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Subject[PATCH bpf-next v3 0/7] Introduce BPF_MODIFY_RET tracing progs
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From: KP Singh <kpsingh@google.com>

v2 -> v3:

* bpf_trampoline_update_progs -> bpf_trampoline_get_progs + const
qualification.
* Typos in commit messages.
* Added Andrii's Acks.

v1 -> v2:

* Adressed Andrii's feedback.
* Fixed a bug that Alexei noticed about nop generation.
* Rebase.

This was brought up in the KRSI v4 discussion and found to be useful
both for security and tracing programs.

https://lore.kernel.org/bpf/20200225193108.GB22391@chromium.org/

The modify_return programs are allowed for security hooks (with an
extra CAP_MAC_ADMIN check) and functions whitelisted for error
injection (ALLOW_ERROR_INJECTION).

The "security_" check is expected to be cleaned up with the KRSI patch
series.

Here is an example of how a fmod_ret program behaves:

int func_to_be_attached(int a, int b)
{ <--- do_fentry

do_fmod_ret:
<update ret by calling fmod_ret>
if (ret != 0)
goto do_fexit;

original_function:

<side_effects_happen_here>

} <--- do_fexit

ALLOW_ERROR_INJECTION(func_to_be_attached, ERRNO)

The fmod_ret program attached to this function can be defined as:

SEC("fmod_ret/func_to_be_attached")
int BPF_PROG(func_name, int a, int b, int ret)
{
// This will skip the original function logic.
return -1;
}

KP Singh (7):
bpf: Refactor trampoline update code
bpf: JIT helpers for fmod_ret progs
bpf: Introduce BPF_MODIFY_RETURN
bpf: Attachment verification for BPF_MODIFY_RETURN
tools/libbpf: Add support for BPF_MODIFY_RETURN
bpf: Add test ops for BPF_PROG_TYPE_TRACING
bpf: Add selftests for BPF_MODIFY_RETURN

arch/x86/net/bpf_jit_comp.c | 279 +++++++++++++-----
include/linux/bpf.h | 24 +-
include/uapi/linux/bpf.h | 1 +
kernel/bpf/bpf_struct_ops.c | 12 +-
kernel/bpf/btf.c | 27 +-
kernel/bpf/syscall.c | 1 +
kernel/bpf/trampoline.c | 65 ++--
kernel/bpf/verifier.c | 32 ++
kernel/trace/bpf_trace.c | 1 +
net/bpf/test_run.c | 57 +++-
tools/include/uapi/linux/bpf.h | 1 +
tools/lib/bpf/libbpf.c | 4 +
.../selftests/bpf/prog_tests/fentry_fexit.c | 12 +-
.../selftests/bpf/prog_tests/fentry_test.c | 14 +-
.../selftests/bpf/prog_tests/fexit_test.c | 69 ++---
.../selftests/bpf/prog_tests/modify_return.c | 65 ++++
.../selftests/bpf/progs/modify_return.c | 49 +++
17 files changed, 526 insertions(+), 187 deletions(-)
create mode 100644 tools/testing/selftests/bpf/prog_tests/modify_return.c
create mode 100644 tools/testing/selftests/bpf/progs/modify_return.c

--
2.20.1

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