[PATCH v4 24/38] mm/vma: enforce that mm-managed mappings may not set VMA_IO_BIT

[Lorenzo Stoakes (ARM)]

It makes no sense for a mapping whose contents the kernel does not own to
specify that the range is MMIO.

Prior to this patch, all in-tree drivers which did so have been updated
such that they are marked as not being mm-managed. The check WARNs and
fails the mmap for any out-of-tree driver that still sets VMA_IO_BIT
without a kernel mapping.

No functional change intended for in-tree code.

Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
---
 mm/vma.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/vma.c b/mm/vma.c
index df2efdfa3805..43d32c3b8f6b 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -2793,6 +2793,12 @@ static int mmap_validate_vma_flags(const vma_flags_t *flags)
 		return -EINVAL;
 #endif
 
+	if (!vma_flags_test_any(flags, VMA_PFNMAP_BIT, VMA_MIXEDMAP_BIT)) {
+		/* mm-managed mappings may not set VMA_IO_BIT. */
+		if (WARN_ON_ONCE(vma_flags_test(flags, VMA_IO_BIT)))
+			return -EINVAL;
+	}
+
 	return 0;
 }
 

-- 
2.55.0