[PATCH 0/7] /proc/kcore improvements

[PATCH 0/7] /proc/kcore improvements

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

Hi,

This series makes a few improvements to /proc/kcore. Patches 1 and 2 are
prep patches. Patch 3 is a fix/cleanup. Patch 4 is another prep patch.
Patches 5 and 6 are optimizations to ->read(). Patch 7 adds vmcoreinfo
to /proc/kcore. This series is based on v4.18-rc3. Please consider it
for v4.19.

Thanks!

Omar Sandoval (7):
  proc/kcore: don't grab lock for kclist_add()
  proc/kcore: replace kclist_lock rwlock with rwsem
  proc/kcore: fix memory hotplug vs multiple opens race
  proc/kcore: hold lock during read
  proc/kcore: clean up ELF header generation
  proc/kcore: optimize multiple page reads
  proc/kcore: add vmcoreinfo note to /proc/kcore

 fs/proc/Kconfig            |   1 +
 fs/proc/kcore.c            | 524 +++++++++++++++++--------------------
 include/linux/crash_core.h |   2 +
 kernel/crash_core.c        |   4 +-
 4 files changed, 241 insertions(+), 290 deletions(-)

-- 
2.18.0

[PATCH 1/7] proc/kcore: don't grab lock for kclist_add()

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

kclist_add() is only called at init time, so there's no point in
grabbing any locks. We're also going to replace the rwlock with a rwsem,
which we don't want to try grabbing during early boot.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 fs/proc/kcore.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index e64ecb9f2720..afd1ff8c2d3f 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -62,6 +62,7 @@ static LIST_HEAD(kclist_head);
 static DEFINE_RWLOCK(kclist_lock);
 static int kcore_need_update = 1;
 
+/* This doesn't grab kclist_lock, so it should only be used at init time. */
 void
 kclist_add(struct kcore_list *new, void *addr, size_t size, int type)
 {
@@ -69,9 +70,7 @@ kclist_add(struct kcore_list *new, void *addr, size_t size, int type)
 	new->size = size;
 	new->type = type;
 
-	write_lock(&kclist_lock);
 	list_add_tail(&new->list, &kclist_head);
-	write_unlock(&kclist_lock);
 }
 
 static size_t get_kcore_size(int *nphdr, size_t *elf_buflen)
-- 
2.18.0

[PATCH 2/7] proc/kcore: replace kclist_lock rwlock with rwsem

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

Now we only need kclist_lock from user context and at fs init time, and
the following changes need to sleep while holding the kclist_lock.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 fs/proc/kcore.c | 32 +++++++++++++++-----------------
 1 file changed, 15 insertions(+), 17 deletions(-)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index afd1ff8c2d3f..eb1be07bdb3d 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -59,8 +59,8 @@ struct memelfnote
 };
 
 static LIST_HEAD(kclist_head);
-static DEFINE_RWLOCK(kclist_lock);
-static int kcore_need_update = 1;
+static DECLARE_RWSEM(kclist_lock);
+static atomic_t kcore_need_update = ATOMIC_INIT(1);
 
 /* This doesn't grab kclist_lock, so it should only be used at init time. */
 void
@@ -117,8 +117,8 @@ static void __kcore_update_ram(struct list_head *list)
 	struct kcore_list *tmp, *pos;
 	LIST_HEAD(garbage);
 
-	write_lock(&kclist_lock);
-	if (kcore_need_update) {
+	down_write(&kclist_lock);
+	if (atomic_cmpxchg(&kcore_need_update, 1, 0)) {
 		list_for_each_entry_safe(pos, tmp, &kclist_head, list) {
 			if (pos->type == KCORE_RAM
 				|| pos->type == KCORE_VMEMMAP)
@@ -127,9 +127,8 @@ static void __kcore_update_ram(struct list_head *list)
 		list_splice_tail(list, &kclist_head);
 	} else
 		list_splice(list, &garbage);
-	kcore_need_update = 0;
 	proc_root_kcore->size = get_kcore_size(&nphdr, &size);
-	write_unlock(&kclist_lock);
+	up_write(&kclist_lock);
 
 	free_kclist_ents(&garbage);
 }
@@ -450,11 +449,11 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 	int nphdr;
 	unsigned long start;
 
-	read_lock(&kclist_lock);
+	down_read(&kclist_lock);
 	size = get_kcore_size(&nphdr, &elf_buflen);
 
 	if (buflen == 0 || *fpos >= size) {
-		read_unlock(&kclist_lock);
+		up_read(&kclist_lock);
 		return 0;
 	}
 
@@ -471,11 +470,11 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 			tsz = buflen;
 		elf_buf = kzalloc(elf_buflen, GFP_ATOMIC);
 		if (!elf_buf) {
-			read_unlock(&kclist_lock);
+			up_read(&kclist_lock);
 			return -ENOMEM;
 		}
 		elf_kcore_store_hdr(elf_buf, nphdr, elf_buflen);
-		read_unlock(&kclist_lock);
+		up_read(&kclist_lock);
 		if (copy_to_user(buffer, elf_buf + *fpos, tsz)) {
 			kfree(elf_buf);
 			return -EFAULT;
@@ -490,7 +489,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 		if (buflen == 0)
 			return acc;
 	} else
-		read_unlock(&kclist_lock);
+		up_read(&kclist_lock);
 
 	/*
 	 * Check to see if our file offset matches with any of
@@ -503,12 +502,12 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 	while (buflen) {
 		struct kcore_list *m;
 
-		read_lock(&kclist_lock);
+		down_read(&kclist_lock);
 		list_for_each_entry(m, &kclist_head, list) {
 			if (start >= m->addr && start < (m->addr+m->size))
 				break;
 		}
-		read_unlock(&kclist_lock);
+		up_read(&kclist_lock);
 
 		if (&m->list == &kclist_head) {
 			if (clear_user(buffer, tsz))
@@ -561,7 +560,7 @@ static int open_kcore(struct inode *inode, struct file *filp)
 	if (!filp->private_data)
 		return -ENOMEM;
 
-	if (kcore_need_update)
+	if (atomic_read(&kcore_need_update))
 		kcore_update_ram();
 	if (i_size_read(inode) != proc_root_kcore->size) {
 		inode_lock(inode);
@@ -591,9 +590,8 @@ static int __meminit kcore_callback(struct notifier_block *self,
 	switch (action) {
 	case MEM_ONLINE:
 	case MEM_OFFLINE:
-		write_lock(&kclist_lock);
-		kcore_need_update = 1;
-		write_unlock(&kclist_lock);
+		atomic_set(&kcore_need_update, 1);
+		break;
 	}
 	return NOTIFY_OK;
 }
-- 
2.18.0

