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Wed, 9 Oct 2019 10:20:04 +0000 (UTC) Received: from [10.36.116.112] (ovpn-116-112.ams2.redhat.com [10.36.116.112]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9A0D460BF4; Wed, 9 Oct 2019 10:20:00 +0000 (UTC) Subject: Re: [PATCH v1] mm: Fix access of uninitialized memmaps in fs/proc/page.c To: Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Qian Cai , Alexey Dobriyan , Naoya Horiguchi , Andrew Morton , Stephen Rothwell , Toshiki Fukasawa , Konstantin Khlebnikov , Mike Rapoport , Anthony Yznaga , Jason Gunthorpe , Dan Williams , Logan Gunthorpe , Ira Weiny , "Aneesh Kumar K.V" , linux-fsdevel@vger.kernel.org References: <20191009091205.11753-1-david@redhat.com> <20191009093756.GV6681@dhcp22.suse.cz> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwX4EEwECACgFAljj9eoCGwMFCQlmAYAGCwkI BwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEE3eEPcA/4Na5IIP/3T/FIQMxIfNzZshIq687qgG 8UbspuE/YSUDdv7r5szYTK6KPTlqN8NAcSfheywbuYD9A4ZeSBWD3/NAVUdrCaRP2IvFyELj xoMvfJccbq45BxzgEspg/bVahNbyuBpLBVjVWwRtFCUEXkyazksSv8pdTMAs9IucChvFmmq3 jJ2vlaz9lYt/lxN246fIVceckPMiUveimngvXZw21VOAhfQ+/sofXF8JCFv2mFcBDoa7eYob s0FLpmqFaeNRHAlzMWgSsP80qx5nWWEvRLdKWi533N2vC/EyunN3HcBwVrXH4hxRBMco3jvM m8VKLKao9wKj82qSivUnkPIwsAGNPdFoPbgghCQiBjBe6A75Z2xHFrzo7t1jg7nQfIyNC7ez MZBJ59sqA9EDMEJPlLNIeJmqslXPjmMFnE7Mby/+335WJYDulsRybN+W5rLT5aMvhC6x6POK z55fMNKrMASCzBJum2Fwjf/VnuGRYkhKCqqZ8gJ3OvmR50tInDV2jZ1DQgc3i550T5JDpToh dPBxZocIhzg+MBSRDXcJmHOx/7nQm3iQ6iLuwmXsRC6f5FbFefk9EjuTKcLMvBsEx+2DEx0E UnmJ4hVg7u1PQ+2Oy+Lh/opK/BDiqlQ8Pz2jiXv5xkECvr/3Sv59hlOCZMOaiLTTjtOIU7Tq 7ut6OL64oAq+zsFNBFXLn5EBEADn1959INH2cwYJv0tsxf5MUCghCj/CA/lc/LMthqQ773ga uB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+neKHUCBtHyseBfDXHA6m4B3mUTWo13nid 0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNroXcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X 2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+ xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVpAfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC 8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0GpzFXT7enwyvFFFyAS0Nk1q/7EChPcbRb hJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkC u8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUAlpmrzk/bLbRkF3TwgucpyPtcpmQtTkWS gDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQUF1nl4SSPV0LLH63+BrrHasfJzxKXzqg rW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3qKe7ofum3s4vq7oFCPsOgwARAQABwsFl BBgBAgAPBQJVy5+RAhsMBQkJZgGAAAoJEE3eEPcA/4NagOsP/jPoIBb/iXVbM+fmSHOjEshl KMwEl/m5iLj3iHnHPVLBUWrXPdS7iQijJA/VLxjnFknhaS60hkUNWexDMxVVP/6lbOrs4bDZ NEWDMktAeqJaFtxackPszlcpRVkAs6Msn9tu8hlvB517pyUgvuD7ZS9gGOMmYwFQDyytpepo YApVV00P0u3AaE0Cj/o71STqGJKZxcVhPaZ+LR+UCBZOyKfEyq+ZN311VpOJZ1IvTExf+S/5 lqnciDtbO3I4Wq0ArLX1gs1q1XlXLaVaA3yVqeC8E7kOchDNinD3hJS4OX0e1gdsx/e6COvy qNg5aL5n0Kl4fcVqM0LdIhsubVs4eiNCa5XMSYpXmVi3HAuFyg9dN+x8thSwI836FoMASwOl C7tHsTjnSGufB+D7F7ZBT61BffNBBIm1KdMxcxqLUVXpBQHHlGkbwI+3Ye+nE6HmZH7IwLwV W+Ajl7oYF+jeKaH4DZFtgLYGLtZ1LDwKPjX7VAsa4Yx7S5+EBAaZGxK510MjIx6SGrZWBrrV TEvdV00F2MnQoeXKzD7O4WFbL55hhyGgfWTHwZ457iN9SgYi1JLPqWkZB0JRXIEtjd4JEQcx +8Umfre0Xt4713VxMygW0PnQt5aSQdMD58jHFxTk092mU+yIHj5LeYgvwSgZN4airXk5yRXl SE+xAvmumFBY Organization: Red Hat GmbH Message-ID: <67aeaacc-d850-5c81-bd17-e95c7f7f75df@redhat.com> Date: Wed, 9 Oct 2019 12:19:59 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20191009093756.GV6681@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Wed, 09 Oct 2019 