From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 16F473B1EC0; Thu, 17 Sep 2026 06:07:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789625251; cv=none; b=qMG/rgbCL/V0ahcNHamMdy19WtW7RtohSlVIjmAEtvRRA0J43/D76L+tCY8xgPVLv42J5LMnqjv0yJ74AkRJTLRLn49h9V5h62Jsbgt+wRTMyNiGzor/TJzJ4BFAHOLxf1BEJcUR4TsxV/xxrWAd5c1pIRfapHuazwi5+CMH5HA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789625251; c=relaxed/simple; bh=P6PUFpEezTXQyaWBIEtDNvZZzaChNobcfZ+Ac9hEUvs=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=cY2nQqxSa9DsBwcugKvAAoZLfPGL+DOYVlvTvO70q39qZ9PmWw2K04ANP0SiIztEGzEtw2vNO82ak+uSbGvuiFDrzX1qUJGon9Nw1cs19BBkESkTHsI9EblhIa4LGZAtHcP0L01JgwgX49hovAuwqcwar4m1G0NifzK7EhJ/A+Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JyWS//Ir; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="JyWS//Ir" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9C2571F000FF; Thu, 17 Sep 2026 06:07:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789625249; bh=gqaGXeiI19JmMrfZJKzFwEIp/5Qj6q2YW8WHfV2wLwo=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=JyWS//IrL4Aw7bFXomKjFolUgbIPHsZouDWnic5S+aTpPokzfuKgOWPTKof8kMzf4 ORUeYQ7na9GxLBhUgaS+QgFavTWYFpX9op1wkO371fVcu4TQB37YANueMbWoCS3a6P 4GaCJnXwuJRDcjIGL1Vgu+a09rYWHkz9cEJeKR8+50Jzg5GrQ848QBQVWuHm5hZT7F ErKPWyG7fMgo5Kj/NLgWhk9CRjoNVnq/glGzRCwnl+Wmj//5qEETRXIw2qdXzFNwkc JS3S0SAQC2GrQwKYZfkxkXqgQQolwcnUoslsEEN60If1un8fD41lNUq+qgIiSZzihh nUSPmRA2Mb7Ag== From: "Mike Rapoport (Microsoft)" Date: Thu, 17 Sep 2026 09:07:06 +0300 Subject: [PATCH 4/5] hibernation, KFENCE: explicitly map/unmap KFENCE pages Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260917-hibernation-v1-4-7f7dfae3dbe0@kernel.org> References: <20260917-hibernation-v1-0-7f7dfae3dbe0@kernel.org> In-Reply-To: <20260917-hibernation-v1-0-7f7dfae3dbe0@kernel.org> To: Andrew Morton , Alexander Potapenko , David Hildenbrand , Marco Elver , "Rafael J. Wysocki" Cc: Dmitry Vyukov , Len Brown , Mike Rapoport , Pavel Machek , kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-pm@vger.kernel.org X-Mailer: b4 0.16.1-dev The pages protected by KFENCE are removed from the direct map. safe_copy_page() temporarily maps and unmaps them using set_direct_map APIs, or, when the stars align, even using debug_pagealloc_map_pages(). Neither of these APIs cares whether it is a KFENCE page and both blindly perform the update of the kernel page table for any non-present page. Ability to use debug_pagealloc_map_pages() to remap KFENCE pages when both KFENCE and debug_pagealloc are enabled is an amusing coincidence. But with increasing appetite for using set_direct_map for hardening purposes, it becomes too big of a hammer to enable saving any non-present page in the hibernation image. Another gotcha is that loongarch that does not have a direct map at all advertises ARCH_HAS_SET_DIRECT_MAP to allow coexistence of KFENCE and hibernation. Extend KFENCE with a bitmap that tracks which pages are protected and provide kfence_force_mapping() and kfence_restore_mapping() APIs that allow forced mapping and unmapping of KFENCE pages. Use these APIs in hibernate_{map,unmap}_pages() for KFENCE pages. Signed-off-by: Mike Rapoport (Microsoft) --- include/linux/kfence.h | 29 +++++++++++++++++++++++++++ kernel/power/snapshot.c | 7 +++++++ mm/kfence/core.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++-- 3 files changed, 86 insertions(+), 2 deletions(-) diff --git a/include/linux/kfence.h b/include/linux/kfence.h index e5822f6e7f279..33a126cb6d1b7 100644 --- a/include/linux/kfence.h +++ b/include/linux/kfence.h @@ -222,6 +222,32 @@ struct kmem_obj_info; bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab); #endif +/** + * kfence_force_mapping() - make sure a KFENCE page is mapped + * @page: page to map + * + * Check whether @page is protected and map it if needed. + * + * Requires: is_kfence_address(page_address(page)) + * + * Return: + * * false - failed to map @page + * * true - @page is mapped + */ +bool kfence_force_mapping(struct page *page); + +/** + * kfence_restore_mapping() - restore mapping of a KFENCE page + * @page: page to restore mapping + * + * Requires: is_kfence_address(page_address(page)) + * + * Return: + * * false - failed to restore mapping of the @page + * * true - succeeded to restore mapping of the @page + */ +bool kfence_restore_mapping(struct page *page); + #else /* CONFIG_KFENCE */ #define kfence_sample_interval (0) @@ -241,6 +267,9 @@ static inline bool __must_check kfence_handle_page_fault(unsigned long addr, boo return false; } +static inline bool kfence_force_mapping(struct page *page) { return true; } +static inline bool kfence_restore_mapping(struct page *page) { return true; } + #ifdef CONFIG_PRINTK struct kmem_obj_info; static inline bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab) diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c index 52ef0599c2076..6583b57722e25 100644 --- a/kernel/power/snapshot.c +++ b/kernel/power/snapshot.c @@ -31,6 +31,7 @@ #include #include #include +#include #include #include @@ -81,6 +82,9 @@ static inline int hibernate_restore_unprotect_page(void *page_address) {return 0 static inline int hibernate_map_page(struct page *page) { + if (is_kfence_address(page_address(page))) + return kfence_force_mapping(page) ? 0 : -EFAULT; + if (IS_ENABLED(CONFIG_ARCH_HAS_SET_DIRECT_MAP)) { return set_direct_map_default_noflush(page, 1); } else { @@ -91,6 +95,9 @@ static inline int hibernate_map_page(struct page *page) static inline int hibernate_unmap_page(struct page *page) { + if (is_kfence_address(page_address(page))) + return kfence_restore_mapping(page) ? 0 : -EFAULT; + if (IS_ENABLED(CONFIG_ARCH_HAS_SET_DIRECT_MAP)) { unsigned long addr = (unsigned long)page_address(page); int ret = set_direct_map_invalid_noflush(page, 1); diff --git a/mm/kfence/core.c b/mm/kfence/core.c index 90925c646c4c2..666e8991d1fed 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -8,6 +8,7 @@ #define pr_fmt(fmt) "kfence: " fmt #include +#include #include #include #include @@ -123,6 +124,9 @@ module_param_named(check_on_panic, kfence_check_on_panic, bool, 0444); char *__kfence_pool __read_mostly; EXPORT_SYMBOL(__kfence_pool); /* Export for test modules. */ +/* keep track of protected pages */ +static DECLARE_BITMAP(kfence_protected_pages, KFENCE_POOL_SIZE / PAGE_SIZE); + /* * Per-object metadata, with one-to-one mapping of object metadata to * backing pages (in __kfence_pool). @@ -249,14 +253,36 @@ static bool alloc_covered_contains(u32 alloc_stack_hash) return true; } +static bool __kfence_protect(unsigned long addr, bool protect) +{ + unsigned long page_addr = ALIGN_DOWN(addr, PAGE_SIZE); + unsigned long pool_addr = (unsigned long)__kfence_pool; + unsigned long index = (page_addr - pool_addr) >> PAGE_SHIFT; + bool state; + + assign_bit(index, kfence_protected_pages, protect); + + /* + * Reapply protection if the desired state changed while updating + * the page table. + */ + do { + state = test_bit(index, kfence_protected_pages); + if (!kfence_protect_page(page_addr, state)) + return false; + } while (state != test_bit(index, kfence_protected_pages)); + + return true; +} + static bool kfence_protect(unsigned long addr) { - return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), true)); + return !KFENCE_WARN_ON(!__kfence_protect(addr, true)); } static bool kfence_unprotect(unsigned long addr) { - return !KFENCE_WARN_ON(!kfence_protect_page(ALIGN_DOWN(addr, PAGE_SIZE), false)); + return !KFENCE_WARN_ON(!__kfence_protect(addr, false)); } static inline unsigned long metadata_to_pageaddr(const struct kfence_metadata *meta) @@ -1335,3 +1361,25 @@ bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs return kfence_unprotect(addr); /* Unprotect and let access proceed. */ } + +bool kfence_force_mapping(struct page *page) +{ + unsigned long addr = (unsigned long)page_address(page); + unsigned long index = (addr - (unsigned long)__kfence_pool) >> PAGE_SHIFT; + + if (!test_bit(index, kfence_protected_pages)) + return true; + + return kfence_protect_page(addr, false); +} + +bool kfence_restore_mapping(struct page *page) +{ + unsigned long addr = (unsigned long)page_address(page); + unsigned long index = (addr - (unsigned long)__kfence_pool) >> PAGE_SHIFT; + + if (!test_bit(index, kfence_protected_pages)) + return true; + + return kfence_protect_page(addr, true); +} -- 2.53.0