[PATCH 3/7] proc/kcore: fix memory hotplug vs multiple opens race

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

There's a theoretical race condition that will cause /proc/kcore to miss
a memory hotplug event:

CPU0                              CPU1
// hotplug event 1
kcore_need_update = 1

open_kcore()                      open_kcore()
    kcore_update_ram()                kcore_update_ram()
        // Walk RAM                       // Walk RAM
        __kcore_update_ram()              __kcore_update_ram()
            kcore_need_update = 0

// hotplug event 2
kcore_need_update = 1
                                              kcore_need_update = 0

Note that CPU1 set up the RAM kcore entries with the state after hotplug
event 1 but cleared the flag for hotplug event 2. The RAM entries will
therefore be stale until there is another hotplug event.

This is an extremely unlikely sequence of events, but the fix makes the
synchronization saner, anyways: we serialize the entire update sequence,
which means that whoever clears the flag will always succeed in
replacing the kcore list.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 fs/proc/kcore.c | 93 +++++++++++++++++++++++--------------------------
 1 file changed, 44 insertions(+), 49 deletions(-)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index eb1be07bdb3d..f335400300d3 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -98,53 +98,15 @@ static size_t get_kcore_size(int *nphdr, size_t *elf_buflen)
 	return size + *elf_buflen;
 }
 
-static void free_kclist_ents(struct list_head *head)
-{
-	struct kcore_list *tmp, *pos;
-
-	list_for_each_entry_safe(pos, tmp, head, list) {
-		list_del(&pos->list);
-		kfree(pos);
-	}
-}
-/*
- * Replace all KCORE_RAM/KCORE_VMEMMAP information with passed list.
- */
-static void __kcore_update_ram(struct list_head *list)
-{
-	int nphdr;
-	size_t size;
-	struct kcore_list *tmp, *pos;
-	LIST_HEAD(garbage);
-
-	down_write(&kclist_lock);
-	if (atomic_cmpxchg(&kcore_need_update, 1, 0)) {
-		list_for_each_entry_safe(pos, tmp, &kclist_head, list) {
-			if (pos->type == KCORE_RAM
-				|| pos->type == KCORE_VMEMMAP)
-				list_move(&pos->list, &garbage);
-		}
-		list_splice_tail(list, &kclist_head);
-	} else
-		list_splice(list, &garbage);
-	proc_root_kcore->size = get_kcore_size(&nphdr, &size);
-	up_write(&kclist_lock);
-
-	free_kclist_ents(&garbage);
-}
-
-
 #ifdef CONFIG_HIGHMEM
 /*
  * If no highmem, we can assume [0...max_low_pfn) continuous range of memory
  * because memory hole is not as big as !HIGHMEM case.
  * (HIGHMEM is special because part of memory is _invisible_ from the kernel.)
  */
-static int kcore_update_ram(void)
+static int kcore_ram_list(struct list_head *head)
 {
-	LIST_HEAD(head);
 	struct kcore_list *ent;
-	int ret = 0;
 
 	ent = kmalloc(sizeof(*ent), GFP_KERNEL);
 	if (!ent)
@@ -152,9 +114,8 @@ static int kcore_update_ram(void)
 	ent->addr = (unsigned long)__va(0);
 	ent->size = max_low_pfn << PAGE_SHIFT;
 	ent->type = KCORE_RAM;
-	list_add(&ent->list, &head);
-	__kcore_update_ram(&head);
-	return ret;
+	list_add(&ent->list, head);
+	return 0;
 }
 
 #else /* !CONFIG_HIGHMEM */
@@ -253,11 +214,10 @@ kclist_add_private(unsigned long pfn, unsigned long nr_pages, void *arg)
 	return 1;
 }
 
-static int kcore_update_ram(void)
+static int kcore_ram_list(struct list_head *list)
 {
 	int nid, ret;
 	unsigned long end_pfn;
-	LIST_HEAD(head);
 
 	/* Not inialized....update now */
 	/* find out "max pfn" */
@@ -269,15 +229,50 @@ static int kcore_update_ram(void)
 			end_pfn = node_end;
 	}
 	/* scan 0 to max_pfn */
-	ret = walk_system_ram_range(0, end_pfn, &head, kclist_add_private);
-	if (ret) {
-		free_kclist_ents(&head);
+	ret = walk_system_ram_range(0, end_pfn, list, kclist_add_private);
+	if (ret)
 		return -ENOMEM;
+	return 0;
+}
+#endif /* CONFIG_HIGHMEM */
+
+static int kcore_update_ram(void)
+{
+	LIST_HEAD(list);
+	LIST_HEAD(garbage);
+	int nphdr;
+	size_t size;
+	struct kcore_list *tmp, *pos;
+	int ret = 0;
+
+	down_write(&kclist_lock);
+	if (!atomic_cmpxchg(&kcore_need_update, 1, 0))
+		goto out;
+
+	ret = kcore_ram_list(&list);
+	if (ret) {
+		/* Couldn't get the RAM list, try again next time. */
+		atomic_set(&kcore_need_update, 1);
+		list_splice_tail(&list, &garbage);
+		goto out;
+	}
+
+	list_for_each_entry_safe(pos, tmp, &kclist_head, list) {
+		if (pos->type == KCORE_RAM || pos->type == KCORE_VMEMMAP)
+			list_move(&pos->list, &garbage);
+	}
+	list_splice_tail(&list, &kclist_head);
+
+	proc_root_kcore->size = get_kcore_size(&nphdr, &size);
+
+out:
+	up_write(&kclist_lock);
+	list_for_each_entry_safe(pos, tmp, &garbage, list) {
+		list_del(&pos->list);
+		kfree(pos);
 	}
-	__kcore_update_ram(&head);
 	return ret;
 }
-#endif /* CONFIG_HIGHMEM */
 
 /*****************************************************************************/
 /*
-- 
2.18.0

