Commit 600c70ba authored by Stanislav Fomichev's avatar Stanislav Fomichev Committed by Daniel Borkmann
Browse files

bpf: allow wide (u64) aligned stores for some fields of bpf_sock_addr 



Since commit cd17d777 ("bpf/tools: sync bpf.h") clang decided
that it can do a single u64 store into user_ip6[2] instead of two
separate u32 ones:

 #  17: (18) r2 = 0x100000000000000
 #  ; ctx->user_ip6[2] = bpf_htonl(DST_REWRITE_IP6_2);
 #  19: (7b) *(u64 *)(r1 +16) = r2
 #  invalid bpf_context access off=16 size=8

>From the compiler point of view it does look like a correct thing
to do, so let's support it on the kernel side.

Credit to Andrii Nakryiko for a proper implementation of
bpf_ctx_wide_store_ok.

Cc: Andrii Nakryiko <andriin@fb.com>
Cc: Yonghong Song <yhs@fb.com>
Fixes: cd17d777 ("bpf/tools: sync bpf.h")
Reported-by: default avatarkernel test robot <rong.a.chen@intel.com>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Acked-by: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarStanislav Fomichev <sdf@google.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent d2850ce0

include/linux/filter.h

+6 −0
Original line number Diff line number Diff line
@@ -747,6 +747,12 @@ bpf_ctx_narrow_access_ok(u32 off, u32 size, u32 size_default) 
	return size <= size_default && (size & (size - 1)) == 0;

}



#define bpf_ctx_wide_store_ok(off, size, type, field)			\

	(size == sizeof(__u64) &&					\

	off >= offsetof(type, field) &&					\

	off + sizeof(__u64) <= offsetofend(type, field) &&		\

	off % sizeof(__u64) == 0)



#define bpf_classic_proglen(fprog) (fprog->len * sizeof(fprog->filter[0]))



static inline void bpf_prog_lock_ro(struct bpf_prog *fp)

include/uapi/linux/bpf.h

+3 −3
Original line number Diff line number Diff line
@@ -3247,7 +3247,7 @@ struct bpf_sock_addr { 
	__u32 user_ip4;		/* Allows 1,2,4-byte read and 4-byte write.

				 * Stored in network byte order.

				 */

	__u32 user_ip6[4];	/* Allows 1,2,4-byte read an 4-byte write.

	__u32 user_ip6[4];	/* Allows 1,2,4-byte read and 4,8-byte write.

				 * Stored in network byte order.

				 */

	__u32 user_port;	/* Allows 4-byte read and write.
@@ -3256,10 +3256,10 @@ struct bpf_sock_addr { 
	__u32 family;		/* Allows 4-byte read, but no write */

	__u32 type;		/* Allows 4-byte read, but no write */

	__u32 protocol;		/* Allows 4-byte read, but no write */

	__u32 msg_src_ip4;	/* Allows 1,2,4-byte read an 4-byte write.

	__u32 msg_src_ip4;	/* Allows 1,2,4-byte read and 4-byte write.

				 * Stored in network byte order.

				 */

	__u32 msg_src_ip6[4];	/* Allows 1,2,4-byte read an 4-byte write.

	__u32 msg_src_ip6[4];	/* Allows 1,2,4-byte read and 4,8-byte write.

				 * Stored in network byte order.

				 */

	__bpf_md_ptr(struct bpf_sock *, sk);

net/core/filter.c

+14 −8
Original line number Diff line number Diff line
@@ -6890,6 +6890,16 @@ static bool sock_addr_is_valid_access(int off, int size, 
			if (!bpf_ctx_narrow_access_ok(off, size, size_default))

				return false;

		} else {

			if (bpf_ctx_wide_store_ok(off, size,

						  struct bpf_sock_addr,

						  user_ip6))

				return true;



			if (bpf_ctx_wide_store_ok(off, size,

						  struct bpf_sock_addr,

						  msg_src_ip6))

				return true;



			if (size != size_default)

				return false;

		}
@@ -7730,9 +7740,6 @@ static u32 xdp_convert_ctx_access(enum bpf_access_type type, 
/* SOCK_ADDR_STORE_NESTED_FIELD_OFF() has semantic similar to

 * SOCK_ADDR_LOAD_NESTED_FIELD_SIZE_OFF() but for store operation.

 *

 * It doesn't support SIZE argument though since narrow stores are not

 * supported for now.

 *

 * In addition it uses Temporary Field TF (member of struct S) as the 3rd

 * "register" since two registers available in convert_ctx_access are not

 * enough: we can't override neither SRC, since it contains value to store, nor
@@ -7740,7 +7747,7 @@ static u32 xdp_convert_ctx_access(enum bpf_access_type type, 
 * instructions. But we need a temporary place to save pointer to nested

 * structure whose field we want to store to.

 */

#define SOCK_ADDR_STORE_NESTED_FIELD_OFF(S, NS, F, NF, OFF, TF)		       \

#define SOCK_ADDR_STORE_NESTED_FIELD_OFF(S, NS, F, NF, SIZE, OFF, TF)	       \

	do {								       \

		int tmp_reg = BPF_REG_9;				       \

		if (si->src_reg == tmp_reg || si->dst_reg == tmp_reg)	       \
@@ -7751,8 +7758,7 @@ static u32 xdp_convert_ctx_access(enum bpf_access_type type, 
				      offsetof(S, TF));			       \

		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(S, F), tmp_reg,	       \

				      si->dst_reg, offsetof(S, F));	       \

		*insn++ = BPF_STX_MEM(					       \

			BPF_FIELD_SIZEOF(NS, NF), tmp_reg, si->src_reg,	       \

		*insn++ = BPF_STX_MEM(SIZE, tmp_reg, si->src_reg,	       \

			bpf_target_off(NS, NF, FIELD_SIZEOF(NS, NF),	       \

				       target_size)			       \

				+ OFF);					       \
@@ -7764,8 +7770,8 @@ static u32 xdp_convert_ctx_access(enum bpf_access_type type, 
						      TF)		       \

	do {								       \

		if (type == BPF_WRITE) {				       \

			SOCK_ADDR_STORE_NESTED_FIELD_OFF(S, NS, F, NF, OFF,    \

							 TF);		       \

			SOCK_ADDR_STORE_NESTED_FIELD_OFF(S, NS, F, NF, SIZE,   \

							 OFF, TF);	       \

		} else {						       \

			SOCK_ADDR_LOAD_NESTED_FIELD_SIZE_OFF(		       \

				S, NS, F, NF, SIZE, OFF);  \

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