[PATCH 6/9] x86/fault: Dump user opcode bytes on fatal faults

Borislav Petkov
2018-04-17T16:13:59Z

Sometimes it is useful to see which user opcode bytes RIP points to
when a fault happens: be it to rule out RIP corruption, to dump info
early during boot, when doing core dumps is impossible due to not having
writable fs yet.

Sometimes it is useful if debugging an issue and one doesn't have access
to the executable which caused the fault in order to disassemble it.

That last aspect might have some security implications so
show_unhandled_signals could be revisited for that or a new config
option added.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/mm/fault.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 73bd8c95ac71..a3fd94eff04d 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -828,6 +828,8 @@ static inline void
show_signal_msg(struct pt_regs *regs, unsigned long error_code,
unsigned long address, struct task_struct *tsk)
{
+ const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG;
+
if (!unhandled_signal(tsk, SIGSEGV))
return;

@@ -835,13 +837,14 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code,
return;

printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx",
- task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
- tsk->comm, task_pid_nr(tsk), address,
+ loglvl, tsk->comm, task_pid_nr(tsk), address,
(void *)regs->ip, (void *)regs->sp, error_code);

print_vma_addr(KERN_CONT " in ", regs->ip);

printk(KERN_CONT "\n");
+
+ show_opcodes((u8 *)regs->ip, loglvl);
}

static void
--
2.13.0