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Date: Mon, 5 Aug 2019 20:34:27 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Toshiki Fukasawa <t-fukasawa@...jp.nec.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"mhocko@...nel.org" <mhocko@...nel.org>,
"adobriyan@...il.com" <adobriyan@...il.com>,
"hch@....de" <hch@....de>,
Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
Junichi Nomura <j-nomura@...jp.nec.com>,
"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 2/2] /proc/kpageflags: do not use uninitialized struct pages
On Wed, Jul 24, 2019 at 7:46 PM Toshiki Fukasawa
<t-fukasawa@...jp.nec.com> wrote:
>
> 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.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: Toshiki Fukasawa <t-fukasawa@...jp.nec.com>
> ---
> fs/proc/page.c | 3 +++
> include/linux/memremap.h | 6 ++++++
> kernel/memremap.c | 20 ++++++++++++++++++++
> 3 files changed, 29 insertions(+)
>
> diff --git a/fs/proc/page.c b/fs/proc/page.c
> index 69064ad..decd3fe 100644
> --- a/fs/proc/page.c
> +++ b/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);
I think this should be KPF_NOPAGE. KPF_RESERVED implies a page is present.
> +
> k = page->flags;
> u = 0;
>
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index f8a5b2a..2cfc3c2 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -124,6 +124,7 @@ static inline struct vmem_altmap *pgmap_altmap(struct dev_pagemap *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(unsigned long pfn,
> 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)
> {
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index 6ee03a8..bc3471c 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -72,6 +72,26 @@ static unsigned long pfn_next(unsigned long pfn)
> 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);
Ugh this will drastically slow down kpageflags_read() for all other
pfn ranges. What about burning another section flag to indicate
'device' sections so that we have a quick lookup for
pfn_is_zone_device()?
> + if (!pgmap)
> + return ret;
If pfn_is_zone_device() returns true than a failure to retrieve the
dev_pagemap should result in this routine returning true as well
because it means the driver hosting the device is in the process of
tearing down the mapping.
> + 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))
>
> --
> 1.8.3.1
>
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