Messages in this thread | | | Date | Mon, 2 Jul 2018 17:03:44 -0400 (EDT) | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH for 4.18 1/2] rseq: use __u64 for rseq_cs fields, validate abort_ip < TASK_SIZE |
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----- On Jul 2, 2018, at 4:52 PM, Linus Torvalds torvalds@linux-foundation.org wrote:
> On Mon, Jul 2, 2018 at 1:41 PM Mathieu Desnoyers > <mathieu.desnoyers@efficios.com> wrote: >> >> - if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs))) >> + if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs)) || >> + rseq_cs->abort_ip >= TASK_SIZE) >> return -EFAULT; > > I think the abort_ip check should have the same error value as the > other sanity checks, ie just be of this format: > >> if (rseq_cs->version > 0) >> return -EINVAL;
OK, so I'll go for -EINVAL.
> > also, I think you should check start_ip to be consistent. You kind of > accidentally do it with the check for > > if (rseq_cs->abort_ip - rseq_cs->start_ip - rseq_cs->post_commit_offset)
The check is actually:
/* Ensure that abort_ip is not in the critical section. */ if (rseq_cs->abort_ip - rseq_cs->start_ip < rseq_cs->post_commit_offset) return -EINVAL;
> > but honestly, that has underflow issues already, so I think you want > to basically make the check be > > if (rseq_cs->abort_ip >= TASK_SIZE) > return -EINVAL;
that works.
> > if (rseq_cs->start_ip >= rseq_cs->abort_ip) > return -EINVAL;
this one does not work. We need to ensure that abort_ip is not between [ start_ip, start_ip + post_commit_offset ]. The check you propose validates that start_ip is below abort_ip, which is bogus. For instance, abort_ip can very well be in a different section of the binary, at an address either below or above start_ip.
> > which takes care of checkint start_ip, and also the underflow for the > post_commit_offset check.
What underflow issues are you concerned with ?
> > If somebody is depending on negative offsets, then that > post_commit_offset logic is already wrong. > >> + usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32)); >> ret = get_user(sig, usig); > > That can underflow too, but I guess we can just rely on get_user() > getting it right.
Yes, get_user() should handle that one properly.
Thanks,
Mathieu
> > Linus
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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