Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754991AbcKKKTf (ORCPT ); Fri, 11 Nov 2016 05:19:35 -0500 Received: from mail.skyhub.de ([78.46.96.112]:56089 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754170AbcKKKTd (ORCPT ); Fri, 11 Nov 2016 05:19:33 -0500 From: Borislav Petkov To: X86 ML Cc: LKML , Andy Lutomirski , Linus Torvalds , Peter Zijlstra Subject: [RFC PATCH] x86/debug: Dump more detailed segfault info Date: Fri, 11 Nov 2016 11:19:30 +0100 Message-Id: <20161111101930.32559-1-bp@alien8.de> X-Mailer: git-send-email 2.10.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3396 Lines: 92 From: Borislav Petkov I found out recently that this is very helpful when trying to look at opcodes around the rIP when the segfault happens, and also poke at architectural registers. When enabled, it looks something like this: strsep[3702]: segfault at 40066b ip 00007ffff7abe22b sp 00007fffffffea70 error 7 in libc-2.19.so[7ffff7a33000+19f000] RIP: 0033:[<00007ffff7abe22b>] [<00007ffff7abe22b>] 0x7ffff7abe22b RSP: 002b:00007fffffffea70 EFLAGS: 00010202 RAX: 000000000040066b RBX: 0000000000400664 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 000000000000003d RDI: 0000000000400665 RBP: 00007fffffffea90 R08: 00007ffff7dd7c60 R09: 00007ffff7deae20 R10: 00007fffffffe850 R11: 00007ffff7abe200 R12: 0000000000400460 R13: 00007fffffffeb80 R14: 0000000000000000 R15: 0000000000000000 FS: 00007ffff7fdc700(0000) GS:ffff88007ed40000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000000040066b CR3: 0000000079a39000 CR4: 00000000000406e0 Code: 74 33 80 7e 01 00 74 22 48 89 df e8 5a 8a ff ff 48 85 c0 74 20 00 00 48 83 c0 01 48 89 45 00 48 89 d8 48 83 c4 08 5b 5d c3 0f b6 13 38 d0 74 29 84 d2 75 15 48 c7 45 00 00 00 00 00 48 83 c4 I know, this info can be collected with core dumps but in constrained environments or when writing out core dumps is impossible (too early in the boot, fs is fscked), getting some more detailed info might be really helpful. Oh, and the size of the change is small enough. Signed-off-by: Borislav Petkov Cc: Andy Lutomirski Cc: Linus Torvalds Cc: Peter Zijlstra --- arch/x86/Kconfig.debug | 9 +++++++++ arch/x86/mm/fault.c | 24 +++++++++++++++++++++++- 2 files changed, 32 insertions(+), 1 deletion(-) diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug index 67eec55093a5..514bbae2f4c6 100644 --- a/arch/x86/Kconfig.debug +++ b/arch/x86/Kconfig.debug @@ -361,4 +361,13 @@ config PUNIT_ATOM_DEBUG The current power state can be read from /sys/kernel/debug/punit_atom/dev_power_state +config SEGFAULT_DETAILED_DEBUG + bool "Dump detailed information for fatal segfaults" + ---help--- + Enable this option if you want to see more debug info in + the kernel log when fatal segfaults get reported. This + option might be useful in constrained environments when + core dumps might not be possible and/or filesystems are + not ready for a core dump writeout. + endmenu diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 9f72ca3b2669..120f126f5b54 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -847,8 +847,30 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code, (void *)regs->ip, (void *)regs->sp, error_code); print_vma_addr(KERN_CONT " in ", regs->ip); - printk(KERN_CONT "\n"); + + if (IS_ENABLED(CONFIG_SEGFAULT_DETAILED_DEBUG)) { +#define PREAMBLE_LEN 21 +#define OPC_BUF_LEN 64 + u8 code[OPC_BUF_LEN]; + int len, i; + + len = __copy_from_user_inatomic(code, + (void *)regs->ip - PREAMBLE_LEN, + OPC_BUF_LEN); + + __show_regs(regs, 1); + + printk(KERN_DEFAULT "Code: "); + for (i = 0; i < OPC_BUF_LEN - len; i++) { + if (i == PREAMBLE_LEN) + pr_cont("<%02x> ", code[i]); + else + pr_cont("%02x ", code[i]); + } + + printk(KERN_CONT "\n"); + } } static void -- 2.10.0