[PATCH 4/7] proc/kcore: hold lock during read

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

Now that we're using an rwsem, we can hold it during the entirety of
read_kcore() and have a common return path. This is preparation for the
next change.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 fs/proc/kcore.c | 70 ++++++++++++++++++++++++++++---------------------
 1 file changed, 40 insertions(+), 30 deletions(-)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index f335400300d3..b7ff2e2ec350 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -438,19 +438,18 @@ static ssize_t
 read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 {
 	char *buf = file->private_data;
-	ssize_t acc = 0;
 	size_t size, tsz;
 	size_t elf_buflen;
 	int nphdr;
 	unsigned long start;
+	size_t orig_buflen = buflen;
+	int ret = 0;
 
 	down_read(&kclist_lock);
 	size = get_kcore_size(&nphdr, &elf_buflen);
 
-	if (buflen == 0 || *fpos >= size) {
-		up_read(&kclist_lock);
-		return 0;
-	}
+	if (buflen == 0 || *fpos >= size)
+		goto out;
 
 	/* trim buflen to not go beyond EOF */
 	if (buflen > size - *fpos)
@@ -463,28 +462,26 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 		tsz = elf_buflen - *fpos;
 		if (buflen < tsz)
 			tsz = buflen;
-		elf_buf = kzalloc(elf_buflen, GFP_ATOMIC);
+		elf_buf = kzalloc(elf_buflen, GFP_KERNEL);
 		if (!elf_buf) {
-			up_read(&kclist_lock);
-			return -ENOMEM;
+			ret = -ENOMEM;
+			goto out;
 		}
 		elf_kcore_store_hdr(elf_buf, nphdr, elf_buflen);
-		up_read(&kclist_lock);
 		if (copy_to_user(buffer, elf_buf + *fpos, tsz)) {
 			kfree(elf_buf);
-			return -EFAULT;
+			ret = -EFAULT;
+			goto out;
 		}
 		kfree(elf_buf);
 		buflen -= tsz;
 		*fpos += tsz;
 		buffer += tsz;
-		acc += tsz;
 
 		/* leave now if filled buffer already */
 		if (buflen == 0)
-			return acc;
-	} else
-		up_read(&kclist_lock);
+			goto out;
+	}
 
 	/*
 	 * Check to see if our file offset matches with any of
@@ -497,25 +494,29 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 	while (buflen) {
 		struct kcore_list *m;
 
-		down_read(&kclist_lock);
 		list_for_each_entry(m, &kclist_head, list) {
 			if (start >= m->addr && start < (m->addr+m->size))
 				break;
 		}
-		up_read(&kclist_lock);
 
 		if (&m->list == &kclist_head) {
-			if (clear_user(buffer, tsz))
-				return -EFAULT;
+			if (clear_user(buffer, tsz)) {
+				ret = -EFAULT;
+				goto out;
+			}
 		} else if (m->type == KCORE_VMALLOC) {
 			vread(buf, (char *)start, tsz);
 			/* we have to zero-fill user buffer even if no read */
-			if (copy_to_user(buffer, buf, tsz))
-				return -EFAULT;
+			if (copy_to_user(buffer, buf, tsz)) {
+				ret = -EFAULT;
+				goto out;
+			}
 		} else if (m->type == KCORE_USER) {
 			/* User page is handled prior to normal kernel page: */
-			if (copy_to_user(buffer, (char *)start, tsz))
-				return -EFAULT;
+			if (copy_to_user(buffer, (char *)start, tsz)) {
+				ret = -EFAULT;
+				goto out;
+			}
 		} else {
 			if (kern_addr_valid(start)) {
 				/*
@@ -523,26 +524,35 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 				 * hardened user copy kernel text checks.
 				 */
 				if (probe_kernel_read(buf, (void *) start, tsz)) {
-					if (clear_user(buffer, tsz))
-						return -EFAULT;
+					if (clear_user(buffer, tsz)) {
+						ret = -EFAULT;
+						goto out;
+					}
 				} else {
-					if (copy_to_user(buffer, buf, tsz))
-						return -EFAULT;
+					if (copy_to_user(buffer, buf, tsz)) {
+						ret = -EFAULT;
+						goto out;
+					}
 				}
 			} else {
-				if (clear_user(buffer, tsz))
-					return -EFAULT;
+				if (clear_user(buffer, tsz)) {
+					ret = -EFAULT;
+					goto out;
+				}
 			}
 		}
 		buflen -= tsz;
 		*fpos += tsz;
 		buffer += tsz;
-		acc += tsz;
 		start += tsz;
 		tsz = (buflen > PAGE_SIZE ? PAGE_SIZE : buflen);
 	}
 
-	return acc;
+out:
+	up_write(&kclist_lock);
+	if (ret)
+		return ret;
+	return orig_buflen - buflen;
 }
 
 
-- 
2.18.0

[PATCH 5/7] proc/kcore: clean up ELF header generation

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

Currently, the ELF file header, program headers, and note segment are
allocated all at once, in some icky code dating back to 2.3. Programs
tend to read the file header, then the program headers, then the note
segment, all separately, so this is a waste of effort. It's cleaner and
more efficient to handle the three separately.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 fs/proc/kcore.c | 346 +++++++++++++++++++-----------------------------
 1 file changed, 139 insertions(+), 207 deletions(-)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index b7ff2e2ec350..de225b61f34f 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -49,15 +49,6 @@ static struct proc_dir_entry *proc_root_kcore;
 #define	kc_offset_to_vaddr(o) ((o) + PAGE_OFFSET)
 #endif
 
-/* An ELF note in memory */
-struct memelfnote
-{
-	const char *name;
-	int type;
-	unsigned int datasz;
-	void *data;
-};
-
 static LIST_HEAD(kclist_head);
 static DECLARE_RWSEM(kclist_lock);
 static atomic_t kcore_need_update = ATOMIC_INIT(1);
@@ -73,7 +64,8 @@ kclist_add(struct kcore_list *new, void *addr, size_t size, int type)
 	list_add_tail(&new->list, &kclist_head);
 }
 
