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Message-ID: <4ba606ff-34ee-6cb3-40e4-2d004b8689dd@iogearbox.net> Date: Wed, 23 Jan 2019 12:55:00 +0100 From: Daniel Borkmann <daniel@...earbox.net> To: Martin Lau <kafai@...com>, Eric Dumazet <edumazet@...gle.com> Cc: Alexei Starovoitov <ast@...nel.org>, netdev <netdev@...r.kernel.org>, Eric Dumazet <eric.dumazet@...il.com>, Eddie Hao <eddieh@...gle.com>, Vlad Dumitrescu <vladum@...gle.com>, Xiaotian Pei <xiaotian@...gle.com>, Yuchung Cheng <ycheng@...gle.com> Subject: Re: [PATCH v2 bpf-next] bpf: allow BPF programs access skb_shared_info->gso_segs field On 01/18/2019 07:42 PM, Martin Lau wrote: > On Thu, Jan 17, 2019 at 03:31:57PM -0800, Eric Dumazet wrote: >> This adds the ability to read gso_segs from a BPF program. >> >> v2: refined Eddie Hao patch to address Alexei feedback. >> >> Signed-off-by: Eric Dumazet <edumazet@...gle.com> >> Cc: Eddie Hao <eddieh@...gle.com> >> Cc: Vlad Dumitrescu <vladum@...gle.com> >> Cc: Xiaotian Pei <xiaotian@...gle.com> >> Cc: Yuchung Cheng <ycheng@...gle.com> >> --- >> include/uapi/linux/bpf.h | 1 + >> net/core/filter.c | 21 ++++++++++++ >> tools/include/uapi/linux/bpf.h | 1 + >> tools/testing/selftests/bpf/test_verifier.c | 36 +++++++++++++++++++++ >> 4 files changed, 59 insertions(+) >> >> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h >> index 91c43884f295f60a85268ddf0020bf8aa47f8329..2940a9854f6d8e493518ca894e0c9c630ae4ab7a 100644 >> --- a/include/uapi/linux/bpf.h >> +++ b/include/uapi/linux/bpf.h >> @@ -2540,6 +2540,7 @@ struct __sk_buff { >> __bpf_md_ptr(struct bpf_flow_keys *, flow_keys); >> __u64 tstamp; >> __u32 wire_len; >> + __u32 gso_segs; >> }; >> >> struct bpf_tunnel_key { >> diff --git a/net/core/filter.c b/net/core/filter.c >> index 2b3b436ef5457bf44c99780d6dec0b5f403f005c..a6ff5d9a04cf06926ee75cbc523456d12baf25ae 100644 >> --- a/net/core/filter.c >> +++ b/net/core/filter.c >> @@ -6700,6 +6700,27 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type, >> target_size)); >> break; >> >> + case offsetof(struct __sk_buff, gso_segs): >> + /* si->dst_reg = skb_shinfo(SKB); */ >> +#ifdef NET_SKBUFF_DATA_USES_OFFSET >> + *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, head), >> + si->dst_reg, si->src_reg, >> + offsetof(struct sk_buff, head)); >> + *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, end), >> + BPF_REG_TMP, si->src_reg, >> + offsetof(struct sk_buff, end)); > I am not sure BPF_REG_TMP can be used for non-classic BPF. > The earlier insn could be using BPF_REG_TMP (which is BPF_REG_2) and > R2 would become loss after this BPF_LDX_MEM. Yes, this will indeed corrupt R2 register. BPF_REG_TMP can only be used for reg mapping out of classic BPF. > Daniel, can BPF_REG_AX be used here as a tmp? BPF_REG_AX would work in this case, yes. Neither of the above insns are used in blinding nor would they collide with current verifier rewrites. >> + *insn++ = BPF_ALU64_REG(BPF_ADD, si->dst_reg, BPF_REG_TMP); >> +#else >> + *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, end), >> + si->dst_reg, si->src_reg, >> + offsetof(struct sk_buff, end)); >> +#endif >> + *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct skb_shared_info, gso_segs), >> + si->dst_reg, si->dst_reg, >> + bpf_target_off(struct skb_shared_info, >> + gso_segs, 2, >> + target_size)); >> + break; >> case offsetof(struct __sk_buff, wire_len): >> BUILD_BUG_ON(FIELD_SIZEOF(struct qdisc_skb_cb, pkt_len) != 4); >> >> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h >> index 91c43884f295f60a85268ddf0020bf8aa47f8329..2940a9854f6d8e493518ca894e0c9c630ae4ab7a 100644 >> --- a/tools/include/uapi/linux/bpf.h >> +++ b/tools/include/uapi/linux/bpf.h >> @@ -2540,6 +2540,7 @@ struct __sk_buff { >> __bpf_md_ptr(struct bpf_flow_keys *, flow_keys); >> __u64 tstamp; >> __u32 wire_len; >> + __u32 gso_segs; >> }; >> >> struct bpf_tunnel_key { >> diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c >> index 2fd90d4568926d13542783c870507d43a6d6bb64..2c46531044bdf9ec1e4fa47e2c94c9edb0ac3d08 100644 >> --- a/tools/testing/selftests/bpf/test_verifier.c >> +++ b/tools/testing/selftests/bpf/test_verifier.c >> @@ -5663,6 +5663,42 @@ static struct bpf_test tests[] = { >> .result = ACCEPT, >> .prog_type = BPF_PROG_TYPE_CGROUP_SKB, >> }, >> + { >> + "read gso_segs from CGROUP_SKB", >> + .insns = { >> + BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1, >> + offsetof(struct __sk_buff, gso_segs)), >> + BPF_MOV64_IMM(BPF_REG_0, 0), >> + BPF_EXIT_INSN(), >> + }, >> + .result = ACCEPT, >> + .prog_type = BPF_PROG_TYPE_CGROUP_SKB, >> + }, >> + { >> + "write gso_segs from CGROUP_SKB", >> + .insns = { >> + BPF_MOV64_IMM(BPF_REG_0, 0), >> + BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0, >> + offsetof(struct __sk_buff, gso_segs)), >> + BPF_MOV64_IMM(BPF_REG_0, 0), >> + BPF_EXIT_INSN(), >> + }, >> + .result = REJECT, >> + .result_unpriv = REJECT, >> + .errstr = "invalid bpf_context access off=164 size=4", >> + .prog_type = BPF_PROG_TYPE_CGROUP_SKB, >> + }, >> + { >> + "read gso_segs from CLS", >> + .insns = { >> + BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1, >> + offsetof(struct __sk_buff, gso_segs)), >> + BPF_MOV64_IMM(BPF_REG_0, 0), >> + BPF_EXIT_INSN(), >> + }, >> + .result = ACCEPT, >> + .prog_type = BPF_PROG_TYPE_SCHED_CLS, >> + }, >> { >> "multiple registers share map_lookup_elem result", >> .insns = { >> -- >> 2.20.1.321.g9e740568ce-goog >>
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