[PATCH v2] kexec: Introduce vmcoreinfo signature verification

Xunlei Pang
2017-03-17T03:42:56Z

Currently vmcoreinfo data is updated at boot time subsys_initcall(),
it has the risk of being modified by some wrong code during system
is running.

As a result, vmcore dumped may contain the wrong vmcoreinfo. Later on,
when using "crash" or "makedumpfile"(etc) utility to parse this vmcore,
we probably will get "Segmentation fault" or other unexpected/confusing
errors.

As vmcoreinfo is the most fundamental information for vmcore, we better
double check its correctness. Here we generate a signature(using crc32)
after it is saved, then verify it in crash_save_vmcoreinfo() to see if
the signature was broken, if so we have to re-save the vmcoreinfo data
to get the correct vmcoreinfo for kdump as possible as we can.

Signed-off-by: Xunlei Pang <xlpang@redhat.com>
---
v1->v2:
- Keep crash_save_vmcoreinfo_init() because "makedumpfile --mem-usage"
uses the information.
- Add crc32 verification for vmcoreinfo, re-save when failure.

arch/Kconfig | 1 +
kernel/kexec_core.c | 43 +++++++++++++++++++++++++++++++++++--------
2 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index c4d6833..66eb296 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -4,6 +4,7 @@

config KEXEC_CORE
bool
+ select CRC32

config HAVE_IMA_KEXEC
bool
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index bfe62d5..012acbe 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -38,6 +38,7 @@
#include <linux/syscore_ops.h>
#include <linux/compiler.h>
#include <linux/hugetlb.h>
+#include <linux/crc32.h>

#include <asm/page.h>
#include <asm/sections.h>
@@ -53,9 +54,10 @@

/* vmcoreinfo stuff */
static unsigned char vmcoreinfo_data[VMCOREINFO_BYTES];
-u32 vmcoreinfo_note[VMCOREINFO_NOTE_SIZE/4];
+static u32 vmcoreinfo_sig;
size_t vmcoreinfo_size;
size_t vmcoreinfo_max_size = sizeof(vmcoreinfo_data);
+u32 vmcoreinfo_note[VMCOREINFO_NOTE_SIZE/4];

/* Flag to indicate we are going to kexec a new kernel */
bool kexec_in_progress = false;
@@ -1367,12 +1369,6 @@ static void update_vmcoreinfo_note(void)
final_note(buf);
}

-void crash_save_vmcoreinfo(void)
-{
- vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
- update_vmcoreinfo_note();
-}
-
void vmcoreinfo_append_str(const char *fmt, ...)
{
va_list args;
@@ -1402,7 +1398,7 @@ phys_addr_t __weak paddr_vmcoreinfo_note(void)
return __pa_symbol((unsigned long)(char *)&vmcoreinfo_note);
}

-static int __init crash_save_vmcoreinfo_init(void)
+static void do_crash_save_vmcoreinfo_init(void)
{
VMCOREINFO_OSRELEASE(init_uts_ns.name.release);
VMCOREINFO_PAGESIZE(PAGE_SIZE);
@@ -1474,6 +1470,37 @@ static int __init crash_save_vmcoreinfo_init(void)
#endif

arch_crash_save_vmcoreinfo();
+}
+
+static u32 crash_calc_vmcoreinfo_sig(void)
+{
+ return crc32(~0, vmcoreinfo_data, vmcoreinfo_size);
+}
+
+static bool crash_verify_vmcoreinfo(void)
+{
+ if (crash_calc_vmcoreinfo_sig() == vmcoreinfo_sig)
+ return true;
+
+ return false;
+}
+
+void crash_save_vmcoreinfo(void)
+{
+ /* Re-save if verification fails */
+ if (!crash_verify_vmcoreinfo()) {
+ vmcoreinfo_size = 0;
+ do_crash_save_vmcoreinfo_init();
+ }
+
+ vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
+ update_vmcoreinfo_note();
+}
+
+static int __init crash_save_vmcoreinfo_init(void)
+{
+ do_crash_save_vmcoreinfo_init();
+ vmcoreinfo_sig = crash_calc_vmcoreinfo_sig();
update_vmcoreinfo_note();

return 0;
--
1.8.3.1