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Date: Fri, 24 Sep 2021 10:17:58 -0700
From: Marios Pomonis <pomonis@...gle.com>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>,
Kees Cook <keescook@...omium.org>,
Alexander Lobakin <alexandr.lobakin@...el.com>,
Kristen C Accardi <kristen.c.accardi@...el.com>,
Sami Tolvanen <samitolvanen@...gle.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <peterz@...radead.org>,
Ivan Babrou <ivan@...udflare.com>,
Jiri Slaby <jirislaby@...nel.org>,
Julien Thierry <jthierry@...hat.com>,
linux-kernel@...r.kernel.org, x86@...nel.org,
linux-hardening@...r.kernel.org
Subject: Re: [PATCH] x86/unwind/orc: Handle kretprobes_trampoline
On Sun, Sep 5, 2021 at 12:57 AM Masami Hiramatsu <mhiramat@...nel.org> wrote:
>
> On Sat, 4 Sep 2021 10:55:11 -0700
> Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> > On Thu, Sep 02, 2021 at 07:13:26PM -0700, Kees Cook wrote:
> > > From: Marios Pomonis <pomonis@...gle.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@...gle.com>
> > > Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> > > Cc: Alexander Lobakin <alexandr.lobakin@...el.com>
> > > Cc: Kristen C Accardi <kristen.c.accardi@...el.com>
> > > Cc: Sami Tolvanen <samitolvanen@...gle.com>
> > > Signed-off-by: Kees Cook <keescook@...omium.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,
I tested this series in conjunction with FG-KASLR and klp_tc_12 fails.
Therefore the patch of the cover mail fixes a different issue than the
one of this series.
Thanks,
Marios
> >
> >
> > > ---
> > > 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@...nel.org>
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