-static size_t get_kcore_size(int *nphdr, size_t *elf_buflen)
+static size_t get_kcore_size(int *nphdr, size_t *phdrs_len, size_t *notes_len,
+			     size_t *data_offset)
 {
 	size_t try, size;
 	struct kcore_list *m;
@@ -87,15 +79,15 @@ static size_t get_kcore_size(int *nphdr, size_t *elf_buflen)
 			size = try;
 		*nphdr = *nphdr + 1;
 	}
-	*elf_buflen =	sizeof(struct elfhdr) + 
-			(*nphdr + 2)*sizeof(struct elf_phdr) + 
-			3 * ((sizeof(struct elf_note)) +
-			     roundup(sizeof(CORE_STR), 4)) +
-			roundup(sizeof(struct elf_prstatus), 4) +
-			roundup(sizeof(struct elf_prpsinfo), 4) +
-			roundup(arch_task_struct_size, 4);
-	*elf_buflen = PAGE_ALIGN(*elf_buflen);
-	return size + *elf_buflen;
+
+	*phdrs_len = *nphdr * sizeof(struct elf_phdr);
+	*notes_len = (3 * (sizeof(struct elf_note) + ALIGN(sizeof(CORE_STR), 4)) +
+		      ALIGN(sizeof(struct elf_prstatus), 4) +
+		      ALIGN(sizeof(struct elf_prpsinfo), 4) +
+		      ALIGN(arch_task_struct_size, 4));
+	*data_offset = PAGE_ALIGN(sizeof(struct elfhdr) + *phdrs_len +
+				  *notes_len);
+	return *data_offset + size;
 }
 
 #ifdef CONFIG_HIGHMEM
@@ -241,7 +233,7 @@ static int kcore_update_ram(void)
 	LIST_HEAD(list);
 	LIST_HEAD(garbage);
 	int nphdr;
-	size_t size;
+	size_t phdrs_len, notes_len, data_offset;
 	struct kcore_list *tmp, *pos;
 	int ret = 0;
 
@@ -263,7 +255,8 @@ static int kcore_update_ram(void)
 	}
 	list_splice_tail(&list, &kclist_head);
 
-	proc_root_kcore->size = get_kcore_size(&nphdr, &size);
+	proc_root_kcore->size = get_kcore_size(&nphdr, &phdrs_len, &notes_len,
+					       &data_offset);
 
 out:
 	up_write(&kclist_lock);
@@ -274,226 +267,166 @@ static int kcore_update_ram(void)
 	return ret;
 }
 
-/*****************************************************************************/
-/*
- * determine size of ELF note
- */
-static int notesize(struct memelfnote *en)
+static void append_kcore_note(char *notes, size_t *i, const char *name,
+			      unsigned int type, const void *desc,
+			      size_t descsz)
 {
-	int sz;
-
-	sz = sizeof(struct elf_note);
-	sz += roundup((strlen(en->name) + 1), 4);
-	sz += roundup(en->datasz, 4);
-
-	return sz;
-} /* end notesize() */
-
-/*****************************************************************************/
-/*
- * store a note in the header buffer
- */
-static char *storenote(struct memelfnote *men, char *bufp)
-{
-	struct elf_note en;
-
-#define DUMP_WRITE(addr,nr) do { memcpy(bufp,addr,nr); bufp += nr; } while(0)
-
-	en.n_namesz = strlen(men->name) + 1;
-	en.n_descsz = men->datasz;
-	en.n_type = men->type;
-
-	DUMP_WRITE(&en, sizeof(en));
-	DUMP_WRITE(men->name, en.n_namesz);
-
-	/* XXX - cast from long long to long to avoid need for libgcc.a */
-	bufp = (char*) roundup((unsigned long)bufp,4);
-	DUMP_WRITE(men->data, men->datasz);
-	bufp = (char*) roundup((unsigned long)bufp,4);
-
-#undef DUMP_WRITE
-
-	return bufp;
-} /* end storenote() */
-
-/*
- * store an ELF coredump header in the supplied buffer
- * nphdr is the number of elf_phdr to insert
- */
-static void elf_kcore_store_hdr(char *bufp, int nphdr, int dataoff)
-{
-	struct elf_prstatus prstatus;	/* NT_PRSTATUS */
-	struct elf_prpsinfo prpsinfo;	/* NT_PRPSINFO */
-	struct elf_phdr *nhdr, *phdr;
-	struct elfhdr *elf;
-	struct memelfnote notes[3];
-	off_t offset = 0;
-	struct kcore_list *m;
-
-	/* setup ELF header */
-	elf = (struct elfhdr *) bufp;
-	bufp += sizeof(struct elfhdr);
-	offset += sizeof(struct elfhdr);
-	memcpy(elf->e_ident, ELFMAG, SELFMAG);
-	elf->e_ident[EI_CLASS]	= ELF_CLASS;
-	elf->e_ident[EI_DATA]	= ELF_DATA;
-	elf->e_ident[EI_VERSION]= EV_CURRENT;
-	elf->e_ident[EI_OSABI] = ELF_OSABI;
-	memset(elf->e_ident+EI_PAD, 0, EI_NIDENT-EI_PAD);
-	elf->e_type	= ET_CORE;
-	elf->e_machine	= ELF_ARCH;
-	elf->e_version	= EV_CURRENT;
-	elf->e_entry	= 0;
-	elf->e_phoff	= sizeof(struct elfhdr);
-	elf->e_shoff	= 0;
-	elf->e_flags	= ELF_CORE_EFLAGS;
-	elf->e_ehsize	= sizeof(struct elfhdr);
-	elf->e_phentsize= sizeof(struct elf_phdr);
-	elf->e_phnum	= nphdr;
-	elf->e_shentsize= 0;
-	elf->e_shnum	= 0;
-	elf->e_shstrndx	= 0;
-
-	/* setup ELF PT_NOTE program header */
-	nhdr = (struct elf_phdr *) bufp;
-	bufp += sizeof(struct elf_phdr);
-	offset += sizeof(struct elf_phdr);
-	nhdr->p_type	= PT_NOTE;
-	nhdr->p_offset	= 0;
-	nhdr->p_vaddr	= 0;
-	nhdr->p_paddr	= 0;
-	nhdr->p_filesz	= 0;
-	nhdr->p_memsz	= 0;
-	nhdr->p_flags	= 0;
-	nhdr->p_align	= 0;
-
-	/* setup ELF PT_LOAD program header for every area */
-	list_for_each_entry(m, &kclist_head, list) {
-		phdr = (struct elf_phdr *) bufp;
-		bufp += sizeof(struct elf_phdr);
-		offset += sizeof(struct elf_phdr);
-
-		phdr->p_type	= PT_LOAD;
-		phdr->p_flags	= PF_R|PF_W|PF_X;
-		phdr->p_offset	= kc_vaddr_to_offset(m->addr) + dataoff;
-		phdr->p_vaddr	= (size_t)m->addr;
-		if (m->type == KCORE_RAM || m->type == KCORE_TEXT)
-			phdr->p_paddr	= __pa(m->addr);
-		else
-			phdr->p_paddr	= (elf_addr_t)-1;
-		phdr->p_filesz	= phdr->p_memsz	= m->size;
-		phdr->p_align	= PAGE_SIZE;
-	}
-
-	/*
-	 * Set up the notes in similar form to SVR4 core dumps made
-	 * with info from their /proc.
-	 */
-	nhdr->p_offset	= offset;
-
-	/* set up the process status */
-	notes[0].name = CORE_STR;
-	notes[0].type = NT_PRSTATUS;
-	notes[0].datasz = sizeof(struct elf_prstatus);
-	notes[0].data = &prstatus;
-
-	memset(&prstatus, 0, sizeof(struct elf_prstatus));
-
-	nhdr->p_filesz	= notesize(&notes[0]);
-	bufp = storenote(&notes[0], bufp);
-
-	/* set up the process info */
-	notes[1].name	= CORE_STR;
-	notes[1].type	= NT_PRPSINFO;
-	notes[1].datasz	= sizeof(struct elf_prpsinfo);
-	notes[1].data	= &prpsinfo;
-
-	memset(&prpsinfo, 0, sizeof(struct elf_prpsinfo));
-	prpsinfo.pr_state	= 0;
-	prpsinfo.pr_sname	= 'R';
-	prpsinfo.pr_zomb	= 0;
-
-	strcpy(prpsinfo.pr_fname, "vmlinux");
-	strlcpy(prpsinfo.pr_psargs, saved_command_line, sizeof(prpsinfo.pr_psargs));
-
-	nhdr->p_filesz	+= notesize(&notes[1]);
-	bufp = storenote(&notes[1], bufp);
-
-	/* set up the task structure */
-	notes[2].name	= CORE_STR;
-	notes[2].type	= NT_TASKSTRUCT;
-	notes[2].datasz	= arch_task_struct_size;
-	notes[2].data	= current;
-
-	nhdr->p_filesz	+= notesize(&notes[2]);
-	bufp = storenote(&notes[2], bufp);
-
-} /* end elf_kcore_store_hdr() */
+	struct elf_note *note = (struct elf_note *)&notes[*i];
+
+	note->n_namesz = strlen(name) + 1;
+	note->n_descsz = descsz;
+	note->n_type = type;
+	*i += sizeof(*note);
+	memcpy(&notes[*i], name, note->n_namesz);
+	*i = ALIGN(*i + note->n_namesz, 4);
+	memcpy(&notes[*i], desc, descsz);
+	*i = ALIGN(*i + descsz, 4);
+}
 
