From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 71457CAC59A for ; Wed, 17 Sep 2025 12:57:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=rysuZTNXGlhJ/pNo9I//zN6bxCAYHhYiKx0dmE9O/jQ=; b=3le4lZaSwTsa13RHQgr6rTFy67 geEdD0ucamVsJ3+PHXrQFNzlrGneCGqZeUvRnytPMSDqGm9695vQVQxtvewzRvlDwIYyyKWtiXZgd u7w+HyuG0bo+TxUOyfwMTlewc40OnRHez9dArxlGzRCdXpplqCOq9cosBjFHBFY6iq25XbOnudyFa 9smoxmJx37KFjfmdLYEVrUjwJy7hUBt5AwvJPpwcPK+rZTFk5daZ6nkcPnhukDQWbYGCK8JYhXhWx bkA97M4UTGx6zlUR7/aX7HFvtNGx9CveDqJRCM8H8tzN1b6h7CfCFHASWaMLYkiQkg8iqKAJ9ih8I 9+cbbrXQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uyrjC-0000000BToD-0O4y; Wed, 17 Sep 2025 12:57:42 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1uyrj9-0000000BTmg-2TJY for kexec@lists.infradead.org; Wed, 17 Sep 2025 12:57:40 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 4B05C44E68; Wed, 17 Sep 2025 12:57:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 707FEC4CEFA; Wed, 17 Sep 2025 12:57:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758113859; bh=r+p/fW1qMMIwpqKIwYaP72h2rsOOsXIYd5AWK52PFjM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=MDhxPTlLBJEX7J3Lii/V9VX413VtE8eVKCNeBKb26X7SilRFKRMeS6RdKznIrZIwd 2mLPCzdmU41qnSN6vZ8XmntqKfRPB5hie55/t133keMIx5R0WSDyoxoBa5PYQHa+DQ bS9al/X6rX1zlUQVFoHb2Jy7zSiDRVGyOHLvPX8WDleZw1R5t2KlSKU8NRCCzqyqjt 5mmwc8Ymr+ZlrYQ039KVM7csj2grE2DOVORw1MpBZjs+VzdwvGmfeRs6AQd52RfqXq WSJd2tVRXZyqY808XSja7d79EhFySiEkJ6BjBW8MTcFVCDSEzQuEfWTMeSz/go9twm i9+PHR6yWbvxw== From: Pratyush Yadav To: Alexander Graf , Mike Rapoport , Changyuan Lyu , Andrew Morton , Baoquan He , Pratyush Yadav , Pasha Tatashin , Jason Gunthorpe , Chris Li , Jason Miu Cc: linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org Subject: [PATCH v2 2/2] kho: make sure page being restored is actually from KHO Date: Wed, 17 Sep 2025 14:56:54 +0200 Message-ID: <20250917125725.665-2-pratyush@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250917125725.665-1-pratyush@kernel.org> References: <20250917125725.665-1-pratyush@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250917_055739_665921_66616559 X-CRM114-Status: GOOD ( 20.15 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org When restoring a page, no sanity checks are done to make sure the page actually came from a kexec handover. The caller is trusted to pass in the right address. If the caller has a bug and passes in a wrong address, an in-use page might be "restored" and returned, causing all sorts of memory corruption. Harden the page restore logic by stashing in a magic number in page->private along with the order. If the magic number does not match, the page won't be touched. page->private is an unsigned long. The union kho_page_info splits it into two parts, with one holding the order and the other holding the magic number. Signed-off-by: Pratyush Yadav --- Notes: Changes in v2: - Add a WARN_ON_ONCE() if order or magic is invalid. - Add a comment explaining why the magic check also implicitly makes sure phys is order-aligned. - Clear page private to make sure later restores of the same page error out. - Move the checks to kho_restore_page() since patch 1 now moves sanity checking to it. kernel/kexec_handover.c | 41 ++++++++++++++++++++++++++++++++++------- 1 file changed, 34 insertions(+), 7 deletions(-) diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c index 69cab82abaaef..911fda8532b2e 100644 --- a/kernel/kexec_handover.c +++ b/kernel/kexec_handover.c @@ -32,6 +32,22 @@ #define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map" #define PROP_SUB_FDT "fdt" +#define KHO_PAGE_MAGIC 0x4b484f50U /* ASCII for 'KHOP' */ + +/* + * KHO uses page->private, which is an unsigned long, to store page metadata. + * Use it to store both the magic and the order. + */ +union kho_page_info { + unsigned long page_private; + struct { + unsigned int order; + unsigned int magic; + }; +}; + +static_assert(sizeof(union kho_page_info) == sizeof(((struct page *)0)->private)); + static bool kho_enable __ro_after_init; bool kho_is_enabled(void) @@ -186,16 +202,24 @@ static int __kho_preserve_order(struct kho_mem_track *track, unsigned long pfn, static struct page *kho_restore_page(phys_addr_t phys) { struct page *page = pfn_to_online_page(PHYS_PFN(phys)); - unsigned int nr_pages, order; + union kho_page_info info; + unsigned int nr_pages; if (!page) return NULL; - order = page->private; - if (order > MAX_PAGE_ORDER) + info.page_private = page->private; + /* + * deserialize_bitmap() only sets the magic on the head page. This magic + * check also implicitly makes sure phys is order-aligned since for + * non-order-aligned phys addresses, magic will never be set. + */ + if (WARN_ON_ONCE(info.magic != KHO_PAGE_MAGIC || info.order > MAX_PAGE_ORDER)) return NULL; - nr_pages = (1 << order); + nr_pages = (1 << info.order); + /* Clear private to make sure later restores on this page error out. */ + page->private = 0; /* Head page gets refcount of 1. */ set_page_count(page, 1); @@ -203,8 +227,8 @@ static struct page *kho_restore_page(phys_addr_t phys) for (unsigned int i = 1; i < nr_pages; i++) set_page_count(page + i, 0); - if (order > 0) - prep_compound_page(page, order); + if (info.order > 0) + prep_compound_page(page, info.order); adjust_managed_page_count(page, nr_pages); return page; @@ -341,10 +365,13 @@ static void __init deserialize_bitmap(unsigned int order, phys_addr_t phys = elm->phys_start + (bit << (order + PAGE_SHIFT)); struct page *page = phys_to_page(phys); + union kho_page_info info; memblock_reserve(phys, sz); memblock_reserved_mark_noinit(phys, sz); - page->private = order; + info.magic = KHO_PAGE_MAGIC; + info.order = order; + page->private = info.page_private; } } -- 2.47.3