Messages in this thread | | | Date | Mon, 2 Jul 2018 18:16:45 -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 6:08 PM, Linus Torvalds torvalds@linux-foundation.org wrote:
> On Mon, Jul 2, 2018 at 3:03 PM Mathieu Desnoyers > <mathieu.desnoyers@efficios.com> wrote: >> >> if (__get_user(ptr, &t->rseq->rseq_cs)) >> return -EINVAL; >> if (check_rseq_cs_padding(t)) >> return -EINVAL; > > Small nit. > > I think the _actual_ user access faults should return -EFAULT, and > then the *validation* checks should return -EINVAL. > > So when the "copy_from_user()" fails, that's -EFAULT, but when you > have (rseq_cs->start_ip >= TASK_SIZE), that's -EINVAL.
Fair enough.
> > That said, nothing actually cares or exposes the error number, I > think. Afaik, all the callers just check "did it work" or not.
Indeed, it's a static function and callers just check for zero/nonzero.
> > So this is more a "let's be consistent" than anything that matters.
Allright, here is the function updated accordingly:
static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs) { struct rseq_cs __user *urseq_cs; unsigned long ptr; u32 __user *usig; u32 sig; int ret;
ret = __get_user(ptr, &t->rseq->rseq_cs); if (ret) return ret; if (check_rseq_cs_padding(t)) return -EINVAL; if (!ptr) { memset(rseq_cs, 0, sizeof(*rseq_cs)); return 0; } urseq_cs = (struct rseq_cs __user *)ptr; if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs))) return -EFAULT;
if (rseq_cs->start_ip >= TASK_SIZE || rseq_cs->start_ip + rseq_cs->post_commit_offset >= TASK_SIZE || rseq_cs->abort_ip >= TASK_SIZE || rseq_cs->version > 0) return -EINVAL; /* Check for overflow. */ if (rseq_cs->start_ip + rseq_cs->post_commit_offset < rseq_cs->start_ip) return -EINVAL; /* 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;
usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32)); ret = get_user(sig, usig); if (ret) return ret;
if (current->rseq_sig != sig) { printk_ratelimited(KERN_WARNING "Possible attack attempt. Unexpected rseq signature 0x%x, expecting 0x%x (pid=%d, addr=%p).\n", sig, current->rseq_sig, current->pid, usig); return -EINVAL; } return 0; }
Thanks for the feedback!
Mathieu
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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