10:20:04 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 09.10.19 11:37, Michal Hocko wrote: > On Wed 09-10-19 11:12:04, David Hildenbrand wrote: >> There are various places where we access uninitialized memmaps, namely= : >> - /proc/kpagecount >> - /proc/kpageflags >> - /proc/kpagecgroup >> - memory_failure() - which reuses stable_page_flags() from fs/proc/pag= e.c >> >> We have initialized memmaps either when the section is online or when >> the page was initialized to the ZONE_DEVICE. Uninitialized memmaps con= tain >> garbage and in the worst case trigger kernel BUGs, especially with >> CONFIG_PAGE_POISONING. >> >> For example, not onlining a DIMM during boot and calling /proc/kpageco= unt >> with CONFIG_PAGE_POISONING: >> :/# cat /proc/kpagecount > tmp.test >> [ 95.600592] BUG: unable to handle page fault for address: fffffffff= ffffffe >> [ 95.601238] #PF: supervisor read access in kernel mode >> [ 95.601675] #PF: error_code(0x0000) - not-present page >> [ 95.602116] PGD 114616067 P4D 114616067 PUD 114618067 PMD 0 >> [ 95.602596] Oops: 0000 [#1] SMP NOPTI >> [ 95.602920] CPU: 0 PID: 469 Comm: cat Not tainted 5.4.0-rc1-next-20= 191004+ #11 >> [ 95.603547] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), = BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.4 >> [ 95.604521] RIP: 0010:kpagecount_read+0xce/0x1e0 >> [ 95.604917] Code: e8 09 83 e0 3f 48 0f a3 02 73 2d 4c 89 e7 48 c1 e= 7 06 48 03 3d ab 51 01 01 74 1d 48 8b 57 08 480 >> [ 95.606450] RSP: 0018:ffffa14e409b7e78 EFLAGS: 00010202 >> [ 95.606904] RAX: fffffffffffffffe RBX: 0000000000020000 RCX: 000000= 0000000000 >> [ 95.607519] RDX: 0000000000000001 RSI: 00007f76b5595000 RDI: fffff3= 5645000000 >> [ 95.608128] RBP: 00007f76b5595000 R08: 0000000000000001 R09: 000000= 0000000000 >> [ 95.608731] R10: 0000000000000000 R11: 0000000000000000 R12: 000000= 0000140000 >> [ 95.609327] R13: 0000000000020000 R14: 00007f76b5595000 R15: ffffa1= 4e409b7f08 >> [ 95.609924] FS: 00007f76b577d580(0000) GS:ffff8f41bd400000(0000) k= nlGS:0000000000000000 >> [ 95.610599] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [ 95.611083] CR2: fffffffffffffffe CR3: 0000000078960000 CR4: 000000= 00000006f0 >> [ 95.611686] Call Trace: >> [ 95.611906] proc_reg_read+0x3c/0x60 >> [ 95.612228] vfs_read+0xc5/0x180 >> [ 95.612505] ksys_read+0x68/0xe0 >> [ 95.612785] do_syscall_64+0x5c/0xa0 >> [ 95.613092] entry_SYSCALL_64_after_hwframe+0x49/0xbe >> >> Note that there are still two possible races as far as I can see: >> - pfn_to_online_page() succeeding but the memory getting offlined and >> removed. get_online_mems() could help once we run into this. >> - pfn_zone_device() succeeding but the memmap not being fully >> initialized yet. As the memmap is initialized outside of the memory >> hoptlug lock, get_online_mems() can't help. >> >> Let's keep the existing interfaces working with ZONE_DEVICE memory. We >> can later come back and fix these rare races and eventually speed-up t= he >> ZONE_DEVICE detection. This patch now also makes sure we don't dump da= ta >> about memory blocks that are already offline again. >=20 > As I've already expressed already I am not really happy to have explici= t > checks for zone device pages in pfn walkers. This is simply too fragile= . >=20 > pfn_to_online_page makes sense because offline pages are not really in = a > defined state. This would be worth a patch of its own. I remember there The issue is, once I check for pfn_to_online_page(), these