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Message-ID: <45b3d69d-7356-2c28-e507-897889be564c@fb.com>
Date: Thu, 3 Dec 2020 21:27:04 -0800
From: Yonghong Song <yhs@...com>
To: Brendan Jackman <jackmanb@...gle.com>, <bpf@...r.kernel.org>
CC: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
KP Singh <kpsingh@...omium.org>,
Florent Revest <revest@...omium.org>,
<linux-kernel@...r.kernel.org>, Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH bpf-next v3 07/14] bpf: Add BPF_FETCH field / create
atomic_fetch_add instruction
On 12/3/20 8:02 AM, Brendan Jackman wrote:
> This value can be set in bpf_insn.imm, for BPF_ATOMIC instructions,
> in order to have the previous value of the atomically-modified memory
> location loaded into the src register after an atomic op is carried
> out.
>
> Suggested-by: Yonghong Song <yhs@...com>
> Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
> Change-Id: I649ad48edb565a32ccdf72924ffe96a8c8da57ad
> ---
> arch/x86/net/bpf_jit_comp.c | 4 ++++
> include/linux/filter.h | 9 +++++++++
> include/uapi/linux/bpf.h | 3 +++
> kernel/bpf/core.c | 13 +++++++++++++
> kernel/bpf/disasm.c | 7 +++++++
> kernel/bpf/verifier.c | 35 ++++++++++++++++++++++++----------
> tools/include/linux/filter.h | 10 ++++++++++
> tools/include/uapi/linux/bpf.h | 3 +++
> 8 files changed, 74 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 5e5a132b3d52..88cb09fa3bfb 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -827,6 +827,10 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
> /* lock *(u32/u64*)(dst_reg + off) <op>= src_reg */
> EMIT1(simple_alu_opcodes[atomic_op]);
> break;
> + case BPF_ADD | BPF_FETCH:
> + /* src_reg = atomic_fetch_add(*(dst_reg + off), src_reg); */
> + EMIT2(0x0F, 0xC1);
> + break;
> default:
> pr_err("bpf_jit: unknown atomic opcode %02x\n", atomic_op);
> return -EFAULT;
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index ce19988fb312..4e04d0fc454f 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -270,6 +270,15 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
> .imm = BPF_ADD })
> #define BPF_STX_XADD BPF_ATOMIC_ADD /* alias */
>
> +/* Atomic memory add with fetch, src_reg = atomic_fetch_add(*(dst_reg + off), src_reg); */
> +
> +#define BPF_ATOMIC_FETCH_ADD(SIZE, DST, SRC, OFF) \
> + ((struct bpf_insn) { \
> + .code = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC, \
> + .dst_reg = DST, \
> + .src_reg = SRC, \
> + .off = OFF, \
> + .imm = BPF_ADD | BPF_FETCH })
>
> /* Memory store, *(uint *) (dst_reg + off16) = imm32 */
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index d0adc48db43c..025e377e7229 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -44,6 +44,9 @@
> #define BPF_CALL 0x80 /* function call */
> #define BPF_EXIT 0x90 /* function return */
>
> +/* atomic op type fields (stored in immediate) */
> +#define BPF_FETCH 0x01 /* fetch previous value into src reg */
> +
> /* Register numbers */
> enum {
> BPF_REG_0 = 0,
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 3abc6b250b18..61e93eb7d363 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -1624,16 +1624,29 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
> /* lock xadd *(u32 *)(dst_reg + off16) += src_reg */
> atomic_add((u32) SRC, (atomic_t *)(unsigned long)
> (DST + insn->off));
> + break;
> + case BPF_ADD | BPF_FETCH:
> + SRC = (u32) atomic_fetch_add(
> + (u32) SRC,
> + (atomic_t *)(unsigned long) (DST + insn->off));
> + break;
> default:
> goto default_label;
> }
> CONT;
> +
> STX_ATOMIC_DW:
> switch (IMM) {
> case BPF_ADD:
> /* lock xadd *(u64 *)(dst_reg + off16) += src_reg */
> atomic64_add((u64) SRC, (atomic64_t *)(unsigned long)
> (DST + insn->off));
> + break;
> + case BPF_ADD | BPF_FETCH:
> + SRC = (u64) atomic64_fetch_add(
> + (u64) SRC,
> + (atomic64_t *)(s64) (DST + insn->off));
> + break;
> default:
> goto default_label;
> }
> diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c
> index 37c8d6e9b4cc..3ee2246a52ef 100644
> --- a/kernel/bpf/disasm.c
> +++ b/kernel/bpf/disasm.c
> @@ -160,6 +160,13 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
> bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
> insn->dst_reg, insn->off,
> insn->src_reg);
> + } else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
> + insn->imm == (BPF_ADD | BPF_FETCH)) {
> + verbose(cbs->private_data, "(%02x) r%d = atomic%s_fetch_add(*(%s *)(r%d %+d), r%d)\n",
We should not do dereference here (withough first *), right? since the
input is actually an address. something like below?
