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SubjectRe: [PATCH bpf-next v1 12/13] bpf: lsm: Add selftests for BPF_PROG_TYPE_LSM
On 23-Dez 22:49, Andrii Nakryiko wrote:
> On Fri, Dec 20, 2019 at 7:42 AM KP Singh <kpsingh@chromium.org> wrote:
> >
> > From: KP Singh <kpsingh@google.com>
> >
> > * Load a BPF program that audits mprotect calls
> > * Attach the program to the "file_mprotect" LSM hook
> > * Verify if the program is actually loading by reading
> > securityfs
> > * Initialize the perf events buffer and poll for audit events
> > * Do an mprotect on some memory allocated on the heap
> > * Verify if the audit event was received
> >
> > Signed-off-by: KP Singh <kpsingh@google.com>
> > ---
> > MAINTAINERS | 2 +
> > .../bpf/prog_tests/lsm_mprotect_audit.c | 129 ++++++++++++++++++
> > .../selftests/bpf/progs/lsm_mprotect_audit.c | 58 ++++++++
> > 3 files changed, 189 insertions(+)
> > create mode 100644 tools/testing/selftests/bpf/prog_tests/lsm_mprotect_audit.c
> > create mode 100644 tools/testing/selftests/bpf/progs/lsm_mprotect_audit.c
> >
>
> [...]
>
> > +/*
> > + * Define some of the structs used in the BPF program.
> > + * Only the field names and their sizes need to be the
> > + * same as the kernel type, the order is irrelevant.
> > + */
> > +struct mm_struct {
> > + unsigned long start_brk, brk, start_stack;
> > +};
> > +
> > +struct vm_area_struct {
> > + unsigned long start_brk, brk, start_stack;
> > + unsigned long vm_start, vm_end;
> > + struct mm_struct *vm_mm;
> > + unsigned long vm_flags;
> > +};
> > +
> > +BPF_TRACE_3("lsm/file_mprotect", mprotect_audit,
> > + struct vm_area_struct *, vma,
> > + unsigned long, reqprot, unsigned long, prot)
> > +{
> > + struct mprotect_audit_log audit_log = {};
> > + int is_heap = 0;
> > +
> > + __builtin_preserve_access_index(({
>
> you don't need __builtin_preserve_access_index, if you mark
> vm_area_struct and mm_struct with
> __attribute__((preserve_access_index)

Cool, updated!

>
> > + is_heap = (vma->vm_start >= vma->vm_mm->start_brk &&
> > + vma->vm_end <= vma->vm_mm->brk);
> > + }));
> > +
> > + audit_log.magic = MPROTECT_AUDIT_MAGIC;
> > + audit_log.is_heap = is_heap;
> > + bpf_lsm_event_output(&perf_buf_map, BPF_F_CURRENT_CPU, &audit_log,
> > + sizeof(audit_log));
>
> You test would be much simpler if you use global variables to pass
> data back to userspace, instead of using perf buffer.
>
> Also please see fentry_fexit.c test for example of using BPF skeleton
> to shorten and simpify userspace part of test.

Thanks for the skeleton work!

This makes using global variables easier and the tests are indeed much
simpler, I have updated it for the next revision.

One follow up question regarding global variables, let's say I have
the following global variable defined in the BPF program:

struct result_info {
__u32 count;
};

struct result_info result = {
.count = 0,
};

The defintion of result_info needs to be included before the .skel.h
as it's not automatically generated or maybe I am missing a
trick here?

For now, I have defined this in a header which gets included both in
the program and the test.

- KP

>
> > + return 0;
> > +}
> > --
> > 2.20.1
> >

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