lkml.org 
[lkml]   [2020]   [Jan]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v2 bpf-next 1/3] bpf: Add bpf_perf_prog_read_branches() helper
From
Date
On 1/23/20 11:30 PM, Daniel Xu wrote:
> On Thu Jan 23, 2020 at 11:23 PM, Daniel Borkmann wrote:
> [...]
>>
>> Yes, so we've been following this practice for all the BPF helpers no
>> matter
>> which program type. Though for tracing it may be up to debate whether it
>> makes
>> still sense given there's nothing to be leaked here since you can read
>> this data
>> anyway via probe read if you'd wanted to. So we might as well get rid of
>> the
>> clearing for all tracing helpers.
>
> Right, that makes sense. Do you want me to leave it in for this patchset
> and then remove all of them in a followup patchset?

Lets leave it in and in a different set, we can clean this up for all tracing
related helpers at once.

>> Different question related to your set. It looks like br_stack is only
>> available
>> on x86, is that correct? For other archs this will always bail out on
>> !br_stack
>> test. Perhaps we should document this fact so users are not surprised
>> why their
>> prog using this helper is not working on !x86. Wdyt?
>
> I think perf_event_open() should fail on !x86 if a user tries to configure
> it with branch stack collection. So there would not be the opportunity for
> the bpf prog to be attached and run. I haven't tested this, though. I'll
> look through the code / install a VM and test it.

As far as I can see the prog would still be attachable and runnable, just that
the helper always will return -EINVAL on these archs. Maybe error code should be
changed into -ENOENT to avoid confusion wrt whether user provided some invalid
input args. Should this actually bail out with -EINVAL if size is not a multiple
of sizeof(struct perf_branch_entry) as otherwise we'd end up copying half broken
branch entry information?

Thanks,
Daniel

\
 
 \ /
  Last update: 2020-01-23 23:45    [W:0.200 / U:0.052 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site