From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Jessica Yu <jeyu@redhat.com>, Jiri Kosina <jikos@kernel.org>,
Miroslav Benes <mbenes@suse.cz>,
linux-kernel@vger.kernel.org, live-patching@vger.kernel.org,
Michael Ellerman <mpe@ellerman.id.au>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
x86@kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-s390@vger.kernel.org, Vojtech Pavlik <vojtech@suse.com>,
Jiri Slaby <jslaby@suse.cz>,
Chris J Arges <chris.j.arges@canonical.com>,
Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
Balbir Singh <bsingharora@gmail.com>
Subject: Re: [PATCH v4 01/15] stacktrace/x86: add function for detecting reliable stack traces
Date: Thu, 26 Jan 2017 11:57:44 -0600 [thread overview]
Message-ID: <20170126175744.gv3ttlg52axuq57c@treble> (raw)
In-Reply-To: <20170126135603.GD27517@pathway.suse.cz>
On Thu, Jan 26, 2017 at 02:56:03PM +0100, Petr Mladek wrote:
> On Thu 2017-01-19 09:46:09, Josh Poimboeuf wrote:
> > For live patching and possibly other use cases, a stack trace is only
> > useful if it can be assured that it's completely reliable. Add a new
> > save_stack_trace_tsk_reliable() function to achieve that.
>
> > diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
> > index 0653788..fc36842 100644
> > --- a/arch/x86/kernel/stacktrace.c
> > +++ b/arch/x86/kernel/stacktrace.c
> > @@ -74,6 +74,90 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
> > }
> > EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
> >
> > +#ifdef CONFIG_HAVE_RELIABLE_STACKTRACE
> > +static int __save_stack_trace_reliable(struct stack_trace *trace,
> > + struct task_struct *task)
> > +{
> > + struct unwind_state state;
> > + struct pt_regs *regs;
> > + unsigned long addr;
> > +
> > + for (unwind_start(&state, task, NULL, NULL); !unwind_done(&state);
> > + unwind_next_frame(&state)) {
> > +
> > + regs = unwind_get_entry_regs(&state);
> > + if (regs) {
> > + /*
> > + * Kernel mode registers on the stack indicate an
> > + * in-kernel interrupt or exception (e.g., preemption
> > + * or a page fault), which can make frame pointers
> > + * unreliable.
> > + */
> > + if (!user_mode(regs))
> > + return -1;
> > +
> > + /*
> > + * The last frame contains the user mode syscall
> > + * pt_regs. Skip it and finish the unwind.
> > + */
> > + unwind_next_frame(&state);
> > + if (WARN_ON_ONCE(!unwind_done(&state))) {
> > + show_stack(task, NULL);
>
> We should make sure that show_stack() is called only once as well.
> Otherwise, it would fill logbuffer with random stacktraces without
> any context. It might easily cause flood of messages and the first
> useful one might get lost in the ring buffer.
Agreed.
> > + return -1;
> > + }
> > + break;
> > + }
> > +
> > + addr = unwind_get_return_address(&state);
> > +
> > + /*
> > + * A NULL or invalid return address probably means there's some
> > + * generated code which __kernel_text_address() doesn't know
> > + * about.
> > + */
> > + if (WARN_ON_ONCE(!addr)) {
> > + show_stack(task, NULL);
>
> Same here.
>
> > + return -1;
> > + }
> > +
> > + if (save_stack_address(trace, addr, false))
> > + return -1;
> > + }
> > +
> > + /* Check for stack corruption */
> > + if (WARN_ON_ONCE(unwind_error(&state))) {
> > + show_stack(task, NULL);
>
> And here.
>
> > + return -1;
> > + }
> > +
> > + if (trace->nr_entries < trace->max_entries)
> > + trace->entries[trace->nr_entries++] = ULONG_MAX;
> > +
> > + return 0;
> > +}
> > +
> > +/*
> > + * This function returns an error if it detects any unreliable features of the
> > + * stack. Otherwise it guarantees that the stack trace is reliable.
> > + *
> > + * If the task is not 'current', the caller *must* ensure the task is inactive.
> > + */
> > +int save_stack_trace_tsk_reliable(struct task_struct *tsk,
> > + struct stack_trace *trace)
> > +{
> > + int ret;
> > +
> > + if (!try_get_task_stack(tsk))
> > + return -EINVAL;
> > +
> > + ret = __save_stack_trace_reliable(trace, tsk);
>
> __save_stack_trace_reliable() returns -1 in case of problems.
