Add tests to directly accesse sock_ops sk field. Then use it to
ensure a bad pointer access will fault if something goes wrong.
We do three tests:
The first test ensures when we read sock_ops sk pointer into the
same register that we don't fault as described earlier. Here r9
is chosen as the temp register. The xlated code is,
36: (7b) *(u64 *)(r1 +32) = r9
37: (61) r9 = *(u32 *)(r1 +28)
38: (15) if r9 == 0x0 goto pc+3
39: (79) r9 = *(u64 *)(r1 +32)
40: (79) r1 = *(u64 *)(r1 +0)
41: (05) goto pc+1
42: (79) r9 = *(u64 *)(r1 +32)
The second test ensures the temp register selection does not collide
with in-use register r9. Shown here r8 is chosen because r9 is the
sock_ops pointer. The xlated code is as follows,
46: (7b) *(u64 *)(r9 +32) = r8
47: (61) r8 = *(u32 *)(r9 +28)
48: (15) if r8 == 0x0 goto pc+3
49: (79) r8 = *(u64 *)(r9 +32)
50: (79) r9 = *(u64 *)(r9 +0)
51: (05) goto pc+1
52: (79) r8 = *(u64 *)(r9 +32)
And finally, ensure we didn't break the base case where dst_reg does
not equal the source register,
56: (61) r2 = *(u32 *)(r1 +28)
57: (15) if r2 == 0x0 goto pc+1
58: (79) r2 = *(u64 *)(r1 +0)
Notice it takes us an extra four instructions when src reg is the
same as dst reg. One to save the reg, two to restore depending on
the branch taken and a goto to jump over the second restore.
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/159718355325.4728.4163036953345999636.stgit@john-Precision-5820-Tower
==================
BPF Selftest Notes
==================
General instructions on running selftests can be found in
`Documentation/bpf/bpf_devel_QA.rst`_.
Additional information about selftest failures are
documented here.
bpf_iter test failures with clang/llvm 10.0.0
=============================================
With clang/llvm 10.0.0, the following two bpf_iter tests failed:
* ``bpf_iter/ipv6_route``
* ``bpf_iter/netlink``
The symptom for ``bpf_iter/ipv6_route`` looks like
.. code-block:: c
2: (79) r8 = *(u64 *)(r1 +8)
...
14: (bf) r2 = r8
15: (0f) r2 += r1
; BPF_SEQ_PRINTF(seq, "%pi6 %02x ", &rt->fib6_dst.addr, rt->fib6_dst.plen);
16: (7b) *(u64 *)(r8 +64) = r2
only read is supported
The symptom for ``bpf_iter/netlink`` looks like
.. code-block:: c
; struct netlink_sock *nlk = ctx->sk;
2: (79) r7 = *(u64 *)(r1 +8)
...
15: (bf) r2 = r7
16: (0f) r2 += r1
; BPF_SEQ_PRINTF(seq, "%pK %-3d ", s, s->sk_protocol);
17: (7b) *(u64 *)(r7 +0) = r2
only read is supported
This is due to a llvm BPF backend bug. The fix
https://reviews.llvm.org/D78466
has been pushed to llvm 10.x release branch and will be
available in 10.0.1. The fix is available in llvm 11.0.0 trunk.
9efa9e4997