[PATCH v2 2/3] fs/proc/page.c: allow inspection of last section and fix end detection

David Hildenbrand
2019-12-11T16:32:25Z

If max_pfn does not fall onto a section boundary, it is possible to inspect
PFNs up to max_pfn, and PFNs above max_pfn, however, max_pfn itself can't
be inspected. We can have a valid (and online) memmap at and above max_pfn
if max_pfn is not aligned to a section boundary. The whole early section
has a memmap and is marked online. Being able to inspect the state of these
PFNs is valuable for debugging, especially because max_pfn can change on
memory hotplug and expose these memmaps.

Also, querying page flags via "./page-types -r -a 0x144001,"
(tools/vm/page-types.c) inside a x86-64 guest with 4160MB under QEMU
results in an (almost) endless loop in user space, because the end is
not detected properly when starting after max_pfn.

Instead, let's allow to inspect all pages in the highest section and
return 0 directly if we try to access pages above that section.

While at it, check the count before adjusting it, to avoid masking user
errors.

Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: David Hildenbrand <david@redhat.com>
---
fs/proc/page.c | 30 +++++++++++++++++++++++++++---
1 file changed, 27 insertions(+), 3 deletions(-)

diff --git a/fs/proc/page.c b/fs/proc/page.c
index e40dbfe1168e..2984df28ccea 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -21,6 +21,21 @@
#define KPMMASK (KPMSIZE - 1)
#define KPMBITS (KPMSIZE * BITS_PER_BYTE)

+static inline unsigned long get_max_dump_pfn(void)
+{
+#ifdef CONFIG_SPARSEMEM
+ /*
+ * The memmap of early sections is completely populated and marked
+ * online even if max_pfn does not fall on a section boundary -
+ * pfn_to_online_page() will succeed on all pages. Allow inspecting
+ * these memmaps.
+ */
+ return round_up(max_pfn, PAGES_PER_SECTION);
+#else
+ return max_pfn;
+#endif
+}
+
/* /proc/kpagecount - an array exposing page counts
*
* Each entry is a u64 representing the corresponding
@@ -29,6 +44,7 @@
static ssize_t kpagecount_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
+ const unsigned long max_dump_pfn = get_max_dump_pfn();
u64 __user *out = (u64 __user *)buf;
struct page *ppage;
unsigned long src = *ppos;
@@ -37,9 +53,11 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf,
u64 pcount;

pfn = src / KPMSIZE;
- count = min_t(size_t, count, (max_pfn * KPMSIZE) - src);
if (src & KPMMASK || count & KPMMASK)
return -EINVAL;
+ if (src >= max_dump_pfn * KPMSIZE)
+ return 0;
+ count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);

while (count > 0) {
/*
@@ -208,6 +226,7 @@ u64 stable_page_flags(struct page *page)
static ssize_t kpageflags_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
+ const unsigned long max_dump_pfn = get_max_dump_pfn();
u64 __user *out = (u64 __user *)buf;
struct page *ppage;
unsigned long src = *ppos;
@@ -215,9 +234,11 @@ static ssize_t kpageflags_read(struct file *file, char __user *buf,
ssize_t ret = 0;

pfn = src / KPMSIZE;
- count = min_t(unsigned long, count, (max_pfn * KPMSIZE) - src);
if (src & KPMMASK || count & KPMMASK)
return -EINVAL;
+ if (src >= max_dump_pfn * KPMSIZE)
+ return 0;
+ count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);

while (count > 0) {
/*
@@ -253,6 +274,7 @@ static const struct file_operations proc_kpageflags_operations = {
static ssize_t kpagecgroup_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
+ const unsigned long max_dump_pfn = get_max_dump_pfn();
u64 __user *out = (u64 __user *)buf;
struct page *ppage;
unsigned long src = *ppos;
@@ -261,9 +283,11 @@ static ssize_t kpagecgroup_read(struct file *file, char __user *buf,
u64 ino;

pfn = src / KPMSIZE;
- count = min_t(unsigned long, count, (max_pfn * KPMSIZE) - src);
if (src & KPMMASK || count & KPMMASK)
return -EINVAL;
+ if (src >= max_dump_pfn * KPMSIZE)
+ return 0;
+ count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);

while (count > 0) {
/*
--
2.23.0