[PATCH bpf-next v4 06/11] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction
From: Brendan Jackman
Date: Mon Dec 07 2020 - 11:10:16 EST
The BPF_FETCH field 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@xxxxxx>
Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
---
arch/x86/net/bpf_jit_comp.c | 4 ++++
include/linux/filter.h | 1 +
include/uapi/linux/bpf.h | 3 +++
kernel/bpf/core.c | 13 +++++++++++++
kernel/bpf/disasm.c | 7 +++++++
kernel/bpf/verifier.c | 33 ++++++++++++++++++++++++---------
tools/include/linux/filter.h | 11 +++++++++++
tools/include/uapi/linux/bpf.h | 3 +++
8 files changed, 66 insertions(+), 9 deletions(-)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index b1829a534da1..eea7d8b0bb12 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -811,6 +811,10 @@ 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 45be19408f68..b5258bca10d2 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -264,6 +264,7 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
* Atomic operations:
*
* BPF_ADD *(uint *) (dst_reg + off16) += src_reg
+ * BPF_ADD | BPF_FETCH src_reg = atomic_fetch_add(dst_reg + off16, src_reg);
*/
#define BPF_ATOMIC64(OP, DST, SRC, OFF) \
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 98161e2d389f..d5389119291e 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..d2e20f6d0516 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",
+ 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 745c53df0485..f8c4e809297d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3610,7 +3610,11 @@ 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;
}
@@ -3652,8 +3656,20 @@ 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,
@@ -9527,12 +9543,6 @@ 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)
@@ -9541,6 +9551,11 @@ 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 f345f12c1ff8..4e0100ba52c2 100644
--- a/tools/include/linux/filter.h
+++ b/tools/include/linux/filter.h
@@ -173,6 +173,7 @@
* Atomic operations:
*
* BPF_ADD *(uint *) (dst_reg + off16) += src_reg
+ * BPF_ADD | BPF_FETCH src_reg = atomic_fetch_add(dst_reg + off16, src_reg);
*/
#define BPF_ATOMIC64(OP, DST, SRC, OFF) \
@@ -201,6 +202,16 @@
.off = OFF, \
.imm = BPF_ADD })
+/* 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 */
#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 98161e2d389f..d5389119291e 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,
--
2.29.2.576.ga3fc446d84-goog