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SubjectRe: Re: [RFC v1 06/14] krsi: Implement eBPF operations, attachment and execution
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On 9/14/19 5:56 PM, Yonghong Song wrote:
>
>
> On 9/10/19 12:55 PM, KP Singh wrote:
>> From: KP Singh <kpsingh@google.com>
>>
>> A user space program can attach an eBPF program by:
>>
>> hook_fd = open("/sys/kernel/security/krsi/process_execution", O_RDWR)
>> prog_fd = bpf(BPF_PROG_LOAD, ...)
>> bpf(BPF_PROG_ATTACH, hook_fd, prog_fd)
>>
>> When such an attach call is received, the attachment logic looks up the
>> dentry and appends the program to the bpf_prog_array.
>>
>> The BPF programs are stored in a bpf_prog_array and writes to the array
>> are guarded by a mutex. The eBPF programs are executed as a part of the
>> LSM hook they are attached to. If any of the eBPF programs return
>> an error (-ENOPERM) the action represented by the hook is denied.
>>
>> Signed-off-by: KP Singh <kpsingh@google.com>
>> ---
>> include/linux/krsi.h | 18 ++++++
>> kernel/bpf/syscall.c | 3 +-
>> security/krsi/include/krsi_init.h | 51 +++++++++++++++
>> security/krsi/krsi.c | 13 +++-
>> security/krsi/krsi_fs.c | 28 ++++++++
>> security/krsi/ops.c | 102 ++++++++++++++++++++++++++++++
>> 6 files changed, 213 insertions(+), 2 deletions(-)
>> create mode 100644 include/linux/krsi.h
>>
[...]
>>
>> +static inline int krsi_run_progs(enum krsi_hook_type t, struct krsi_ctx *ctx)
>> +{
>> + struct bpf_prog_array_item *item;
>> + struct bpf_prog *prog;
>> + struct krsi_hook *h = &krsi_hooks_list[t];
>> + int ret, retval = 0;
>
> Reverse christmas tree style?
>
>> +
>> + preempt_disable();
>
> Do we need preempt_disable() here?

From the following patches, I see perf_event_output() helper
and per-cpu array usage. So, indeed preempt_disable() is needed.

>
>> + rcu_read_lock();
>> +
>> + item = rcu_dereference(h->progs)->items;
>> + while ((prog = READ_ONCE(item->prog))) {
>> + ret = BPF_PROG_RUN(prog, ctx);
>> + if (ret < 0) {
>> + retval = ret;
>> + goto out;
>> + }
>> + item++;
>> + }
>> +
>> +out:
>> + rcu_read_unlock();
>> + preempt_enable();
>> + return IS_ENABLED(CONFIG_SECURITY_KRSI_ENFORCE) ? retval : 0;
>> +}
>> +
[...]
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