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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tCu96-00000002bHi-1PCb; Mon, 18 Nov 2024 05:17:56 +0000 Date: Mon, 18 Nov 2024 05:17:56 +0000 From: Matthew Wilcox To: Kees Cook Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] mm: Handle compound pages better in __dump_page() Message-ID: References: <20241117055243.work.907-kees@kernel.org> <202411172043.C19A3963@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202411172043.C19A3963@keescook> X-Stat-Signature: pzqo5ff897a7myiecqggg9sfj8u835fp X-Rspamd-Queue-Id: D5FE21C0005 X-Rspamd-Server: rspam08 X-Rspam-User: X-HE-Tag: 1731907017-920526 X-HE-Meta: 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 o+f6jOhE FLjFaKF+uJrEeqfdSKGpGXfO3wBqOUE5QMpSewZYzQWdVsem2lQbN3wPHgKAfgCqxbfJe0aGdkzOdsz1YTVbgtbeMN84ZnDIrfYxj1iqnimFVfZo6EqA5IOFxevPmTJIIALpI6W8SU286QlwYlFILfKbAQgFYxAIjzr8EcQUGwSR6khzVIz+x8dmhIqGc2Hg0PXmX7B9x9pRvgriOYXMKftBvY5doKVMxsfKy+PPrwCLHjtySjv+uy01tGv4HJVuxj2oUngOEgRR0Z2oGTglhGbOOVQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000035, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Nov 17, 2024 at 08:46:45PM -0800, Kees Cook wrote: > On Mon, Nov 18, 2024 at 04:10:52AM +0000, Matthew Wilcox wrote: > > folio_test_large() does not touch page[1]. Look: > > It does, though. :( It's via the PageTail(), which calls page_is_fake_head(): Oh. It shouldn't; that's unnecessary. +++ b/include/linux/page-flags.h @@ -306,7 +306,7 @@ static const unsigned long *const_folio_flags(const struct folio *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 folio *folio, unsigned n) { 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; } should fix that.