[PATCH] cma: check for memory region overlapping

[Binglei Wang]

From: Binglei Wang <l3b2w1@xxxxxxxxx>

Cma memory region editted carelessly in dts may overlap
with kernel code/data memory region which is reserved by memblock
during the early phase of system memory initialization.

Without checking overlap and cma area setup done,
this region will be released to buddy system later.

When memory usage under pressure, memory allocated from
this region will collide with kernel code which is read-only.
And the following writing to this region will trigger the panic
of writing to read-only memory.

So when rmem_cma_setup returns EBUSY, do not phys-free this region
to memblock or else we end up with free the kernel code memory
to buddy system.

Signed-off-by: Binglei Wang <l3b2w1@xxxxxxxxx>
---
 drivers/of/of_reserved_mem.c | 3 ---
 kernel/dma/contiguous.c      | 5 +++++
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
index 7ec94cfcb..d62cc76ef 100644
--- a/drivers/of/of_reserved_mem.c
+++ b/drivers/of/of_reserved_mem.c
@@ -338,9 +338,6 @@ void __init fdt_init_reserved_mem(void)
 					rmem->name);
 				if (nomap)
 					memblock_clear_nomap(rmem->base, rmem->size);
-				else
-					memblock_phys_free(rmem->base,
-							   rmem->size);
 			} else {
 				phys_addr_t end = rmem->base + rmem->size - 1;
 				bool reusable =
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 6ea80ae42..a349f3e97 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -410,6 +410,11 @@ static int __init rmem_cma_setup(struct reserved_mem *rmem)
 		return -EBUSY;
 	}
 
+	if (memblock_is_region_reserved(rmem->base, rmem->size)) {
+		pr_info("Reserved memory: overlap with exsiting one\n");
+		return -EBUSY;
+	}
+
 	if (!of_get_flat_dt_prop(node, "reusable", NULL) ||
 	    of_get_flat_dt_prop(node, "no-map", NULL))
 		return -EINVAL;
-- 
2.34.1