dma_addr[0];
+       if (sizeof(dma_addr_t) > sizeof(unsigned long))
+               ret |= (dma_addr_t)page->dma_addr[1] << 16 << 16;
+       return ret;
+}
+
+static inline void page_pool_set_dma_addr(struct page *page, dma_addr_t addr)
+{
+       page->dma_addr[0] = addr;
+       if (sizeof(dma_addr_t) > sizeof(unsigned long))
+               page->dma_addr[1] = upper_32_bits(addr);
 }
 
 static inline bool is_page_pool_compiled_in(void)

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index f3c690b8c8e369b5ce355ab8d556d21c12b0631d..7c3c0774a67c7b9088b9e4291587249e04274871 100644 (file)
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -174,8 +174,10 @@ static void page_pool_dma_sync_for_device(struct page_pool *pool,
                                          struct page *page,
                                          unsigned int dma_sync_size)
 {
+       dma_addr_t dma_addr = page_pool_get_dma_addr(page);
+
        dma_sync_size = min(dma_sync_size, pool->p.max_len);
-       dma_sync_single_range_for_device(pool->p.dev, page->dma_addr,
+       dma_sync_single_range_for_device(pool->p.dev, dma_addr,
                                         pool->p.offset, dma_sync_size,
                                         pool->p.dma_dir);
 }
@@ -226,7 +228,7 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
                put_page(page);
                return NULL;
        }
-       page->dma_addr = dma;
+       page_pool_set_dma_addr(page, dma);
 
        if (pool->p.flags & PP_FLAG_DMA_SYNC_DEV)
                page_pool_dma_sync_for_device(pool, page, pool->p.max_len);
@@ -294,13 +296,13 @@ void page_pool_release_page(struct page_pool *pool, struct page *page)
                 */
                goto skip_dma_unmap;
 
-       dma = page->dma_addr;
+       dma = page_pool_get_dma_addr(page);
 
-       /* When page is unmapped, it cannot be returned our pool */
+       /* When page is unmapped, it cannot be returned to our pool */
        dma_unmap_page_attrs(pool->p.dev, dma,
                             PAGE_SIZE << pool->p.order, pool->p.dma_dir,
                             DMA_ATTR_SKIP_CPU_SYNC);
-       page->dma_addr = 0;
+       page_pool_set_dma_addr(page, 0);
 skip_dma_unmap:
        /* This may be the last page returned, releasing the pool, so
         * it is not safe to reference pool afterwards.