Messages in this thread |  | | From | Hao Luo <> | Date | Tue, 1 Sep 2020 12:47:02 -0700 | Subject | Re: [PATCH bpf-next v1 8/8] bpf/selftests: Test for bpf_per_cpu_ptr() |
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On Tue, Sep 1, 2020 at 11:12 AM Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote: > > On Thu, Aug 27, 2020 at 8:42 PM Hao Luo <haoluo@google.com> wrote: > > [...] > > > > > > > > -extern const struct rq runqueues __ksym; /* struct type global var. */ > > > > +extern const struct rq runqueues __ksym; /* struct type percpu var. */ > > > > extern const int bpf_prog_active __ksym; /* int type global var. */ > > > > +extern const unsigned long process_counts __ksym; /* int type percpu var. */ > > > > > > > > SEC("raw_tp/sys_enter") > > > > int handler(const void *ctx) > > > > { > > > > + struct rq *rq; > > > > + unsigned long *count; > > > > + > > > > out__runqueues = (__u64)&runqueues; > > > > out__bpf_prog_active = (__u64)&bpf_prog_active; > > > > > > > > + rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, 1); > > > > + if (rq) > > > > + out__rq_cpu = rq->cpu; > > > > > > this is awesome! > > > > > > Are there any per-cpu variables that are arrays? Would be nice to test > > > those too. > > > > > > > > > > There are currently per-cpu arrays, but not common. There is a > > 'pmc_prev_left' in arch/x86, I can add that in this test. > > arch-specific variables are bad, because selftests will be failing on > other architectures; let's not do this then. >
Yeah, no problem. Though not going to add this arch-specific variable in the posted patches, I tried array-typed ksyms locally in my test environment. It worked fine, except that the array size is not checked. For instance, if there is a percpu array in kernel as
DEFINE_PER_CPU(u32[64], foo);
we can declare a ksym of different size and it passes libbpf checks and kernel verification.
extern u32 foo[128] __ksyms;
It seems that bpf_core_types_are_compat() doesn't check nr_elem. But it seems the kernel verifier does check out-of-bounds accesses, so this may not be a real problem. Just want to list what I saw.
> > > > [...]
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