functions can't handle ZONE_DEVICE at all anymore. Especially in regards to memory_failure() I don't think this is acceptable. So while I (personally) only care about adding pfn_to_online_page() checks, the in-this-sense-fragile-subsection ZONE_DEVICE implementation requires me to introduce a temporary check for initialized memmaps. > was a discussion about the uninitialized zone device memmaps. It would > be really good to summarize this discussion in the changelog and > conclude why the explicit check is really good and what were other > alternatives considered. Yeah, I also expressed my feelings and the issues to be solved by ZONE_DEVICE people in https://lkml.org/lkml/2019/9/6/114. However, the discussion stalled and nobody really proposed a solution or followed up. I want to have this fixed now, as it is much easier to trigger with "[PATCH v6 00/10] mm/memory_hotplug: Shrink zones before removing memory" for !ZONE_DEVICE. As we already do have a similar check (pfn_zone_device_reserved()) that I merely convert for now, I will summarize and make it clearer that this is something that should be reworked by ZONE_DEVICE people rather sooner than later. Thanks! >=20 > Thanks! >=20 >> Reported-by: Qian Cai >> Cc: Alexey Dobriyan >> Cc: Naoya Horiguchi >> Cc: Andrew Morton >> Cc: Stephen Rothwell >> Cc: Michal Hocko >> Cc: Toshiki Fukasawa >> Cc: David Hildenbrand >> Cc: Konstantin Khlebnikov >> Cc: Mike Rapoport >> Cc: Anthony Yznaga >> Cc: Jason Gunthorpe >> Cc: Dan Williams >> Cc: Logan Gunthorpe >> Cc: Ira Weiny >> Cc: "Aneesh Kumar K.V" >> Cc: linux-fsdevel@vger.kernel.org >> Signed-off-by: David Hildenbrand >> --- >> fs/proc/page.c | 12 ++++++------ >> include/linux/memremap.h | 11 +++++++++-- >> mm/memory-failure.c | 22 ++++++++++++++++------ >> mm/memremap.c | 19 +++++++++++-------- >> 4 files changed, 42 insertions(+), 22 deletions(-) >> >> diff --git a/fs/proc/page.c b/fs/proc/page.c >> index decd3fe39674..76502af461e2 100644 >> --- a/fs/proc/page.c >> +++ b/fs/proc/page.c >> @@ -42,7 +42,8 @@ static ssize_t kpagecount_read(struct file *file, ch= ar __user *buf, >> return -EINVAL; >> =20 >> while (count > 0) { >> - if (pfn_valid(pfn)) >> + if (pfn_valid(pfn) && >> + (pfn_to_online_page(pfn) || pfn_zone_device(pfn))) >> ppage =3D pfn_to_page(pfn); >> else >> ppage =3D NULL; >> @@ -97,9 +98,6 @@ u64 stable_page_flags(struct page *page) >> if (!page) >> return BIT_ULL(KPF_NOPAGE); >> =20 >> - if (pfn_zone_device_reserved(page_to_pfn(page))) >> - return BIT_ULL(KPF_RESERVED); >> - >> k =3D page->flags; >> u =3D 0; >> =20 >> @@ -218,7 +216,8 @@ static ssize_t kpageflags_read(struct file *file, = char __user *buf, >> return -EINVAL; >> =20 >> while (count > 0) { >> - if (pfn_valid(pfn)) >> + if (pfn_valid(pfn) && >> + (pfn_to_online_page(pfn) || pfn_zone_device(pfn))) >> ppage =3D pfn_to_page(pfn); >> else >> ppage =3D NULL; >> @@ -263,7 +262,8 @@ static ssize_t kpagecgroup_read(struct file *file,= char __user *buf, >> return -EINVAL; >> =20 >> while (count > 0) { >> - if (pfn_valid(pfn)) >> + if (pfn_valid(pfn) && >> + (pfn_to_online_page(pfn) || pfn_zone_device(pfn))) >> ppage =3D pfn_to_page(pfn); >> else >> ppage =3D NULL; >> diff --git a/include/linux/memremap.h b/include/linux/memremap.h >> index c676e33205d3..c076bb163c2f 100644 >> --- a/include/linux/memremap.h >> +++ b/include/linux/memremap.h >> @@ -123,7 +123,8 @@ static inline struct vmem_altmap *pgmap_altmap(str= uct dev_pagemap *pgmap) >> } >> =20 >> #ifdef CONFIG_ZONE_DEVICE >> -bool pfn_zone_device_reserved(unsigned long pfn); >> +bool pfn_zone_device(unsigned long pfn); >> +bool __pfn_zone_device(unsigned long pfn, struct dev_pagemap *pgmap); >> void *memremap_pages(struct dev_pagemap *pgmap, int nid); >> void memunmap_pages(struct dev_pagemap *pgmap); >> void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgm= ap); >> @@ -134,7 +135,13 @@ struct dev_pagemap *get_dev_pagemap(unsigned long= pfn, >> unsigned long vmem_altmap_offset(struct vmem_altmap *altmap); >> void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pf= ns); >> #else >> -static inline bool pfn_zone_device_reserved(unsigned long pfn) >> +static inline bool pfn_zone_device(unsigned long pfn) >> +{ >> + return false; >> +} >> + >> +static inline bool __pfn_zone_device(unsigned long pfn, >> + struct dev_pagemap *pgmap) >> { >> return false; >> } >> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >> index 7ef849da8278..2b4cc6b67720 100644 >> --- a/mm/memory-failure.c >> +++ b/mm/memory-failure.c >> @@ -1161,6 +1161,14 @@ static int memory_failure_dev_pagemap(unsigned = long pfn, int flags, >> loff_t start; >> dax_entry_t cookie; >> =20 >> + /* memmaps of driver reserved memory is not initialized */ >> + if (!__pfn_zone_device(pfn, pgmap)) { >> + pr_err("Memory failure: %#lx: driver reserved memory\n", >> + pfn); >> + rc =3D -ENXIO; >> + goto out; >> + } >> + >> /* >> * Prevent the inode from being freed while we are interrogating >> * the address_space, typically this would be handled by >> @@ -1253,17 +1261,19 @@ int memory_failure(unsigned long pfn, int flag= s) >> if (!sysctl_memory_failure_recovery) >> panic("Memory failure on page %lx", pfn); >> =20 >> - if (!pfn_valid(pfn)) { >> + p =3D pfn_to_online_page(pfn); >> + if (!p) { >> + if (pfn_valid(pfn)) { >> + pgmap =3D get_dev_pagemap(pfn, NULL); >> + if (pgmap) >> + return memory_failure_dev_pagemap(pfn, flags, >> + pgmap); >> + } >> pr_err("Memory failure: %#lx: memory outside kernel control\n", >> pfn); >> return -ENXIO; >> } >> =20 >> - pgmap =3D get_dev_pagemap(pfn, NULL); >> - if (pgmap) >> - return memory_failure_dev_pagemap(pfn, flags, pgmap); >> - >> - p =3D pfn_to_page(pfn); >> if (PageHuge(p)) >> return memory_failure_hugetlb(pfn, flags); >> if (TestSetPageHWPoison(p)) { >> diff --git a/mm/memremap.c b/mm/memremap.c >> index 7fed8bd32a18..9f3bb223aec7 100644 >> --- a/mm/memremap.c >> +++ b/mm/memremap.c >> @@ -73,21 +73,24 @@ static unsigned long pfn_next(unsigned long pfn) >> return pfn + 1; >> } >> =20 >> +bool __pfn_zone_device(unsigned long pfn, struct dev_pagemap *pgmap) >> +{ >> + return pfn >=3D pfn_first(pgmap) && pfn <=3D pfn_end(pgmap); >> +} >> + >> /* >> - * This returns true if the page is reserved by ZONE_DEVICE driver. >> + * Returns true if the page was initialized to the ZONE_DEVICE (espec= ially, >> + * is not reserved for driver usage). >> */ >> -bool pfn_zone_device_reserved(unsigned long pfn) >> +bool pfn_zone_device(unsigned long pfn) >> { >> struct dev_pagemap *pgmap; >> - struct vmem_altmap *altmap; >> - bool ret =3D false; >> + bool ret; >> =20 >> pgmap =3D get_dev_pagemap(pfn, NULL); >> if (!pgmap) >> - return ret; >> - altmap =3D pgmap_altmap(pgmap); >> - if (altmap && pfn < (altmap->base_pfn + altmap->reserve)) >> - ret =3D true; >> + return false; >> + ret =3D __pfn_zone_device(pfn, pgmap); >> put_dev_pagemap(pgmap); >> =20 >> return ret; >> --=20 >> 2.21.0 >=20 --=20 Thanks, David / dhildenb