The patch titled Subject: /proc/kpageflags: do not use uninitialized struct pages has been added to the -mm tree. Its filename is proc-kpageflags-do-not-use-uninitialized-struct-pages.patch

This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/proc-kpageflags-do-not-use-uninitia... and later at http://ozlabs.org/~akpm/mmotm/broken-out/proc-kpageflags-do-not-use-uninitia...

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------------------------------------------------------ From: Toshiki Fukasawa t-fukasawa@vx.jp.nec.com Subject: /proc/kpageflags: do not use uninitialized struct pages

A kernel panic was observed during reading /proc/kpageflags for first few pfns allocated by pmem namespace:

BUG: unable to handle page fault for address: fffffffffffffffe [ 114.495280] #PF: supervisor read access in kernel mode [ 114.495738] #PF: error_code(0x0000) - not-present page [ 114.496203] PGD 17120e067 P4D 17120e067 PUD 171210067 PMD 0 [ 114.496713] Oops: 0000 [#1] SMP PTI [ 114.497037] CPU: 9 PID: 1202 Comm: page-types Not tainted 5.3.0-rc1 #1 [ 114.497621] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org 04/01/2014 [ 114.498706] RIP: 0010:stable_page_flags+0x27/0x3f0 [ 114.499142] Code: 82 66 90 66 66 66 66 90 48 85 ff 0f 84 d1 03 00 00 41 54 55 48 89 fd 53 48 8b 57 08 48 8b 1f 48 8d 42 ff 83 e2 01 48 0f 44 c7 <48> 8b 00 f6 c4 02 0f 84 57 03 00 00 45 31 e4 48 8b 55 08 48 89 ef [ 114.500788] RSP: 0018:ffffa5e601a0fe60 EFLAGS: 00010202 [ 114.501373] RAX: fffffffffffffffe RBX: ffffffffffffffff RCX: 0000000000000000 [ 114.502009] RDX: 0000000000000001 RSI: 00007ffca13a7310 RDI: ffffd07489000000 [ 114.502637] RBP: ffffd07489000000 R08: 0000000000000001 R09: 0000000000000000 [ 114.503270] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000240000 [ 114.503896] R13: 0000000000080000 R14: 00007ffca13a7310 R15: ffffa5e601a0ff08 [ 114.504530] FS: 00007f0266c7f540(0000) GS:ffff962dbbac0000(0000) knlGS:0000000000000000 [ 114.505245] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 114.505754] CR2: fffffffffffffffe CR3: 000000023a204000 CR4: 00000000000006e0 [ 114.506401] Call Trace: [ 114.506660] kpageflags_read+0xb1/0x130 [ 114.507051] proc_reg_read+0x39/0x60 [ 114.507387] vfs_read+0x8a/0x140 [ 114.507686] ksys_pread64+0x61/0xa0 [ 114.508021] do_syscall_64+0x5f/0x1a0 [ 114.508372] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 114.508844] RIP: 0033:0x7f0266ba426b

The reason for the panic is that stable_page_flags() which parses the page flags uses uninitialized struct pages reserved by the ZONE_DEVICE driver.

Earlier approach to fix this was discussed here: https://marc.info/?l=linux-mm&m=152964770000672&w=2

This is another approach. To avoid using the uninitialized struct page, immediately return with KPF_RESERVED at the beginning of stable_page_flags() if the page is reserved by ZONE_DEVICE driver.

Link: http://lkml.kernel.org/r/20190725023100.31141-3-t-fukasawa@vx.jp.nec.com Signed-off-by: Toshiki Fukasawa t-fukasawa@vx.jp.nec.com Cc: Alexey Dobriyan adobriyan@gmail.com Cc: Christoph Hellwig hch@lst.de Cc: Dan Williams dan.j.williams@intel.com Cc: Junichi Nomura j-nomura@ce.jp.nec.com Cc: Michal Hocko mhocko@kernel.org Cc: Naoya Horiguchi n-horiguchi@ah.jp.nec.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

fs/proc/page.c | 3 +++ include/linux/memremap.h | 6 ++++++ kernel/memremap.c | 20 ++++++++++++++++++++ 3 files changed, 29 insertions(+)

--- a/fs/proc/page.c~proc-kpageflags-do-not-use-uninitialized-struct-pages +++ a/fs/proc/page.c @@ -97,6 +97,9 @@ u64 stable_page_flags(struct page *page) if (!page) return BIT_ULL(KPF_NOPAGE);

+ if (pfn_zone_device_reserved(page_to_pfn(page))) + return BIT_ULL(KPF_RESERVED); + k = page->flags; u = 0;

--- a/include/linux/memremap.h~proc-kpageflags-do-not-use-uninitialized-struct-pages +++ a/include/linux/memremap.h @@ -124,6 +124,7 @@ static inline struct vmem_altmap *pgmap_ }

#ifdef CONFIG_ZONE_DEVICE +bool pfn_zone_device_reserved(unsigned long pfn); void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap); void devm_memunmap_pages(struct device *dev, struct dev_pagemap *pgmap); struct dev_pagemap *get_dev_pagemap(unsigned long pfn, @@ -132,6 +133,11 @@ struct dev_pagemap *get_dev_pagemap(unsi unsigned long vmem_altmap_offset(struct vmem_altmap *altmap); void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pfns); #else +static inline bool pfn_zone_device_reserved(unsigned long pfn) +{ + return false; +} + static inline void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap) { --- a/kernel/memremap.c~proc-kpageflags-do-not-use-uninitialized-struct-pages +++ a/kernel/memremap.c @@ -72,6 +72,26 @@ static unsigned long pfn_next(unsigned l return pfn + 1; }

+/* + * This returns true if the page is reserved by ZONE_DEVICE driver. + */ +bool pfn_zone_device_reserved(unsigned long pfn) +{ + struct dev_pagemap *pgmap; + struct vmem_altmap *altmap; + bool ret = false; + + pgmap = get_dev_pagemap(pfn, NULL); + if (!pgmap) + return ret; + altmap = pgmap_altmap(pgmap); + if (altmap && pfn < (altmap->base_pfn + altmap->reserve)) + ret = true; + put_dev_pagemap(pgmap); + + return ret; +} + #define for_each_device_pfn(pfn, map) \ for (pfn = pfn_first(map); pfn < pfn_end(map); pfn = pfn_next(pfn))

_

Patches currently in -mm which might be from t-fukasawa@vx.jp.nec.com are

proc-kpageflags-prevent-an-integer-overflow-in-stable_page_flags.patch proc-kpageflags-do-not-use-uninitialized-struct-pages.patch