Re: [PATCH bpf-next v1 5/8] selftests/bpf: Add dynptr pruning tests

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: bpf@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <martin.lau@kernel.org>,
	Joanne Koong <joannelkoong@gmail.com>,
	David Vernet <void@manifault.com>,
	Eduard Zingerman <eddyz87@gmail.com>
Subject: Re: [PATCH bpf-next v1 5/8] selftests/bpf: Add dynptr pruning tests
Date: Wed, 4 Jan 2023 14:49:30 -0800	[thread overview]
Message-ID: <CAEf4Bzac9u4VDMVkuWutY5cGUMpRoxvpszy_gi6OZyXXP=Sp7Q@mail.gmail.com> (raw)
In-Reply-To: <20230101083403.332783-6-memxor@gmail.com>

On Sun, Jan 1, 2023 at 12:34 AM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> Add verifier tests that verify the new pruning behavior for STACK_DYNPTR
> slots, and ensure that state equivalence takes into account changes to
> the old and current verifier state correctly.
>
> Without the prior fixes, both of these bugs trigger with unprivileged
> BPF mode.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
>  tools/testing/selftests/bpf/verifier/dynptr.c | 90 +++++++++++++++++++
>  1 file changed, 90 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/verifier/dynptr.c
>
> diff --git a/tools/testing/selftests/bpf/verifier/dynptr.c b/tools/testing/selftests/bpf/verifier/dynptr.c
> new file mode 100644
> index 000000000000..798f4f7e0c57
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/verifier/dynptr.c
> @@ -0,0 +1,90 @@
> +{
> +       "dynptr: rewrite dynptr slot",
> +        .insns = {
> +        BPF_MOV64_IMM(BPF_REG_0, 0),
> +        BPF_LD_MAP_FD(BPF_REG_6, 0),
> +        BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
> +        BPF_MOV64_IMM(BPF_REG_2, 8),
> +        BPF_MOV64_IMM(BPF_REG_3, 0),
> +        BPF_MOV64_REG(BPF_REG_4, BPF_REG_10),
> +        BPF_ALU64_IMM(BPF_ADD, BPF_REG_4, -16),
> +        BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_ringbuf_reserve_dynptr),
> +        BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 1),
> +        BPF_JMP_IMM(BPF_JA, 0, 0, 1),
> +        BPF_ST_MEM(BPF_DW, BPF_REG_10, -16, 0xeB9F),
> +        BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
> +        BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -16),
> +        BPF_MOV64_IMM(BPF_REG_2, 0),
> +        BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_ringbuf_discard_dynptr),
> +        BPF_MOV64_IMM(BPF_REG_0, 0),
> +        BPF_EXIT_INSN(),
> +        },
> +       .fixup_map_ringbuf = { 1 },
> +       .result_unpriv = REJECT,
> +       .errstr_unpriv = "unknown func bpf_ringbuf_reserve_dynptr#198",
> +       .result = REJECT,
> +       .errstr = "arg 1 is an unacquired reference",
> +},
> +{
> +       "dynptr: type confusion",
> +       .insns = {
> +       BPF_MOV64_IMM(BPF_REG_0, 0),
> +       BPF_LD_MAP_FD(BPF_REG_6, 0),
> +       BPF_LD_MAP_FD(BPF_REG_7, 0),
> +       BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
> +       BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
> +       BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> +       BPF_ST_MEM(BPF_DW, BPF_REG_2, 0, 0),
> +       BPF_MOV64_REG(BPF_REG_3, BPF_REG_10),
> +       BPF_ALU64_IMM(BPF_ADD, BPF_REG_3, -24),
> +       BPF_ST_MEM(BPF_DW, BPF_REG_10, -16, 0xeB9FeB9F),
> +       BPF_ST_MEM(BPF_DW, BPF_REG_10, -24, 0xeB9FeB9F),
> +       BPF_MOV64_IMM(BPF_REG_4, 0),
> +       BPF_MOV64_REG(BPF_REG_8, BPF_REG_2),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_update_elem),
> +       BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
> +       BPF_MOV64_REG(BPF_REG_2, BPF_REG_8),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_map_lookup_elem),
> +       BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),
> +       BPF_EXIT_INSN(),
> +       BPF_MOV64_REG(BPF_REG_8, BPF_REG_0),
> +       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
> +       BPF_MOV64_IMM(BPF_REG_2, 8),
> +       BPF_MOV64_IMM(BPF_REG_3, 0),
> +       BPF_MOV64_REG(BPF_REG_4, BPF_REG_10),
> +       BPF_ALU64_IMM(BPF_ADD, BPF_REG_4, -16),
> +       BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, 0),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_ringbuf_reserve_dynptr),
> +       BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 8),
> +       /* pad with insns to trigger add_new_state heuristic for straight line path */
> +       BPF_MOV64_REG(BPF_REG_8, BPF_REG_8),
> +       BPF_MOV64_REG(BPF_REG_8, BPF_REG_8),
> +       BPF_MOV64_REG(BPF_REG_8, BPF_REG_8),
> +       BPF_MOV64_REG(BPF_REG_8, BPF_REG_8),
> +       BPF_MOV64_REG(BPF_REG_8, BPF_REG_8),
> +       BPF_MOV64_REG(BPF_REG_8, BPF_REG_8),
> +       BPF_MOV64_REG(BPF_REG_8, BPF_REG_8),
> +       BPF_JMP_IMM(BPF_JA, 0, 0, 9),
> +       BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
> +       BPF_ST_MEM(BPF_DW, BPF_REG_10, -16, 0),
> +       BPF_MOV64_REG(BPF_REG_1, BPF_REG_8),
> +       BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, 8),
> +       BPF_MOV64_IMM(BPF_REG_2, 0),
> +       BPF_MOV64_IMM(BPF_REG_3, 0),
> +       BPF_MOV64_REG(BPF_REG_4, BPF_REG_10),
> +       BPF_ALU64_IMM(BPF_ADD, BPF_REG_4, -16),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_dynptr_from_mem),
> +       BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
> +       BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -16),
> +       BPF_MOV64_IMM(BPF_REG_2, 0),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_ringbuf_discard_dynptr),
> +       BPF_MOV64_IMM(BPF_REG_0, 0),
> +       BPF_EXIT_INSN(),
> +       },
> +       .fixup_map_hash_16b = { 1 },
> +       .fixup_map_ringbuf = { 3 },
> +       .result_unpriv = REJECT,
> +       .errstr_unpriv = "unknown func bpf_ringbuf_reserve_dynptr#198",
> +       .result = REJECT,
> +       .errstr = "arg 1 is an unacquired reference",
> +},

have you tried to write these tests as embedded assembly in .bpf.c,
using __attribute__((naked)) and __failure and __msg("")
infrastructure? Eduard is working towards converting test_verifier's
test to this __naked + embed asm approach, so we might want to start
adding new tests in such form anyways? And they will be way more
readable. Defining and passing ringbuf map in C is also much more
obvious and easy.

> --
> 2.39.0
>