-/*****************************************************************************/
-/*
- * read from the ELF header and then kernel memory
- */
 static ssize_t
 read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 {
 	char *buf = file->private_data;
-	size_t size, tsz;
-	size_t elf_buflen;
+	size_t phdrs_offset, notes_offset, data_offset;
+	size_t phdrs_len, notes_len;
+	struct kcore_list *m;
+	size_t tsz;
 	int nphdr;
 	unsigned long start;
 	size_t orig_buflen = buflen;
 	int ret = 0;
 
 	down_read(&kclist_lock);
-	size = get_kcore_size(&nphdr, &elf_buflen);
 
-	if (buflen == 0 || *fpos >= size)
-		goto out;
+	get_kcore_size(&nphdr, &phdrs_len, &notes_len, &data_offset);
+	phdrs_offset = sizeof(struct elfhdr);
+	notes_offset = phdrs_offset + phdrs_len;
+
+	/* ELF file header. */
+	if (buflen && *fpos < sizeof(struct elfhdr)) {
+		struct elfhdr ehdr = {
+			.e_ident = {
+				[EI_MAG0] = ELFMAG0,
+				[EI_MAG1] = ELFMAG1,
+				[EI_MAG2] = ELFMAG2,
+				[EI_MAG3] = ELFMAG3,
+				[EI_CLASS] = ELF_CLASS,
+				[EI_DATA] = ELF_DATA,
+				[EI_VERSION] = EV_CURRENT,
+				[EI_OSABI] = ELF_OSABI,
+			},
+			.e_type = ET_CORE,
+			.e_machine = ELF_ARCH,
+			.e_version = EV_CURRENT,
+			.e_phoff = sizeof(struct elfhdr),
+			.e_flags = ELF_CORE_EFLAGS,
+			.e_ehsize = sizeof(struct elfhdr),
+			.e_phentsize = sizeof(struct elf_phdr),
+			.e_phnum = nphdr,
+		};
+
+		tsz = min_t(size_t, buflen, sizeof(struct elfhdr) - *fpos);
+		if (copy_to_user(buffer, (char *)&ehdr + *fpos, tsz)) {
+			ret = -EFAULT;
+			goto out;
+		}
 
-	/* trim buflen to not go beyond EOF */
-	if (buflen > size - *fpos)
-		buflen = size - *fpos;
+		buffer += tsz;
+		buflen -= tsz;
+		*fpos += tsz;
+	}
 
-	/* construct an ELF core header if we'll need some of it */
-	if (*fpos < elf_buflen) {
-		char * elf_buf;
+	/* ELF program headers. */
+	if (buflen && *fpos < phdrs_offset + phdrs_len) {
+		struct elf_phdr *phdrs, *phdr;
 
