diff mbox series

[bpf-next,v5,06/11] bpf: Add BPF_FETCH field / create atomic_fetch_add instruction

Message ID 20201215121816.1048557-8-jackmanb@google.com (mailing list archive)
State Changes Requested
Delegated to: BPF
Headers show
Series Atomics for eBPF | expand

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netdev/fixes_present success Link
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netdev/tree_selection success Clearly marked for bpf-next
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netdev/source_inline success Was 0 now: 0
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netdev/module_param success Was 0 now: 0
netdev/build_32bit success Errors and warnings before: 15634 this patch: 15634
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/verify_fixes success Link
netdev/checkpatch warning CHECK: Lines should not end with a '(' CHECK: No space is necessary after a cast WARNING: line length of 109 exceeds 80 columns WARNING: line length of 81 exceeds 80 columns WARNING: line length of 83 exceeds 80 columns
netdev/build_allmodconfig_warn success Errors and warnings before: 15302 this patch: 15302
netdev/header_inline success Link
netdev/stable success Stable not CCed

Commit Message

Brendan Jackman Dec. 15, 2020, 12:18 p.m. UTC 
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@fb.com>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
---
 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   |  1 +
 tools/include/uapi/linux/bpf.h |  3 +++
 8 files changed, 56 insertions(+), 9 deletions(-)
diff mbox series

Patch

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 3463ac0c0259..c3e87a63e0b8 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_ATOMIC_OP(SIZE, OP, DST, SRC, OFF)			\
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 7bd3671bff20..760ae333a5ed 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..2b1d3fea03fc 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 *)(unsigned long) (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 48e398667a69..449b2da9b6db 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3608,7 +3608,11 @@  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;
 	}
@@ -3650,8 +3654,20 @@  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,
@@ -9528,12 +9544,6 @@  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)
@@ -9542,6 +9552,11 @@  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 e870c9039f0d..7211ce9fba53 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_ATOMIC_OP(SIZE, OP, DST, SRC, OFF)			\
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 7bd3671bff20..760ae333a5ed 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,