6.12-stable review patch. If anyone has any objections, please let me know.
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From: Matthew Wilcox (Oracle) willy@infradead.org
commit 4de22b2a6a7477d84d9a01eb6b62a9117309d722 upstream.
It is unsafe to call PageTail() in dump_page() as page_is_fake_head() will almost certainly return true when called on a head page that is copied to the stack. That will cause the VM_BUG_ON_PGFLAGS() in const_folio_flags() to trigger when it shouldn't. Fortunately, we don't need to call PageTail() here; it's fine to have a pointer to a virtual alias of the page's flag word rather than the real page's flag word.
Link: https://lkml.kernel.org/r/20241125201721.2963278-1-willy@infradead.org Fixes: fae7d834c43c ("mm: add __dump_folio()") Signed-off-by: Matthew Wilcox (Oracle) willy@infradead.org Cc: Kees Cook kees@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/page-flags.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -306,7 +306,7 @@ static const unsigned long *const_folio_ { const struct page *page = &folio->page;
- VM_BUG_ON_PGFLAGS(PageTail(page), page); + VM_BUG_ON_PGFLAGS(page->compound_head & 1, page); VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags), page); return &page[n].flags; } @@ -315,7 +315,7 @@ static unsigned long *folio_flags(struct { struct page *page = &folio->page;
- VM_BUG_ON_PGFLAGS(PageTail(page), page); + VM_BUG_ON_PGFLAGS(page->compound_head & 1, page); VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags), page); return &page[n].flags; }