-		tsz = elf_buflen - *fpos;
-		if (buflen < tsz)
-			tsz = buflen;
-		elf_buf = kzalloc(elf_buflen, GFP_KERNEL);
-		if (!elf_buf) {
+		phdrs = kzalloc(phdrs_len, GFP_KERNEL);
+		if (!phdrs) {
 			ret = -ENOMEM;
 			goto out;
 		}
-		elf_kcore_store_hdr(elf_buf, nphdr, elf_buflen);
-		if (copy_to_user(buffer, elf_buf + *fpos, tsz)) {
-			kfree(elf_buf);
+
+		phdrs[0].p_type = PT_NOTE;
+		phdrs[0].p_offset = notes_offset;
+		phdrs[0].p_filesz = notes_len;
+
+		phdr = &phdrs[1];
+		list_for_each_entry(m, &kclist_head, list) {
+			phdr->p_type = PT_LOAD;
+			phdr->p_flags = PF_R | PF_W | PF_X;
+			phdr->p_offset = kc_vaddr_to_offset(m->addr) + data_offset;
+			phdr->p_vaddr = (size_t)m->addr;
+			if (m->type == KCORE_RAM || m->type == KCORE_TEXT)
+				phdr->p_paddr = __pa(m->addr);
+			else
+				phdr->p_paddr = (elf_addr_t)-1;
+			phdr->p_filesz = phdr->p_memsz = m->size;
+			phdr->p_align = PAGE_SIZE;
+			phdr++;
+		}
+
+		tsz = min_t(size_t, buflen, phdrs_offset + phdrs_len - *fpos);
+		if (copy_to_user(buffer, (char *)phdrs + *fpos - phdrs_offset,
+				 tsz)) {
+			kfree(phdrs);
 			ret = -EFAULT;
 			goto out;
 		}
-		kfree(elf_buf);
+		kfree(phdrs);
+
+		buffer += tsz;
 		buflen -= tsz;
 		*fpos += tsz;
-		buffer += tsz;
+	}
+
+	/* ELF note segment. */
+	if (buflen && *fpos < notes_offset + notes_len) {
+		struct elf_prstatus prstatus = {0};
+		struct elf_prpsinfo prpsinfo = {
+			.pr_sname = 'R',
+			.pr_fname = "vmlinux",
+		};
+		char *notes;
+		size_t i = 0;
+
+		strlcpy(prpsinfo.pr_psargs, saved_command_line,
+			sizeof(prpsinfo.pr_psargs));
+
+		notes = kzalloc(notes_len, GFP_KERNEL);
+		if (!notes) {
+			ret = -ENOMEM;
+			goto out;
+		}
+
+		append_kcore_note(notes, &i, CORE_STR, NT_PRSTATUS, &prstatus,
+				  sizeof(prstatus));
+		append_kcore_note(notes, &i, CORE_STR, NT_PRPSINFO, &prpsinfo,
+				  sizeof(prpsinfo));
+		append_kcore_note(notes, &i, CORE_STR, NT_TASKSTRUCT, current,
+				  arch_task_struct_size);
 
-		/* leave now if filled buffer already */
-		if (buflen == 0)
+		tsz = min_t(size_t, buflen, notes_offset + notes_len - *fpos);
+		if (copy_to_user(buffer, notes + *fpos - notes_offset, tsz)) {
+			kfree(notes);
+			ret = -EFAULT;
 			goto out;
+		}
+		kfree(notes);
+
+		buffer += tsz;
+		buflen -= tsz;
+		*fpos += tsz;
 	}
 
 	/*
 	 * Check to see if our file offset matches with any of
 	 * the addresses in the elf_phdr on our list.
 	 */
-	start = kc_offset_to_vaddr(*fpos - elf_buflen);
+	start = kc_offset_to_vaddr(*fpos - data_offset);
 	if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen)
 		tsz = buflen;
-		
-	while (buflen) {
-		struct kcore_list *m;
 
+	while (buflen) {
 		list_for_each_entry(m, &kclist_head, list) {
 			if (start >= m->addr && start < (m->addr+m->size))
 				break;
@@ -555,7 +488,6 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 	return orig_buflen - buflen;
 }
 
-
 static int open_kcore(struct inode *inode, struct file *filp)
 {
 	if (!capable(CAP_SYS_RAWIO))
-- 
2.18.0

Re: [PATCH 5/7] proc/kcore: clean up ELF header generation

[kbuild test robot]

Hi Omar,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v4.18-rc3 next-20180706]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Omar-Sandoval/proc-kcore-improvements/20180707-052548
reproduce:
        # apt-get install sparse
        make ARCH=x86_64 allmodconfig
        make C=1 CF=-D__CHECK_ENDIAN__


sparse warnings: (new ones prefixed by >>)

   include/linux/nodemask.h:265:16: sparse: expression using sizeof(void)
   include/linux/nodemask.h:271:16: sparse: expression using sizeof(void)
>> fs//proc/kcore.c:328:23: sparse: expression using sizeof(void)
>> fs//proc/kcore.c:328:23: sparse: expression using sizeof(void)
   fs//proc/kcore.c:368:23: sparse: expression using sizeof(void)
   fs//proc/kcore.c:368:23: sparse: expression using sizeof(void)
>> fs//proc/kcore.c:384:49: sparse: missing braces around initializer
   fs//proc/kcore.c:408:23: sparse: expression using sizeof(void)
   fs//proc/kcore.c:408:23: sparse: expression using sizeof(void)

