Re: [PATCH] x86/unwind/orc: Handle kretprobes_trampoline

[Masami Hiramatsu <mhiramat@kernel.org>]

On Sat, 4 Sep 2021 10:55:11 -0700
Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> On Thu, Sep 02, 2021 at 07:13:26PM -0700, Kees Cook wrote:
> > From: Marios Pomonis <pomonis@google.com>
> > 
> > Fix a bug in the ORC unwinder when kretprobes has replaced a return
> > address with the address of `kretprobes_trampoline'. ORC mistakenly
> > assumes that the address in the stack is a return address and decrements
> > it by 1 in order to find the proper depth of the next frame.
> > 
> > This issue was discovered while testing the FG-KASLR series[0][1] and
> > running the live patching test[2] that was originally failing[3].
> > 
> > [0] https://lore.kernel.org/kernel-hardening/20200923173905.11219-1-kristen@linux.intel.com/
> > [1] https://github.com/KSPP/linux/issues/132
> > [2] https://github.com/lpechacek/qa_test_klp
> > [3] https://lore.kernel.org/lkml/alpine.LSU.2.21.2009251450260.13615@pobox.suse.cz/
> > 
> > Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
> > Signed-off-by: Marios Pomonis <pomonis@google.com>
> > Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> > Cc: Alexander Lobakin <alexandr.lobakin@intel.com>
> > Cc: Kristen C Accardi <kristen.c.accardi@intel.com>
> > Cc: Sami Tolvanen <samitolvanen@google.com>
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> 
> I suspect this is fixed by:
> 
>   https://lkml.kernel.org/r/162756755600.301564.4957591913842010341.stgit@devnote2

I think this can be a bit different issue. As far as I ran my test code
(same one in the above cover mail) with this fix, the stacktrace wasn't
fixed.

ffffffff812b7c80  r  vfs_read+0x0    [FTRACE]
ffffffff813b4cc0  r  full_proxy_read+0x0    [FTRACE]
# tracer: nop
#
# entries-in-buffer/entries-written: 3/3   #P:8
#
#                                _-----=> irqs-off
#                               / _----=> need-resched
#                              | / _---=> hardirq/softirq
#                              || / _--=> preempt-depth
#                              ||| /     delay
#           TASK-PID     CPU#  ||||   TIMESTAMP  FUNCTION
#              | |         |   ||||      |         |
             cat-138     [002] ...1     9.488727: r_full_proxy_read_0: (vfs_read+0x99/0x190 <- full_proxy_read)
             cat-138     [002] ...1     9.488732: <stack trace>
 => kretprobe_trace_func+0x209/0x300
 => kretprobe_dispatcher+0x9d/0xb0
 => __kretprobe_trampoline_handler+0xc5/0x160
 => trampoline_handler+0x44/0x60
 => kretprobe_trampoline+0x25/0x50
             cat-138     [002] ...1     9.488733: r_vfs_read_0: (ksys_read+0x68/0xe0 <- vfs_read)

Kees, can you also try to test with my series?
It should be able to be checked out with;

git clone git://git.kernel.org/pub/scm/linux/kernel/git/mhiramat/linux.git -b kprobes/kretprobe-stackfix-v10

Thank you,
> 
> 
> > ---
> >  arch/x86/kernel/unwind_orc.c | 12 +++++++++++-
> >  1 file changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
> > index a1202536fc57..8c5038b3b707 100644
> > --- a/arch/x86/kernel/unwind_orc.c
> > +++ b/arch/x86/kernel/unwind_orc.c
> > @@ -7,6 +7,7 @@
> >  #include <asm/unwind.h>
> >  #include <asm/orc_types.h>
> >  #include <asm/orc_lookup.h>
> > +#include <asm/kprobes.h>
> >  
> >  #define orc_warn(fmt, ...) \
> >  	printk_deferred_once(KERN_WARNING "WARNING: " fmt, ##__VA_ARGS__)
> > @@ -414,6 +415,15 @@ static bool get_reg(struct unwind_state *state, unsigned int reg_off,
> >  	return false;
> >  }
> >  
> > +static bool is_kretprobe_trampoline(unsigned long ip)
> > +{
> > +#ifdef	CONFIG_KRETPROBES
> > +	if (ip == (unsigned long)&kretprobe_trampoline)
> > +		return true;
> > +#endif
> > +	return false;
> > +}
> > +
> >  bool unwind_next_frame(struct unwind_state *state)
> >  {
> >  	unsigned long ip_p, sp, tmp, orig_ip = state->ip, prev_sp = state->sp;
> > @@ -540,7 +550,7 @@ bool unwind_next_frame(struct unwind_state *state)
> >  		state->sp = sp;
> >  		state->regs = NULL;
> >  		state->prev_regs = NULL;
> > -		state->signal = false;
> > +		state->signal = is_kretprobe_trampoline(state->ip);
> >  		break;
> >  
> >  	case UNWIND_HINT_TYPE_REGS:
> > -- 
> > 2.30.2
> > 
> 
> -- 
> Josh
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>