On Thu, Sep 29, 2022 at 10:12:27AM -0400, Mathieu Desnoyers wrote: > These commits use WARN_ON_ONCE() and kill the offending processes when > deprecated and unknown flags are encountered: > > commit c17a6ff93213 ("rseq: Kill process when unknown flags are encountered in ABI structures") > commit 0190e4198e47 ("rseq: Deprecate RSEQ_CS_FLAG_NO_RESTART_ON_* flags") > > The WARN_ON_ONCE() triggered by userspace input prevents use of > Syzkaller to fuzz the rseq system call. > > Replace this WARN_ON_ONCE() by pr_warn_once() messages which contain > actually useful information. > > Reported-by: Mark Rutland <mark.rutland@xxxxxxx> > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> Thanks for this! I've set off a Syzkaller run with this applied, and I'll be able to tell you in a day or two whether that's made it possible to spot anything more interesting. Regardless, I think this is a good change, so FWIW: Acked-by: Mark Rutland <mark.rutland@xxxxxxx> Mark. > --- > kernel/rseq.c | 19 +++++++++++++++++-- > 1 file changed, 17 insertions(+), 2 deletions(-) > > diff --git a/kernel/rseq.c b/kernel/rseq.c > index bda8175f8f99..d38ab944105d 100644 > --- a/kernel/rseq.c > +++ b/kernel/rseq.c > @@ -171,12 +171,27 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs) > return 0; > } > > +static bool rseq_warn_flags(const char *str, u32 flags) > +{ > + u32 test_flags; > + > + if (!flags) > + return false; > + test_flags = flags & RSEQ_CS_NO_RESTART_FLAGS; > + if (test_flags) > + pr_warn_once("Deprecated flags (%u) in %s ABI structure", test_flags, str); > + test_flags = flags & ~RSEQ_CS_NO_RESTART_FLAGS; > + if (test_flags) > + pr_warn_once("Unknown flags (%u) in %s ABI structure", test_flags, str); > + return true; > +} > + > static int rseq_need_restart(struct task_struct *t, u32 cs_flags) > { > u32 flags, event_mask; > int ret; > > - if (WARN_ON_ONCE(cs_flags & RSEQ_CS_NO_RESTART_FLAGS) || cs_flags) > + if (rseq_warn_flags("rseq_cs", cs_flags)) > return -EINVAL; > > /* Get thread flags. */ > @@ -184,7 +199,7 @@ static int rseq_need_restart(struct task_struct *t, u32 cs_flags) > if (ret) > return ret; > > - if (WARN_ON_ONCE(flags & RSEQ_CS_NO_RESTART_FLAGS) || flags) > + if (rseq_warn_flags("rseq", flags)) > return -EINVAL; > > /* > -- > 2.30.2 >