r2 = atomic[64]_fetch_add((u64/u32 *)(r3 +40), r2)
> + insn->code, insn->src_reg,
> + BPF_SIZE(insn->code) == BPF_DW ? "64" : "",
> + bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
> + insn->dst_reg, insn->off, insn->src_reg);
> } else {
> verbose(cbs->private_data, "BUG_%02x\n", insn->code);
> }
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index e8b41ccdfb90..a68adbcee370 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -3602,7 +3602,11 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
> {
> int err;
>
> - if (insn->imm != BPF_ADD) {
> + switch (insn->imm) {
> + case BPF_ADD:
> + case BPF_ADD | BPF_FETCH:
> + break;
> + default:
> verbose(env, "BPF_ATOMIC uses invalid atomic opcode %02x\n", insn->imm);
> return -EINVAL;
> }
> @@ -3631,7 +3635,7 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
> is_pkt_reg(env, insn->dst_reg) ||
> is_flow_key_reg(env, insn->dst_reg) ||
> is_sk_reg(env, insn->dst_reg)) {
> - verbose(env, "atomic stores into R%d %s is not allowed\n",
> + verbose(env, "BPF_ATOMIC stores into R%d %s is not allowed\n",
> insn->dst_reg,
> reg_type_str[reg_state(env, insn->dst_reg)->type]);
> return -EACCES;
> @@ -3644,8 +3648,20 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
> return err;
>
> /* check whether we can write into the same memory */
> - return check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
> - BPF_SIZE(insn->code), BPF_WRITE, -1, true);
> + err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
> + BPF_SIZE(insn->code), BPF_WRITE, -1, true);
> + if (err)
> + return err;
> +
> + if (!(insn->imm & BPF_FETCH))
> + return 0;
> +
> + /* check and record load of old value into src reg */
> + err = check_reg_arg(env, insn->src_reg, DST_OP);
> + if (err)
> + return err;
> +
> + return 0;
> }
>
> static int __check_stack_boundary(struct bpf_verifier_env *env, u32 regno,
> @@ -9501,12 +9517,6 @@ static int do_check(struct bpf_verifier_env *env)
> } else if (class == BPF_STX) {
> enum bpf_reg_type *prev_dst_type, dst_reg_type;
>
> - if (((BPF_MODE(insn->code) != BPF_MEM &&
> - BPF_MODE(insn->code) != BPF_ATOMIC) || insn->imm != 0)) {
> - verbose(env, "BPF_STX uses reserved fields\n");
> - return -EINVAL;
> - }
> -
> if (BPF_MODE(insn->code) == BPF_ATOMIC) {
> err = check_atomic(env, env->insn_idx, insn);
> if (err)
> @@ -9515,6 +9525,11 @@ static int do_check(struct bpf_verifier_env *env)
> continue;
> }
>
> + if (BPF_MODE(insn->code) != BPF_MEM || insn->imm != 0) {
> + verbose(env, "BPF_STX uses reserved fields\n");
> + return -EINVAL;
> + }
> +
> /* check src1 operand */
> err = check_reg_arg(env, insn->src_reg, SRC_OP);
> if (err)
> diff --git a/tools/include/linux/filter.h b/tools/include/linux/filter.h
> index 95ff51d97f25..ac7701678e1a 100644
> --- a/tools/include/linux/filter.h
> +++ b/tools/include/linux/filter.h
> @@ -180,6 +180,16 @@
> .imm = BPF_ADD })
> #define BPF_STX_XADD BPF_ATOMIC_ADD /* alias */
>
> +/* Atomic memory add with fetch, src_reg = atomic_fetch_add(*(dst_reg + off), src_reg); */
Maybe src_reg = atomic_fetch_add(dst_reg + off, src_reg)?
> +
> +#define BPF_ATOMIC_FETCH_ADD(SIZE, DST, SRC, OFF) \
> + ((struct bpf_insn) { \
> + .code = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC, \
> + .dst_reg = DST, \
> + .src_reg = SRC, \
> + .off = OFF, \
> + .imm = BPF_ADD | BPF_FETCH })
> +
> /* Memory store, *(uint *) (dst_reg + off16) = imm32 */
>
> #define BPF_ST_MEM(SIZE, DST, OFF, IMM) \
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index d0adc48db43c..025e377e7229 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -44,6 +44,9 @@
> #define BPF_CALL 0x80 /* function call */
> #define BPF_EXIT 0x90 /* function return */
>
> +/* atomic op type fields (stored in immediate) */
> +#define BPF_FETCH 0x01 /* fetch previous value into src reg */
> +
> /* Register numbers */
> enum {
> BPF_REG_0 = 0,
>
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