> But this function returns a meaningful error codes, line -EINVAL,
> -ENOSYS, otherwise.
>
> We should either transform the error code here to something
> "meaningful", probably -EINVAL. Or we should update
> __save_stack_trace_reliable() to return meaningful error codes.
Agreed.
> > + put_task_stack(tsk);
> > +
> > + return ret;
> > +}
> > +#endif /* CONFIG_HAVE_RELIABLE_STACKTRACE */
> > +
> > /* Userspace stacktrace - based on kernel/trace/trace_sysprof.c */
> >
> > struct stack_frame_user {
>
> Otherwise, all the logic looks fine to me. Great work!
Thanks!
--
Josh
next prev parent reply other threads:[~2017-01-26 17:57 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-19 15:46 [PATCH v4 00/15] livepatch: hybrid consistency model Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 01/15] stacktrace/x86: add function for detecting reliable stack traces Josh Poimboeuf
2017-01-26 13:56 ` Petr Mladek
2017-01-26 17:57 ` Josh Poimboeuf [this message]
2017-01-27 8:47 ` Miroslav Benes
2017-01-27 17:13 ` Josh Poimboeuf
2017-02-01 19:57 ` [PATCH v4.1 " Josh Poimboeuf
2017-02-02 14:39 ` Miroslav Benes
2017-01-19 15:46 ` [PATCH v4 02/15] x86/entry: define _TIF_ALLWORK_MASK flags explicitly Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 03/15] livepatch: create temporary klp_update_patch_state() stub Josh Poimboeuf
2017-01-27 8:52 ` Miroslav Benes
2017-01-19 15:46 ` [PATCH v4 04/15] livepatch/x86: add TIF_PATCH_PENDING thread flag Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 05/15] livepatch/powerpc: " Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 06/15] livepatch/s390: reorganize TIF thread flag bits Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 07/15] livepatch/s390: add TIF_PATCH_PENDING thread flag Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 08/15] livepatch: separate enabled and patched states Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 09/15] livepatch: remove unnecessary object loaded check Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 10/15] livepatch: move patching functions into patch.c Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 11/15] livepatch: use kstrtobool() in enabled_store() Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 12/15] livepatch: store function sizes Josh Poimboeuf
2017-01-19 15:46 ` [PATCH v4 13/15] livepatch: change to a per-task consistency model Josh Poimboeuf
2017-02-02 11:45 ` Petr Mladek
2017-02-02 11:47 ` Petr Mladek
2017-02-02 11:51 ` Petr Mladek
2017-02-03 16:21 ` Miroslav Benes
2017-02-03 20:39 ` Josh Poimboeuf
2017-02-06 16:44 ` Petr Mladek
2017-02-06 19:51 ` Josh Poimboeuf
2017-02-08 15:47 ` Petr Mladek
2017-02-08 16:46 ` Josh Poimboeuf
2017-02-09 10:24 ` Petr Mladek
2017-02-03 16:41 ` Miroslav Benes
2017-02-06 15:58 ` Josh Poimboeuf
2017-02-07 8:21 ` Miroslav Benes
2017-01-19 15:46 ` [PATCH v4 14/15] livepatch: add /proc/<pid>/patch_state Josh Poimboeuf
2017-01-31 14:31 ` Miroslav Benes
2017-01-31 14:56 ` Josh Poimboeuf
2017-02-01 8:54 ` Miroslav Benes
2017-01-19 15:46 ` [PATCH v4 15/15] livepatch: allow removal of a disabled patch Josh Poimboeuf
2017-02-03 16:48 ` Miroslav Benes
2017-02-01 20:02 ` [PATCH v4 00/15] livepatch: hybrid consistency model Josh Poimboeuf
2017-02-01 20:52 ` Miroslav Benes
2017-02-01 21:01 ` Jiri Kosina
2017-02-02 14:37 ` Petr Mladek
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170126175744.gv3ttlg52axuq57c@treble \
--to=jpoimboe@redhat.com \
--cc=bsingharora@gmail.com \
--cc=chris.j.arges@canonical.com \
--cc=heiko.carstens@de.ibm.com \
--cc=jeyu@redhat.com \
--cc=jikos@kernel.org \
--cc=jslaby@suse.cz \
--cc=kamalesh@linux.vnet.ibm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=live-patching@vger.kernel.org \
--cc=luto@kernel.org \
--cc=mbenes@suse.cz \
--cc=mingo@kernel.org \
--cc=mpe@ellerman.id.au \
--cc=peterz@infradead.org \
--cc=pmladek@suse.com \
--cc=vojtech@suse.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).