Hi Mathieu, On Thu, Jun 28, 2018 at 12:23:59PM -0400, Mathieu Desnoyers wrote: > On 32-bit kernels, the rseq->rseq_cs_padding field is never read by the > kernel. However, 64-bit kernels dealing with 32-bit compat tasks read the > full 64-bit in its entirety, and terminates the offending process with > a segmentation fault if the upper 32 bits are set due to failure of > copy_from_user(). > > Ensure that both 32-bit and 64-bit kernels dealing with 32-bit tasks end > up terminating offending tasks with a segmentation fault if the upper > 32-bit padding bits (rseq->rseq_cs_padding) are set by adding an explicit > check that padding is zero on 32-bit kernels. > > Signed-off-by: Mathieu Desnoyers <[email protected]> > CC: "Paul E. McKenney" <[email protected]> > CC: Peter Zijlstra <[email protected]> > CC: Paul Turner <[email protected]> > CC: Thomas Gleixner <[email protected]> > CC: Andy Lutomirski <[email protected]> > CC: Andi Kleen <[email protected]> > CC: Dave Watson <[email protected]> > CC: Chris Lameter <[email protected]> > CC: Ingo Molnar <[email protected]> > CC: "H. Peter Anvin" <[email protected]> > CC: Ben Maurer <[email protected]> > CC: Steven Rostedt <[email protected]> > CC: Josh Triplett <[email protected]> > CC: Linus Torvalds <[email protected]> > CC: Andrew Morton <[email protected]> > CC: Russell King <[email protected]> > CC: Catalin Marinas <[email protected]> > CC: Will Deacon <[email protected]> > CC: Michael Kerrisk <[email protected]> > CC: Boqun Feng <[email protected]> > CC: [email protected] > --- > kernel/rseq.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/kernel/rseq.c b/kernel/rseq.c > index 4ba582046fcd..b038f35a60d6 100644 > --- a/kernel/rseq.c > +++ b/kernel/rseq.c > @@ -112,6 +112,29 @@ static int rseq_reset_rseq_cpu_id(struct task_struct *t) > return 0; > } > > +#ifndef __LP64__ > +/* > + * Ensure that padding is zero. > + */ > +static int check_rseq_cs_padding(struct task_struct *t) > +{ > + unsigned long pad; > + int ret; > + > + ret = __get_user(pad, &t->rseq->rseq_cs_padding); > + if (ret) > + return ret; > + if (pad) > + return -EFAULT; > + return 0; > +} > +#else > +static int check_rseq_cs_padding(struct task_struct *t) > +{ > + return 0; > +} > +#endif
I'm still not sure how this works with a 64-bit kernel and a compat (32-bit) task. The check_rseq_cs_padding() will return 0 regardless of the upper bits of the rseq_cs field, whereas a native 32-bit kernel would actually go and check them. What am I missing here? Will