vim +328 fs//proc/kcore.c

   285	
   286	static ssize_t
   287	read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
   288	{
   289		char *buf = file->private_data;
   290		size_t phdrs_offset, notes_offset, data_offset;
   291		size_t phdrs_len, notes_len;
   292		struct kcore_list *m;
   293		size_t tsz;
   294		int nphdr;
   295		unsigned long start;
   296		size_t orig_buflen = buflen;
   297		int ret = 0;
   298	
   299		down_read(&kclist_lock);
   300	
   301		get_kcore_size(&nphdr, &phdrs_len, &notes_len, &data_offset);
   302		phdrs_offset = sizeof(struct elfhdr);
   303		notes_offset = phdrs_offset + phdrs_len;
   304	
   305		/* ELF file header. */
   306		if (buflen && *fpos < sizeof(struct elfhdr)) {
   307			struct elfhdr ehdr = {
   308				.e_ident = {
   309					[EI_MAG0] = ELFMAG0,
   310					[EI_MAG1] = ELFMAG1,
   311					[EI_MAG2] = ELFMAG2,
   312					[EI_MAG3] = ELFMAG3,
   313					[EI_CLASS] = ELF_CLASS,
   314					[EI_DATA] = ELF_DATA,
   315					[EI_VERSION] = EV_CURRENT,
   316					[EI_OSABI] = ELF_OSABI,
   317				},
   318				.e_type = ET_CORE,
   319				.e_machine = ELF_ARCH,
   320				.e_version = EV_CURRENT,
   321				.e_phoff = sizeof(struct elfhdr),
   322				.e_flags = ELF_CORE_EFLAGS,
   323				.e_ehsize = sizeof(struct elfhdr),
   324				.e_phentsize = sizeof(struct elf_phdr),
   325				.e_phnum = nphdr,
   326			};
   327	
 > 328			tsz = min_t(size_t, buflen, sizeof(struct elfhdr) - *fpos);
   329			if (copy_to_user(buffer, (char *)&ehdr + *fpos, tsz)) {
   330				ret = -EFAULT;
   331				goto out;
   332			}
   333	
   334			buffer += tsz;
   335			buflen -= tsz;
   336			*fpos += tsz;
   337		}
   338	
   339		/* ELF program headers. */
   340		if (buflen && *fpos < phdrs_offset + phdrs_len) {
   341			struct elf_phdr *phdrs, *phdr;
   342	
   343			phdrs = kzalloc(phdrs_len, GFP_KERNEL);
   344			if (!phdrs) {
   345				ret = -ENOMEM;
   346				goto out;
   347			}
   348	
   349			phdrs[0].p_type = PT_NOTE;
   350			phdrs[0].p_offset = notes_offset;
   351			phdrs[0].p_filesz = notes_len;
   352	
   353			phdr = &phdrs[1];
   354			list_for_each_entry(m, &kclist_head, list) {
   355				phdr->p_type = PT_LOAD;
   356				phdr->p_flags = PF_R | PF_W | PF_X;
   357				phdr->p_offset = kc_vaddr_to_offset(m->addr) + data_offset;
   358				phdr->p_vaddr = (size_t)m->addr;
   359				if (m->type == KCORE_RAM || m->type == KCORE_TEXT)
   360					phdr->p_paddr = __pa(m->addr);
   361				else
   362					phdr->p_paddr = (elf_addr_t)-1;
   363				phdr->p_filesz = phdr->p_memsz = m->size;
   364				phdr->p_align = PAGE_SIZE;
   365				phdr++;
   366			}
   367	
   368			tsz = min_t(size_t, buflen, phdrs_offset + phdrs_len - *fpos);
   369			if (copy_to_user(buffer, (char *)phdrs + *fpos - phdrs_offset,
   370					 tsz)) {
   371				kfree(phdrs);
   372				ret = -EFAULT;
   373				goto out;
   374			}
   375			kfree(phdrs);
   376	
   377			buffer += tsz;
   378			buflen -= tsz;
   379			*fpos += tsz;
   380		}
   381	
   382		/* ELF note segment. */
   383		if (buflen && *fpos < notes_offset + notes_len) {
 > 384			struct elf_prstatus prstatus = {0};
   385			struct elf_prpsinfo prpsinfo = {
   386				.pr_sname = 'R',
   387				.pr_fname = "vmlinux",
   388			};
   389			char *notes;
   390			size_t i = 0;
   391	
   392			strlcpy(prpsinfo.pr_psargs, saved_command_line,
   393				sizeof(prpsinfo.pr_psargs));
   394	
   395			notes = kzalloc(notes_len, GFP_KERNEL);
   396			if (!notes) {
   397				ret = -ENOMEM;
   398				goto out;
   399			}
   400	
   401			append_kcore_note(notes, &i, CORE_STR, NT_PRSTATUS, &prstatus,
   402					  sizeof(prstatus));
   403			append_kcore_note(notes, &i, CORE_STR, NT_PRPSINFO, &prpsinfo,
   404					  sizeof(prpsinfo));
   405			append_kcore_note(notes, &i, CORE_STR, NT_TASKSTRUCT, current,
   406					  arch_task_struct_size);
   407	
   408			tsz = min_t(size_t, buflen, notes_offset + notes_len - *fpos);
   409			if (copy_to_user(buffer, notes + *fpos - notes_offset, tsz)) {
   410				kfree(notes);
   411				ret = -EFAULT;
   412				goto out;
   413			}
   414			kfree(notes);
   415	
   416			buffer += tsz;
   417			buflen -= tsz;
   418			*fpos += tsz;
   419		}
   420	
   421		/*
   422		 * Check to see if our file offset matches with any of
   423		 * the addresses in the elf_phdr on our list.
   424		 */
   425		start = kc_offset_to_vaddr(*fpos - data_offset);
   426		if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen)
   427			tsz = buflen;
   428	
   429		while (buflen) {
   430			list_for_each_entry(m, &kclist_head, list) {
   431				if (start >= m->addr && start < (m->addr+m->size))
   432					break;
   433			}
   434	
   435			if (&m->list == &kclist_head) {
   436				if (clear_user(buffer, tsz)) {
   437					ret = -EFAULT;
   438					goto out;
   439				}
   440			} else if (m->type == KCORE_VMALLOC) {
   441				vread(buf, (char *)start, tsz);
   442				/* we have to zero-fill user buffer even if no read */
   443				if (copy_to_user(buffer, buf, tsz)) {
   444					ret = -EFAULT;
   445					goto out;
   446				}
   447			} else if (m->type == KCORE_USER) {
   448				/* User page is handled prior to normal kernel page: */
   449				if (copy_to_user(buffer, (char *)start, tsz)) {
   450					ret = -EFAULT;
   451					goto out;
   452				}
   453			} else {
   454				if (kern_addr_valid(start)) {
   455					/*
   456					 * Using bounce buffer to bypass the
   457					 * hardened user copy kernel text checks.
   458					 */
   459					if (probe_kernel_read(buf, (void *) start, tsz)) {
   460						if (clear_user(buffer, tsz)) {
   461							ret = -EFAULT;
   462							goto out;
   463						}
   464					} else {
   465						if (copy_to_user(buffer, buf, tsz)) {
   466							ret = -EFAULT;
   467							goto out;
   468						}
   469					}
   470				} else {
   471					if (clear_user(buffer, tsz)) {
   472						ret = -EFAULT;
   473						goto out;
   474					}
   475				}
   476			}
   477			buflen -= tsz;
   478			*fpos += tsz;
   479			buffer += tsz;
   480			start += tsz;
   481			tsz = (buflen > PAGE_SIZE ? PAGE_SIZE : buflen);
   482		}
   483	
   484	out:
   485		up_write(&kclist_lock);
   486		if (ret)
   487			return ret;
   488		return orig_buflen - buflen;
   489	}
   490	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

Re: [PATCH 5/7] proc/kcore: clean up ELF header generation

[Omar Sandoval]

On Sat, Jul 07, 2018 at 06:05:17PM +0800, kbuild test robot wrote:
> Hi Omar,
> 
> Thank you for the patch! Perhaps something to improve:
> 
> [auto build test WARNING on linus/master]
> [also build test WARNING on v4.18-rc3 next-20180706]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> 
> url:    https://github.com/0day-ci/linux/commits/Omar-Sandoval/proc-kcore-improvements/20180707-052548
> reproduce:
>         # apt-get install sparse
>         make ARCH=x86_64 allmodconfig
>         make C=1 CF=-D__CHECK_ENDIAN__
> 
> 
> sparse warnings: (new ones prefixed by >>)
> 
>    include/linux/nodemask.h:265:16: sparse: expression using sizeof(void)
>    include/linux/nodemask.h:271:16: sparse: expression using sizeof(void)
> >> fs//proc/kcore.c:328:23: sparse: expression using sizeof(void)
> >> fs//proc/kcore.c:328:23: sparse: expression using sizeof(void)

Not sure why this confuses sparse. Maybe because it's #define elfhdr
elf64_hdr.

