[PATCH 2/2] /proc/kpageflags: do not use uninitialized struct pages
From: Toshiki Fukasawa
Date: Wed Jul 24 2019 - 22:55:57 EST
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@xxxxxxxxxxxxxxx
Signed-off-by: Toshiki Fukasawa <t-fukasawa@xxxxxxxxxxxxx>
---
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);
+
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);
+ 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))
--
1.8.3.1