From: Eiichi Tsukata <devel@etsukata.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Andrew Lutomirski <luto@kernel.org>, Peter Anvin <hpa@zytor.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Juergen Gross <jgross@suse.com>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
He Zhe <zhe.he@windriver.com>,
Joel Fernandes <joel@joelfernandes.org>
Subject: Re: [PATCH v2 5/7] x86/mm, tracing: Fix CR2 corruption
Date: Sat, 6 Jul 2019 20:07:22 +0900 [thread overview]
Message-ID: <a4a50e28-d972-3cef-b668-1e49d5b5496f@etsukata.com> (raw)
In-Reply-To: <CAHk-=wiJ4no+TW-8KTfpO-Q5+aaTGVoBJzrnFTvj_zGpVbrGfA@mail.gmail.com>
On 2019/07/05 11:18, Linus Torvalds wrote:
> On Fri, Jul 5, 2019 at 5:03 AM Peter Zijlstra <peterz@infradead.org> wrote:
>>
>> Despire the current efforts to read CR2 before tracing happens there
>> still exist a number of possible holes:
>
> So this whole series disturbs me for the simple reason that I thought
> tracing was supposed to save/restore cr2 and make it unnecessary to
> worry about this in non-tracing code.
>
> That is very much what the NMI code explicitly does. Why shouldn't all
> the other tracing code do the same thing in case they can take page
> faults?
>
> So I don't think the patches are wrong per se, but this seems to solve
> it at the wrong level.
>
> Linus
>
Steven previously tried to fix it by saving CR2 in TRACE_IRQS_OFF:
https://lore.kernel.org/lkml/20190320221534.165ab87b@oasis.local.home/
But hit the following WARNING:
https://lore.kernel.org/lkml/20190321095502.47b51356@gandalf.local.home/
I tried to find out the root cause of the WARNING, and found that it is
caused by touching trace point(TRACE_IRQS_OFF) before search_binary_handler()
at exeve.
To prevent userstack trace code from reading user stack before it becomes ready,
checking current->in_execve in stack_trace_save_user() can help Steven's approach,
though trace_sched_process_exec() is called before current->in_execve = 0 so it changes
current behavior.
The PoC code is as follows:
diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 2abf27d7df6b..30fa6e1b7a87 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -116,10 +116,12 @@ void arch_stack_walk_user(stack_trace_consume_fn consume_entry, void *cookie,
const struct pt_regs *regs)
{
const void __user *fp = (const void __user *)regs->bp;
+ unsigned long address;
if (!consume_entry(cookie, regs->ip, false))
return;
+ address = read_cr2();
while (1) {
struct stack_frame_user frame;
@@ -131,11 +133,14 @@ void arch_stack_walk_user(stack_trace_consume_fn consume_entry, void *cookie,
break;
if (frame.ret_addr) {
if (!consume_entry(cookie, frame.ret_addr, false))
- return;
+ break;
}
if (fp == frame.next_fp)
break;
fp = frame.next_fp;
}
+
+ if (address != read_cr2())
+ write_cr2(address);
}
diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 36139de0a3c4..489d33bb5d28 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -230,6 +230,9 @@ unsigned int stack_trace_save_user(unsigned long *store, unsigned int size)
/* Trace user stack if not a kernel thread */
if (!current->mm)
return 0;
+ /* current can reach some trace points before its stack is ready */
+ if (current->in_execve)
+ return 0;
arch_stack_walk_user(consume_entry, &c, task_pt_regs(current));
return c.len;
next prev parent reply other threads:[~2019-07-06 11:07 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-04 19:55 [PATCH v2 0/7] Tracing vs CR2 (and cleanups) Peter Zijlstra
2019-07-04 19:55 ` [PATCH v2 1/7] x86/paravirt: Make read_cr2() CALLEE_SAVE Peter Zijlstra
2019-07-04 21:49 ` Andy Lutomirski
2019-07-10 19:53 ` Steven Rostedt
2019-07-04 19:55 ` [PATCH v2 2/7] x86/entry/32: Simplify common_exception Peter Zijlstra
2019-07-04 21:51 ` Andy Lutomirski
2019-07-10 20:11 ` Steven Rostedt
2019-07-10 20:14 ` Peter Zijlstra
2019-07-04 19:55 ` [PATCH v2 3/7] x86/entry/64: Simplify idtentry a little Peter Zijlstra
2019-07-04 21:54 ` Andy Lutomirski
2019-07-10 20:23 ` Steven Rostedt
2019-07-04 19:55 ` [PATCH v2 4/7] x86/entry/64: Update comments and sanity tests for create_gap Peter Zijlstra
2019-07-04 21:55 ` Andy Lutomirski
2019-07-10 20:24 ` Steven Rostedt
2019-07-04 19:56 ` [PATCH v2 5/7] x86/mm, tracing: Fix CR2 corruption Peter Zijlstra
2019-07-05 2:18 ` Linus Torvalds
2019-07-05 3:16 ` Andy Lutomirski
2019-07-05 3:27 ` Linus Torvalds
2019-07-05 13:49 ` Peter Zijlstra
2019-07-06 21:41 ` Linus Torvalds
2019-07-06 22:27 ` Steven Rostedt
2019-07-06 22:41 ` Linus Torvalds
2019-07-07 0:08 ` Linus Torvalds
2019-07-07 0:36 ` Andy Lutomirski
2019-07-06 23:50 ` Andy Lutomirski
2019-07-07 3:44 ` Eiichi Tsukata
2019-07-06 11:07 ` Eiichi Tsukata [this message]
2019-07-08 7:48 ` Peter Zijlstra
2019-07-08 8:58 ` Eiichi Tsukata
2019-07-08 9:42 ` Eiichi Tsukata
2019-07-09 5:17 ` Eiichi Tsukata
2019-07-07 15:10 ` Andy Lutomirski
2019-07-07 15:11 ` Andy Lutomirski
2019-07-07 18:17 ` Linus Torvalds
2019-07-10 20:27 ` Steven Rostedt
2019-07-11 6:45 ` Greg Kroah-Hartman
2019-07-11 12:12 ` Sasha Levin
2019-07-11 12:21 ` Peter Zijlstra
2019-07-04 19:56 ` [PATCH v2 6/7] x86/entry/64: Remove TRACE_IRQS_*_DEBUG Peter Zijlstra
2019-07-11 3:24 ` Steven Rostedt
2019-07-11 8:05 ` Peter Zijlstra
2019-07-04 19:56 ` [RFC][PATCH v2 7/7] x86/entry/64: Pull bits into C Peter Zijlstra
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