>    fs//proc/kcore.c:368:23: sparse: expression using sizeof(void)
>    fs//proc/kcore.c:368:23: sparse: expression using sizeof(void)
> >> fs//proc/kcore.c:384:49: sparse: missing braces around initializer

This is

>  > 384			struct elf_prstatus prstatus = {0};

GCC doesn't complain, but I guess I can change it to "= {};", which
isn't strict C89 but both GCC and sparse are happy with.

[PATCH 6/7] proc/kcore: optimize multiple page reads

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

The current code does a full search of the segment list every time for
every page. This is wasteful, since it's almost certain that the next
page will be in the same segment. Instead, check if the previous segment
covers the current page before doing the list search.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 fs/proc/kcore.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index de225b61f34f..f1e21579cd22 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -426,10 +426,18 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 	if ((tsz = (PAGE_SIZE - (start & ~PAGE_MASK))) > buflen)
 		tsz = buflen;
 
+	m = NULL;
 	while (buflen) {
-		list_for_each_entry(m, &kclist_head, list) {
-			if (start >= m->addr && start < (m->addr+m->size))
-				break;
+		/*
+		 * If this is the first iteration or the address is not within
+		 * the previous entry, search for a matching entry.
+		 */
+		if (!m || start < m->addr || start >= m->addr + m->size) {
+			list_for_each_entry(m, &kclist_head, list) {
+				if (start >= m->addr &&
+				    start < m->addr + m->size)
+					break;
+			}
 		}
 
 		if (&m->list == &kclist_head) {
-- 
2.18.0

[PATCH 7/7] proc/kcore: add vmcoreinfo note to /proc/kcore

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

The vmcoreinfo information is useful for runtime debugging tools, not
just for crash dumps. A lot of this information can be determined by
other means, but this is much more convenient.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
 fs/proc/Kconfig            |  1 +
 fs/proc/kcore.c            | 10 ++++++++--
 include/linux/crash_core.h |  2 ++
 kernel/crash_core.c        |  4 ++--
 4 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig
index 0eaeb41453f5..817c02b13b1d 100644
--- a/fs/proc/Kconfig
+++ b/fs/proc/Kconfig
@@ -31,6 +31,7 @@ config PROC_FS
 config PROC_KCORE
 	bool "/proc/kcore support" if !ARM
 	depends on PROC_FS && MMU
+	select CRASH_CORE
 	help
 	  Provides a virtual ELF core file of the live kernel.  This can
 	  be read with gdb and other ELF tools.  No modifications can be
diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index f1e21579cd22..49537c4d78ab 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -10,6 +10,7 @@
  *	Safe accesses to vmalloc/direct-mapped discontiguous areas, Kanoj Sarcar <kanoj@sgi.com>
  */
 
+#include <linux/crash_core.h>
 #include <linux/mm.h>
 #include <linux/proc_fs.h>
 #include <linux/kcore.h>
@@ -81,10 +82,13 @@ static size_t get_kcore_size(int *nphdr, size_t *phdrs_len, size_t *notes_len,
 	}
 
 	*phdrs_len = *nphdr * sizeof(struct elf_phdr);
-	*notes_len = (3 * (sizeof(struct elf_note) + ALIGN(sizeof(CORE_STR), 4)) +
+	*notes_len = (4 * sizeof(struct elf_note) +
+		      3 * ALIGN(sizeof(CORE_STR), 4) +
+		      VMCOREINFO_NOTE_NAME_BYTES +
 		      ALIGN(sizeof(struct elf_prstatus), 4) +
 		      ALIGN(sizeof(struct elf_prpsinfo), 4) +
-		      ALIGN(arch_task_struct_size, 4));
+		      ALIGN(arch_task_struct_size, 4) +
+		      ALIGN(vmcoreinfo_size, 4));
 	*data_offset = PAGE_ALIGN(sizeof(struct elfhdr) + *phdrs_len +
 				  *notes_len);
 	return *data_offset + size;
@@ -404,6 +408,8 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 				  sizeof(prpsinfo));
 		append_kcore_note(notes, &i, CORE_STR, NT_TASKSTRUCT, current,
 				  arch_task_struct_size);
+		append_kcore_note(notes, &i, VMCOREINFO_NOTE_NAME, 0,
+				  vmcoreinfo_data, vmcoreinfo_size);
 
 		tsz = min_t(size_t, buflen, notes_offset + notes_len - *fpos);
 		if (copy_to_user(buffer, notes + *fpos - notes_offset, tsz)) {
diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index b511f6d24b42..525510a9f965 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -60,6 +60,8 @@ phys_addr_t paddr_vmcoreinfo_note(void);
 #define VMCOREINFO_CONFIG(name) \
 	vmcoreinfo_append_str("CONFIG_%s=y\n", #name)
 
+extern unsigned char *vmcoreinfo_data;
+extern size_t vmcoreinfo_size;
 extern u32 *vmcoreinfo_note;
 
 Elf_Word *append_elf_note(Elf_Word *buf, char *name, unsigned int type,
diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index b66aced5e8c2..d02c58b94460 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -14,8 +14,8 @@
 #include <asm/sections.h>
 
 /* vmcoreinfo stuff */
-static unsigned char *vmcoreinfo_data;
-static size_t vmcoreinfo_size;
+unsigned char *vmcoreinfo_data;
+size_t vmcoreinfo_size;
 u32 *vmcoreinfo_note;
 
 /* trusted vmcoreinfo, e.g. we can make a copy in the crash memory */
-- 
2.18.0