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Subject[PATCH v3 8/8] proc/kcore: add vmcoreinfo note to /proc/kcore
Date
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, and it only adds a page
at most to the file.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
fs/proc/Kconfig | 1 +
fs/proc/kcore.c | 18 ++++++++++++++++--
include/linux/crash_core.h | 2 ++
kernel/crash_core.c | 4 ++--
4 files changed, 21 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 25fefdd05ee5..ab7c1a1dad50 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)) {
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
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