When commit 381295758792 ("dma-buf: system_heap: Rework system heap to
use sgtables instead of pagelists") stopped using heap_helpers.c and
added a custom system_heap_mmap(), the check rejecting private mappings
was dropped.
Other exporters and buffer allocators reject private or copy-on-write
mappings in their mmap handlers: cma_heap_mmap() and mmap_udmabuf()
check that VM_SHARED or VM_MAYSHARE is set, and drm_gem_shmem_mmap()
and ttm_bo_mmap_obj() reject vma_is_cow_mapping(vma).
However, system_heap_mmap() omits this check and calls remap_pfn_range()
even when userspace requests MAP_PRIVATE with PROT_WRITE. As a result,
subsequent CPU writes to a MAP_PRIVATE mapping of a system heap buffer
fault into do_wp_page() -> wp_page_copy(), silently allocating private
anonymous copy-on-write pages whose writes never reach the underlying
system heap buffer pages.
Reject non-shared mappings in system_heap_mmap() with -EINVAL to match
cma_heap_mmap() and mmap_udmabuf().
Fixes: 381295758792 ("dma-buf: system_heap: Rework system heap to use sgtables
instead of pagelists")
Cc: [email protected]
Signed-off-by: Chris Wiseman <[email protected]>
---
drivers/dma-buf/heaps/system_heap.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/dma-buf/heaps/system_heap.c
b/drivers/dma-buf/heaps/system_heap.c
index 1ef1bb3acbf1..f668dc8cb54a 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -235,6 +235,9 @@ static int system_heap_mmap(struct dma_buf *dmabuf, struct
vm_area_struct *vma)
pgprot_t prot;
int i, ret;
+ if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
+ return -EINVAL;
+
prot = vma->vm_page_prot;
if (cc_shared_buffer(buffer))
prot = pgprot_decrypted(prot);
--
2.56.0.317.g454f8302e1-goog
