GCC 15's -Warray-bounds reports:
In function 'page_fixed_fake_head',
inlined from '_compound_head' at ../include/linux/page-flags.h:251:24,
inlined from '__dump_page' at ../mm/debug.c:123:11:
../include/asm-generic/rwonce.h:44:26: warning: array subscript 9 is outside array bounds of 'struct page[1]' [-Warray-bounds=]
(Not noted in this warning is that the code passes through page_folio()
_Generic macro.)
It may not be that "precise" is always 1 page, so accessing "page[1]"
in either page_folio() or folio_test_large() may cause problems.
Instead, explicitly make precise 2 pages. Just open-coding page_folio()
isn't sufficient to avoid the warning[1].
Link: https://lore.kernel.org/r/ZkN0aSE9zAB5aXvM@xxxxxxxxxxxxxxxxxxxx [1]
Signed-off-by: Kees Cook <kees@xxxxxxxxxx>
---
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
---
mm/debug.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/mm/debug.c b/mm/debug.c
index aa57d3ffd4ed..7ea396e8c143 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -123,15 +123,15 @@ static void __dump_folio(struct folio *folio, struct page *page,
static void __dump_page(const struct page *page)
{
struct folio *foliop, folio;
- struct page precise;
+ struct page precise[2] = { };
unsigned long pfn = page_to_pfn(page);
unsigned long idx, nr_pages = 1;
int loops = 5;
again:
- memcpy(&precise, page, sizeof(*page));
- foliop = page_folio(&precise);
- if (foliop == (struct folio *)&precise) {
+ memcpy(&precise[0], page, sizeof(*page));
+ foliop = page_folio(&precise[0]);
+ if (foliop == (struct folio *)&precise[0]) {
idx = 0;
if (!folio_test_large(foliop))
goto dump;
@@ -150,13 +150,13 @@ static void __dump_page(const struct page *page)
if (loops-- > 0)
goto again;
pr_warn("page does not match folio\n");
- precise.compound_head &= ~1UL;
- foliop = (struct folio *)&precise;
+ precise[0].compound_head &= ~1UL;
+ foliop = (struct folio *)&precise[0];
idx = 0;
}
dump:
- __dump_folio(foliop, &precise, pfn, idx);
+ __dump_folio(foliop, &precise[0], pfn, idx);
}
void dump_page(const struct page *page, const char *reason)
--
2.34.1
