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[PATCH 04/19] mm: assert that we preserve header vs region alignment


From: Daniel Axtens
Subject: [PATCH 04/19] mm: assert that we preserve header vs region alignment
Date: Tue, 12 Oct 2021 18:29:53 +1100

grub_mm_region_init() does:

  h = (grub_mm_header_t) (r + 1);

where h is a grub_mm_header_t and r is a grub_mm_region_t.

Cells are supposed to be GRUB_MM_ALIGN aligned, but while grub_mm_dump
ensures this vs the region header, grub_mm_region_init() does not.

It's better to be explicit than implicit here: rather than changing
grub_mm_region_init() to ALIGN_UP(), require that the struct is
explictly a multiple of the header size.

Signed-off-by: Daniel Axtens <dja@axtens.net>
---
 include/grub/mm_private.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/include/grub/mm_private.h b/include/grub/mm_private.h
index e80a059dd4e4..533b47173e18 100644
--- a/include/grub/mm_private.h
+++ b/include/grub/mm_private.h
@@ -20,6 +20,7 @@
 #define GRUB_MM_PRIVATE_H      1
 
 #include <grub/mm.h>
+#include <grub/misc.h>
 
 /* Magic words.  */
 #define GRUB_MM_FREE_MAGIC     0x2d3c2808
@@ -82,4 +83,11 @@ typedef struct grub_mm_region
 extern grub_mm_region_t EXPORT_VAR (grub_mm_base);
 #endif
 
+static inline void grub_mm_size_sanity_check(void) {
+  /* Ensure we preserve alignment when doing h = (grub_mm_header_t) (r + 1) */
+  COMPILE_TIME_ASSERT((sizeof(struct grub_mm_region) %
+                      sizeof(struct grub_mm_header)) == 0);
+
+}
+
 #endif
-- 
2.30.2




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