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Date: Sun, 30 Jun 2019 05:52:42 +0000
From: Yonghong Song <yhs@...com>
To: Stanislav Fomichev <sdf@...gle.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>
CC: "davem@...emloft.net" <davem@...emloft.net>,
"ast@...nel.org" <ast@...nel.org>,
"daniel@...earbox.net" <daniel@...earbox.net>,
"Andrii Nakryiko" <andriin@...com>,
kernel test robot <rong.a.chen@...el.com>
Subject: Re: [PATCH bpf-next 1/2] bpf: allow wide (u64) aligned stores for
some fields of bpf_sock_addr
On 6/28/19 4:10 PM, Stanislav Fomichev wrote:
> Since commit cd17d7770578 ("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@...com>
> Cc: Yonghong Song <yhs@...com>
> Fixes: cd17d7770578 ("bpf/tools: sync bpf.h")
> Reported-by: kernel test robot <rong.a.chen@...el.com>
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
The change looks good to me with the following nits:
1. could you add a cover letter for the patch set?
typically if the number of patches is more than one,
it would be a good practice with a cover letter.
See bpf_devel_QA.rst .
2. with this change, the comments in uapi bpf.h
are not accurate any more.
__u32 user_ip6[4]; /* Allows 1,2,4-byte read an 4-byte write.
* Stored in network byte order.
*/
__u32 msg_src_ip6[4]; /* Allows 1,2,4-byte read an 4-byte write.
* Stored in network byte order.
*/
now for stores, aligned 8-byte write is permitted.
could you update this as well?
From the typical usage pattern, I did not see a need
for 8-tye read of user_ip6 and msg_src_ip6 yet. So let
us just deal with write for now.
With the above two nits,
Acked-by: Yonghong Song <yhs@...com>
> ---
> include/linux/filter.h | 6 ++++++
> net/core/filter.c | 22 ++++++++++++++--------
> 2 files changed, 20 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 340f7d648974..3901007e36f1 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -746,6 +746,12 @@ 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)
> diff --git a/net/core/filter.c b/net/core/filter.c
> index dc8534be12fc..5d33f2146dab 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -6849,6 +6849,16 @@ 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;
> }
> @@ -7689,9 +7699,6 @@ 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
> @@ -7699,7 +7706,7 @@ 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) \
> @@ -7710,8 +7717,7 @@ 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); \
> @@ -7723,8 +7729,8 @@ 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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