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SubjectRe: [PATCH v1] mm: Fix access of uninitialized memmaps in fs/proc/page.c
Date
Hi David,

On Wed, Oct 09, 2019 at 11:12:04AM +0200, 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/page.c

Ah right, memory_failure is another victim of this bug.

>
> We have initialized memmaps either when the section is online or when
> the page was initialized to the ZONE_DEVICE. Uninitialized memmaps contain
> 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/kpagecount
> with CONFIG_PAGE_POISONING:
> :/# cat /proc/kpagecount > tmp.test
> [ 95.600592] BUG: unable to handle page fault for address: fffffffffffffffe
> [ 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-20191004+ #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 e7 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: 0000000000000000
> [ 95.607519] RDX: 0000000000000001 RSI: 00007f76b5595000 RDI: fffff35645000000
> [ 95.608128] RBP: 00007f76b5595000 R08: 0000000000000001 R09: 0000000000000000
> [ 95.608731] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000140000
> [ 95.609327] R13: 0000000000020000 R14: 00007f76b5595000 R15: ffffa14e409b7f08
> [ 95.609924] FS: 00007f76b577d580(0000) GS:ffff8f41bd400000(0000) knlGS:0000000000000000
> [ 95.610599] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 95.611083] CR2: fffffffffffffffe CR3: 0000000078960000 CR4: 00000000000006f0
> [ 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 the
> ZONE_DEVICE detection.

Actually, Toshiki is writing code to refactor and optimize the pfn walking
part, where we find the pfn ranges covered by zone devices by running over
xarray pgmap_array and use the range info to reduce pointer dereferences
to speed up pfn walk. I hope he will share it soon.

Thanks,
Naoya Horiguchi

> This patch now also makes sure we don't dump data
> about memory blocks that are already offline again.
>
> Reported-by: Qian Cai <cai@lca.pw>
> Cc: Alexey Dobriyan <adobriyan@gmail.com>
> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Stephen Rothwell <sfr@canb.auug.org.au>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Toshiki Fukasawa <t-fukasawa@vx.jp.nec.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Konstantin Khlebnikov <koct9i@gmail.com>
> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
> Cc: Anthony Yznaga <anthony.yznaga@oracle.com>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Logan Gunthorpe <logang@deltatee.com>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
> Cc: linux-fsdevel@vger.kernel.org
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> 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, char __user *buf,
> return -EINVAL;
>
> while (count > 0) {
> - if (pfn_valid(pfn))
> + if (pfn_valid(pfn) &&
> + (pfn_to_online_page(pfn) || pfn_zone_device(pfn)))
> ppage = pfn_to_page(pfn);
> else
> ppage = NULL;
> @@ -97,9 +98,6 @@ 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;
>
> @@ -218,7 +216,8 @@ static ssize_t kpageflags_read(struct file *file, char __user *buf,
> return -EINVAL;
>
> while (count > 0) {
> - if (pfn_valid(pfn))
> + if (pfn_valid(pfn) &&
> + (pfn_to_online_page(pfn) || pfn_zone_device(pfn)))
> ppage = pfn_to_page(pfn);
> else
> ppage = NULL;
> @@ -263,7 +262,8 @@ static ssize_t kpagecgroup_read(struct file *file, char __user *buf,
> return -EINVAL;
>
> while (count > 0) {
> - if (pfn_valid(pfn))
> + if (pfn_valid(pfn) &&
> + (pfn_to_online_page(pfn) || pfn_zone_device(pfn)))
> ppage = pfn_to_page(pfn);
> else
> ppage = 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(struct dev_pagemap *pgmap)
> }
>
> #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 *pgmap);
> @@ -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_pfns);
> #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;
>
> + /* 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 = -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 flags)
> if (!sysctl_memory_failure_recovery)
> panic("Memory failure on page %lx", pfn);
>
> - if (!pfn_valid(pfn)) {
> + p = pfn_to_online_page(pfn);
> + if (!p) {
> + if (pfn_valid(pfn)) {
> + pgmap = 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;
> }
>
> - pgmap = get_dev_pagemap(pfn, NULL);
> - if (pgmap)
> - return memory_failure_dev_pagemap(pfn, flags, pgmap);
> -
> - p = 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;
> }
>
> +bool __pfn_zone_device(unsigned long pfn, struct dev_pagemap *pgmap)
> +{
> + return pfn >= pfn_first(pgmap) && pfn <= 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 (especially,
> + * 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 = false;
> + bool ret;
>
> pgmap = get_dev_pagemap(pfn, NULL);
> if (!pgmap)
> - return ret;
> - altmap = pgmap_altmap(pgmap);
> - if (altmap && pfn < (altmap->base_pfn + altmap->reserve))
> - ret = true;
> + return false;
> + ret = __pfn_zone_device(pfn, pgmap);
> put_dev_pagemap(pgmap);
>
> return ret;
> --
> 2.21.0
>
>

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