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Merge branch 'Make 2-byte access to bpf_sk_lookup->remote_port endian-agnostic'

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Jakub Sitnicki says:

====================

This patch set is a result of a discussion we had around the RFC patchset from
Ilya [1]. The fix for the narrow loads from the RFC series is still relevant,
but this series does not depend on it. Nor is it required to unbreak sk_lookup
tests on BE, if this series gets applied.

To summarize the takeaways from [1]:

 1) we want to make 2-byte load from ctx->remote_port portable across LE and BE,
 2) we keep the 4-byte load from ctx->remote_port as it is today - result varies
    on endianess of the platform.

[1] https://lore.kernel.org/bpf/20220222182559.2865596-2-iii@linux.ibm.com/

v1 -> v2:
- Remove needless check that 4-byte load is from &ctx->remote_port offset
  (Martin)

[v1]: https://lore.kernel.org/bpf/20220317165826.1099418-1-jakub@cloudflare.com/
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Alexei Starovoitov 2022-03-20 18:59:00 -07:00
commit 46e9244b25
2 changed files with 27 additions and 6 deletions
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20
net/core/filter.c
View File

@ -10989,13 +10989,24 @@ static bool sk_lookup_is_valid_access(int off, int size,
case bpf_ctx_range(struct bpf_sk_lookup, local_ip4):
case bpf_ctx_range_till(struct bpf_sk_lookup, remote_ip6[0], remote_ip6[3]):
case bpf_ctx_range_till(struct bpf_sk_lookup, local_ip6[0], local_ip6[3]):
case offsetof(struct bpf_sk_lookup, remote_port) ...
offsetof(struct bpf_sk_lookup, local_ip4) - 1:
case bpf_ctx_range(struct bpf_sk_lookup, local_port):
case bpf_ctx_range(struct bpf_sk_lookup, ingress_ifindex):
bpf_ctx_record_field_size(info, sizeof(__u32));
return bpf_ctx_narrow_access_ok(off, size, sizeof(__u32));
case bpf_ctx_range(struct bpf_sk_lookup, remote_port):
/* Allow 4-byte access to 2-byte field for backward compatibility */
if (size == sizeof(__u32))
return true;
bpf_ctx_record_field_size(info, sizeof(__be16));
return bpf_ctx_narrow_access_ok(off, size, sizeof(__be16));
case offsetofend(struct bpf_sk_lookup, remote_port) ...
offsetof(struct bpf_sk_lookup, local_ip4) - 1:
/* Allow access to zero padding for backward compatibility */
bpf_ctx_record_field_size(info, sizeof(__u16));
return bpf_ctx_narrow_access_ok(off, size, sizeof(__u16));
default:
return false;
}
@ -11077,6 +11088,11 @@ static u32 sk_lookup_convert_ctx_access(enum bpf_access_type type,
sport, 2, target_size));
break;
case offsetofend(struct bpf_sk_lookup, remote_port):
*target_size = 2;
*insn++ = BPF_MOV32_IMM(si->dst_reg, 0);
break;
case offsetof(struct bpf_sk_lookup, local_port):
*insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->src_reg,
bpf_target_off(struct bpf_sk_lookup_kern,

13
tools/testing/selftests/bpf/progs/test_sk_lookup.c
View File

@ -413,15 +413,20 @@ int ctx_narrow_access(struct bpf_sk_lookup *ctx)
/* Narrow loads from remote_port field. Expect SRC_PORT. */
if (LSB(ctx->remote_port, 0) != ((SRC_PORT >> 0) & 0xff) ||
LSB(ctx->remote_port, 1) != ((SRC_PORT >> 8) & 0xff) ||
LSB(ctx->remote_port, 2) != 0 || LSB(ctx->remote_port, 3) != 0)
LSB(ctx->remote_port, 1) != ((SRC_PORT >> 8) & 0xff))
return SK_DROP;
if (LSW(ctx->remote_port, 0) != SRC_PORT)
return SK_DROP;
/* Load from remote_port field with zero padding (backward compatibility) */
/*
* NOTE: 4-byte load from bpf_sk_lookup at remote_port offset
* is quirky. It gets rewritten by the access converter to a
* 2-byte load for backward compatibility. Treating the load
* result as a be16 value makes the code portable across
* little- and big-endian platforms.
*/
val_u32 = *(__u32 *)&ctx->remote_port;
if (val_u32 != bpf_htonl(bpf_ntohs(SRC_PORT) << 16))
if (val_u32 != SRC_PORT)
return SK_DROP;
/* Narrow loads from local_port field. Expect DST_PORT. */