proc/kcore: add vmcoreinfo note to /proc/kcore

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, and it only adds a page at most
to the file.

Link: http://lkml.kernel.org/r/fddbcd08eed76344863303878b12de1c1e2a04b6.1531953780.git.osandov@fb.com
Signed-off-by: Omar Sandoval <osandov@fb.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Bhupesh Sharma <bhsharma@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: James Morse <james.morse@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 2 deletions

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index 758c14e46a44..80464432dfe6 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;
@@ -406,6 +410,16 @@ 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);
+                /*
+                 * vmcoreinfo_size is mostly constant after init time, but it
+                 * can be changed by crash_save_vmcoreinfo(). Racing here with a
+                 * panic on another CPU before the machine goes down is insanely
+                 * unlikely, but it's better to not leave potential buffer
+                 * overflows lying around, regardless.
+                 */
+                append_kcore_note(notes, &i, VMCOREINFO_NOTE_NAME, 0,
+                                  vmcoreinfo_data,
+                                  min(vmcoreinfo_size, notes_len - i));
 
                 tsz = min_t(size_t, buflen, notes_offset + notes_len - *fpos);
                 if (copy_to_user(buffer, notes + *fpos - notes_offset, tsz)) {