On 7/1/20 1:41 AM, Alexei Starovoitov wrote:
On Wed, Jul 01, 2020 at 01:26:44AM +0200, Daniel Borkmann wrote:
On 6/30/20 6:33 AM, Alexei Starovoitov wrote:
[...]
+/* list of non-sleepable kernel functions that are otherwise
+ * available to attach by bpf_lsm or fmod_ret progs.
+ */
+static int check_sleepable_blacklist(unsigned long addr)
+{
+#ifdef CONFIG_BPF_LSM
+ if (addr == (long)bpf_lsm_task_free)
+ return -EINVAL;
+#endif
+#ifdef CONFIG_SECURITY
+ if (addr == (long)security_task_free)
+ return -EINVAL;
+#endif
+ return 0;
+}
Would be nice to have some sort of generic function annotation to describe
that code cannot sleep inside of it, and then filter based on that. Anyway,
is above from manual code inspection?
yep. all manual. I don't think there is a way to automate it.
At least I cannot think of one.
Automation might be hard, but maybe semi-automate: we have a cant_migrate()
assertion in __BPF_PROG_RUN() which asserts on cant_sleep() PREEMPT_RT kernels
at least. We originally just has the cant_sleep() there before 37e1d9202225
("bpf: Replace cant_sleep() with cant_migrate()"). So perhaps one way to catch
bugs for sleepable progs is to add a __might_sleep() into __bpf_prog_enter_sleepable()
in order to trigger the assertion generally for DEBUG_ATOMIC_SLEEP configured
kernels when we're in non-sleepable sections? Still not perfect since the code
needs to be exercised first but better than nothing at all.
What about others like security_sock_rcv_skb() for example which could be
bh_lock_sock()'ed (or, generally hooks running in softirq context)?
ahh. it's in running in bh at that point? then it should be added to blacklist.
Yep.
Thanks,
Daniel
