From: "Matthew Wilcox (Oracle)" willy@infradead.org Subject: mm: fix struct page layout on 32-bit systems

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 ---

include/linux/mm_types.h | 4 ++-- include/net/page_pool.h | 12 +++++++++++- net/core/page_pool.c | 12 +++++++----- 3 files changed, 20 insertions(+), 8 deletions(-)

--- a/include/linux/mm_types.h~mm-fix-struct-page-layout-on-32-bit-systems +++ a/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 { --- a/include/net/page_pool.h~mm-fix-struct-page-layout-on-32-bit-systems +++ a/include/net/page_pool.h @@ -198,7 +198,17 @@ static inline void page_pool_recycle_dir

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) --- a/net/core/page_pool.c~mm-fix-struct-page-layout-on-32-bit-systems +++ a/net/core/page_pool.c @@ -174,8 +174,10 @@ static void page_pool_dma_sync_for_devic 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); } @@ -195,7 +197,7 @@ static bool page_pool_dma_map(struct pag if (dma_mapping_error(pool->p.dev, dma)) return false;

- 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); @@ -331,13 +333,13 @@ void page_pool_release_page(struct 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. _