[PATCH] cma: fail if fixed declaration can't be honored

[Doug Berger]

The description of the cma_declare_contiguous() function indicates
that if the 'fixed' argument is true the reserved contiguous area
must be exactly at the address of the 'base' argument.

However, the function currently allows the 'base', 'size', and
'limit' arguments to be silently adjusted to meet alignment
constraints. This commit enforces the documented behavior through
explicit checks that return an error if the region does not fit
within a specified region.

Fixes: 5ea3b1b2f8ad ("cma: add placement specifier for "cma=" kernel parameter")
Signed-off-by: Doug Berger <opendmb@xxxxxxxxx>
---
 mm/cma.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/mm/cma.c b/mm/cma.c
index 3340ef34c154..4973d253dc83 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -278,6 +278,12 @@ int __init cma_declare_contiguous(phys_addr_t base,
 	 */
 	alignment = max(alignment,  (phys_addr_t)PAGE_SIZE <<
 			  max_t(unsigned long, MAX_ORDER - 1, pageblock_order));
+	if (fixed && base & (alignment - 1)) {
+		ret = -EINVAL;
+		pr_err("Region at %pa must be aligned to %pa bytes\n",
+			&base, &alignment);
+		goto err;
+	}
 	base = ALIGN(base, alignment);
 	size = ALIGN(size, alignment);
 	limit &= ~(alignment - 1);
@@ -308,6 +314,13 @@ int __init cma_declare_contiguous(phys_addr_t base,
 	if (limit == 0 || limit > memblock_end)
 		limit = memblock_end;
 
+	if (base + size > limit) {
+		ret = -EINVAL;
+		pr_err("Size (%pa) of region at %pa exceeds limit (%pa)\n",
+			&size, &base, &limit);
+		goto err;
+	}
+
 	/* Reserve memory */
 	if (fixed) {
 		if (memblock_is_region_reserved(base, size) ||
-- 
2.7.4