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bpf: Add write access to tcp_sock and sock fields

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This patch adds a macro, SOCK_OPS_SET_FIELD, for writing to
struct tcp_sock or struct sock fields. This required adding a new
field "temp" to struct bpf_sock_ops_kern for temporary storage that
is used by sock_ops_convert_ctx_access. It is used to store and recover
the contents of a register, so the register can be used to store the
address of the sk. Since we cannot overwrite the dst_reg because it
contains the pointer to ctx, nor the src_reg since it contains the value
we want to store, we need an extra register to contain the address
of the sk.

Also adds the macro SOCK_OPS_GET_OR_SET_FIELD that calls one of the
GET or SET macros depending on the value of the TYPE field.

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Lawrence Brakmo 2018-01-25 16:14:08 -08:00 committed by Alexei Starovoitov
parent 34d367c592
commit b73042b8a2
3 changed files with 58 additions and 1 deletions
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9
include/linux/filter.h
View File

@ -1007,6 +1007,15 @@ struct bpf_sock_ops_kern {
u32 replylong[4];
};
u32 is_fullsock;
u64 temp; /* temp and everything after is not
* initialized to 0 before calling
* the BPF program. New fields that
* should be initialized to 0 should
* be inserted before temp.
* temp is scratch storage used by
* sock_ops_convert_ctx_access
* as temporary storage of a register.
*/
};
#endif /* __LINUX_FILTER_H__ */

2
include/net/tcp.h
View File

@ -2011,7 +2011,7 @@ static inline int tcp_call_bpf(struct sock *sk, int op)
struct bpf_sock_ops_kern sock_ops;
int ret;
memset(&sock_ops, 0, sizeof(sock_ops));
memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
if (sk_fullsock(sk)) {
sock_ops.is_fullsock = 1;
sock_owned_by_me(sk);

48
net/core/filter.c
View File

@ -4491,6 +4491,54 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
offsetof(OBJ, OBJ_FIELD)); \
} while (0)
/* Helper macro for adding write access to tcp_sock or sock fields.
* The macro is called with two registers, dst_reg which contains a pointer
* to ctx (context) and src_reg which contains the value that should be
* stored. However, we need an additional register since we cannot overwrite
* dst_reg because it may be used later in the program.
* Instead we "borrow" one of the other register. We first save its value
* into a new (temp) field in bpf_sock_ops_kern, use it, and then restore
* it at the end of the macro.
*/
#define SOCK_OPS_SET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ) \
do { \
int reg = BPF_REG_9; \
BUILD_BUG_ON(FIELD_SIZEOF(OBJ, OBJ_FIELD) > \
FIELD_SIZEOF(struct bpf_sock_ops, BPF_FIELD)); \
if (si->dst_reg == reg || si->src_reg == reg) \
reg--; \
if (si->dst_reg == reg || si->src_reg == reg) \
reg--; \
*insn++ = BPF_STX_MEM(BPF_DW, si->dst_reg, reg, \
offsetof(struct bpf_sock_ops_kern, \
temp)); \
*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF( \
struct bpf_sock_ops_kern, \
is_fullsock), \
reg, si->dst_reg, \
offsetof(struct bpf_sock_ops_kern, \
is_fullsock)); \
*insn++ = BPF_JMP_IMM(BPF_JEQ, reg, 0, 2); \
*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF( \
struct bpf_sock_ops_kern, sk),\
reg, si->dst_reg, \
offsetof(struct bpf_sock_ops_kern, sk));\
*insn++ = BPF_STX_MEM(BPF_FIELD_SIZEOF(OBJ, OBJ_FIELD), \
reg, si->src_reg, \
offsetof(OBJ, OBJ_FIELD)); \
*insn++ = BPF_LDX_MEM(BPF_DW, reg, si->dst_reg, \
offsetof(struct bpf_sock_ops_kern, \
temp)); \
} while (0)
#define SOCK_OPS_GET_OR_SET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ, TYPE) \
do { \
if (TYPE == BPF_WRITE) \
SOCK_OPS_SET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ); \
else \
SOCK_OPS_GET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ); \
} while (0)
case offsetof(struct bpf_sock_ops, snd_cwnd):
SOCK_OPS_GET_FIELD(snd_cwnd, snd_cwnd, struct tcp_sock);
break;