From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754254AbcFPL4x (ORCPT ); Thu, 16 Jun 2016 07:56:53 -0400 Received: from mail.skyhub.de ([78.46.96.112]:51637 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753850AbcFPL4w (ORCPT ); Thu, 16 Jun 2016 07:56:52 -0400 Date: Thu, 16 Jun 2016 13:56:48 +0200 From: Borislav Petkov To: Andy Lutomirski Cc: "linux-kernel@vger.kernel.org" , x86@kernel.org, Nadav Amit , Kees Cook , Brian Gerst , "kernel-hardening@lists.openwall.com" , Linus Torvalds , Josh Poimboeuf Subject: Re: [PATCH 09/13] x86/dumpstack: When dumping stack bytes due to OOPS, start with regs->sp Message-ID: <20160616115648.GB4688@pd.tnic> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 15, 2016 at 05:28:31PM -0700, Andy Lutomirski wrote: > The comment suggests that show_stack(NULL, NULL) should backtrace > the current context, but the code doesn't match the comment. If > regs are given, start the "Stack:" hexdump at regs->sp. > > Signed-off-by: Andy Lutomirski Very nice: [ 0.020008] unchecked MSR access error: RDMSR from 0x1b0 at rIP: 0xffffffff8102849f (init_intel_energy_perf.part.3+0xf/0xd0) [ 0.024003] 0000000000000000 ffffffff81c03f10 ffffffff81028a2f 0000000000000000 [ 0.028799] ffffffff81cad5e0 ffffffff81d5e920 ffffffff81c03f38 ffffffff810271f5 [ 0.034887] ffffffffffffffff ffff88007efd18c0 ffffffff81d5e920 ffffffff81c03f48 [ 0.038883] Call Trace: [ 0.040009] [] init_intel+0xdf/0x2b0 [ 0.042055] [] identify_cpu+0x2f5/0x4f0 [ 0.044005] [] identify_boot_cpu+0x10/0x7a [ 0.045577] [] check_bugs+0x9/0x2d [ 0.047033] [] start_kernel+0x3bd/0x3d9 [ 0.048005] [] x86_64_start_reservations+0x2f/0x31 [ 0.049668] [] x86_64_start_kernel+0x168/0x176 That's exactly what I wanted to see! Thanks for the hints. Here's what I did: --- diff --git a/arch/x86/include/asm/kdebug.h b/arch/x86/include/asm/kdebug.h index e5f5dc9787d5..1ef9d581b5d9 100644 --- a/arch/x86/include/asm/kdebug.h +++ b/arch/x86/include/asm/kdebug.h @@ -26,6 +26,7 @@ extern void die(const char *, struct pt_regs *,long); extern int __must_check __die(const char *, struct pt_regs *, long); extern void show_trace(struct task_struct *t, struct pt_regs *regs, unsigned long *sp, unsigned long bp); +extern void show_stack_regs(struct pt_regs *regs); extern void __show_regs(struct pt_regs *regs, int all); extern unsigned long oops_begin(void); extern void oops_end(unsigned long, struct pt_regs *, int signr); diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c index 400a2e17c1d1..0c3436535b4a 100644 --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -206,6 +206,11 @@ void show_stack(struct task_struct *task, unsigned long *sp) show_stack_log_lvl(task, NULL, sp, bp, ""); } +void show_stack_regs(struct pt_regs *regs) +{ + show_stack_log_lvl(current, regs, (unsigned long *)regs->sp, regs->bp, ""); +} + static arch_spinlock_t die_lock = __ARCH_SPIN_LOCK_UNLOCKED; static int die_owner = -1; static unsigned int die_nest_count; diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c index 4bb53b89f3c5..fafc771568c7 100644 --- a/arch/x86/mm/extable.c +++ b/arch/x86/mm/extable.c @@ -1,6 +1,7 @@ #include #include #include +#include typedef bool (*ex_handler_t)(const struct exception_table_entry *, struct pt_regs *, int); @@ -46,8 +47,9 @@ EXPORT_SYMBOL(ex_handler_ext); bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup, struct pt_regs *regs, int trapnr) { - WARN_ONCE(1, "unchecked MSR access error: RDMSR from 0x%x\n", - (unsigned int)regs->cx); + if (pr_warn_once("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pF)\n", + (unsigned int)regs->cx, regs->ip, (void *)regs->ip)) + show_stack_regs(regs); /* Pretend that the read succeeded and returned 0. */ regs->ip = ex_fixup_addr(fixup); @@ -60,9 +62,10 @@ EXPORT_SYMBOL(ex_handler_rdmsr_unsafe); bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup, struct pt_regs *regs, int trapnr) { - WARN_ONCE(1, "unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x)\n", - (unsigned int)regs->cx, - (unsigned int)regs->dx, (unsigned int)regs->ax); + if (pr_warn_once("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pF)\n", + (unsigned int)regs->cx, (unsigned int)regs->dx, + (unsigned int)regs->ax, regs->ip, (void *)regs->ip)) + show_stack_regs(regs); /* Pretend that the write succeeded. */ regs->ip = ex_fixup_addr(fixup); diff --git a/include/linux/printk.h b/include/linux/printk.h index f4da695fd615..0a961657e2a0 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -309,20 +309,25 @@ extern asmlinkage void dump_stack(void) __cold; #define printk_once(fmt, ...) \ ({ \ static bool __print_once __read_mostly; \ + int __ret_print_once = !__print_once; \ \ if (!__print_once) { \ __print_once = true; \ printk(fmt, ##__VA_ARGS__); \ } \ + __ret_print_once; \ }) + #define printk_deferred_once(fmt, ...) \ ({ \ static bool __print_once __read_mostly; \ + int __ret_print_once = !__print_once; \ \ if (!__print_once) { \ __print_once = true; \ printk_deferred(fmt, ##__VA_ARGS__); \ } \ + __ret_print_once; \ }) #else #define printk_once(fmt, ...) \ -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply.