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Message-Id: <20201215121816.1048557-11-jackmanb@google.com>
Date: Tue, 15 Dec 2020 12:18:14 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: bpf@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii.nakryiko@...il.com>,
KP Singh <kpsingh@...omium.org>,
Florent Revest <revest@...omium.org>,
linux-kernel@...r.kernel.org, Brendan Jackman <jackmanb@...gle.com>
Subject: [PATCH bpf-next v5 09/11] bpf: Add bitwise atomic instructions
This adds instructions for
atomic[64]_[fetch_]and
atomic[64]_[fetch_]or
atomic[64]_[fetch_]xor
All these operations are isomorphic enough to implement with the same
verifier, interpreter, and x86 JIT code, hence being a single commit.
The main interesting thing here is that x86 doesn't directly support
the fetch_ version these operations, so we need to generate a CMPXCHG
loop in the JIT. This requires the use of two temporary registers,
IIUC it's safe to use BPF_REG_AX and x86's AUX_REG for this purpose.
Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
---
arch/x86/net/bpf_jit_comp.c | 50 +++++++++++++++++++++++++++++++++++-
include/linux/filter.h | 6 +++++
kernel/bpf/core.c | 3 +++
kernel/bpf/disasm.c | 21 ++++++++++++---
kernel/bpf/verifier.c | 6 +++++
tools/include/linux/filter.h | 6 +++++
6 files changed, 87 insertions(+), 5 deletions(-)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 308241187582..1d4d50199293 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -808,6 +808,10 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
/* emit opcode */
switch (atomic_op) {
case BPF_ADD:
+ case BPF_SUB:
+ case BPF_AND:
+ case BPF_OR:
+ case BPF_XOR:
/* lock *(u32/u64*)(dst_reg + off) <op>= src_reg */
EMIT1(simple_alu_opcodes[atomic_op]);
break;
@@ -1292,8 +1296,52 @@ st: if (is_imm8(insn->off))
case BPF_STX | BPF_ATOMIC | BPF_W:
case BPF_STX | BPF_ATOMIC | BPF_DW:
+ if (insn->imm == (BPF_AND | BPF_FETCH) ||
+ insn->imm == (BPF_OR | BPF_FETCH) ||
+ insn->imm == (BPF_XOR | BPF_FETCH)) {
+ u8 *branch_target;
+ bool is64 = BPF_SIZE(insn->code) == BPF_DW;
+
+ /*
+ * Can't be implemented with a single x86 insn.
+ * Need to do a CMPXCHG loop.
+ */
+
+ /* Will need RAX as a CMPXCHG operand so save R0 */
+ emit_mov_reg(&prog, true, BPF_REG_AX, BPF_REG_0);
+ branch_target = prog;
+ /* Load old value */
+ emit_ldx(&prog, BPF_SIZE(insn->code),
+ BPF_REG_0, dst_reg, insn->off);
+ /*
+ * Perform the (commutative) operation locally,
+ * put the result in the AUX_REG.
+ */
+ emit_mov_reg(&prog, is64, AUX_REG, BPF_REG_0);
+ maybe_emit_mod(&prog, AUX_REG, src_reg, is64);
+ EMIT2(simple_alu_opcodes[BPF_OP(insn->imm)],
+ add_2reg(0xC0, AUX_REG, src_reg));
+ /* Attempt to swap in new value */
+ err = emit_atomic(&prog, BPF_CMPXCHG,
+ dst_reg, AUX_REG, insn->off,
+ BPF_SIZE(insn->code));
+ if (WARN_ON(err))
+ return err;
+ /*
+ * ZF tells us whether we won the race. If it's
+ * cleared we need to try again.
+ */
+ EMIT2(X86_JNE, -(prog - branch_target) - 2);
+ /* Return the pre-modification value */
+ emit_mov_reg(&prog, is64, src_reg, BPF_REG_0);
+ /* Restore R0 after clobbering RAX */
+ emit_mov_reg(&prog, true, BPF_REG_0, BPF_REG_AX);
+ break;
+
+ }
+
err = emit_atomic(&prog, insn->imm, dst_reg, src_reg,
- insn->off, BPF_SIZE(insn->code));
+ insn->off, BPF_SIZE(insn->code));
if (err)
return err;
break;
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 16e0ba5e8937..a0913e670a74 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -264,7 +264,13 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
* Atomic operations:
*
* BPF_ADD *(uint *) (dst_reg + off16) += src_reg
+ * BPF_AND *(uint *) (dst_reg + off16) &= src_reg
+ * BPF_OR *(uint *) (dst_reg + off16) |= src_reg
+ * BPF_XOR *(uint *) (dst_reg + off16) ^= src_reg
* BPF_ADD | BPF_FETCH src_reg = atomic_fetch_add(dst_reg + off16, src_reg);
+ * BPF_AND | BPF_FETCH src_reg = atomic_fetch_and(dst_reg + off16, src_reg);
+ * BPF_OR | BPF_FETCH src_reg = atomic_fetch_or(dst_reg + off16, src_reg);
+ * BPF_XOR | BPF_FETCH src_reg = atomic_fetch_xor(dst_reg + off16, src_reg);
* BPF_XCHG src_reg = atomic_xchg(dst_reg + off16, src_reg)
* BPF_CMPXCHG r0 = atomic_cmpxchg(dst_reg + off16, r0, src_reg)
*/
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 7b52affc5bd8..4399890b7584 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1642,6 +1642,9 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
STX_ATOMIC_W:
switch (IMM) {
ATOMIC_ALU_OP(BPF_ADD, add)
+ ATOMIC_ALU_OP(BPF_AND, and)
+ ATOMIC_ALU_OP(BPF_OR, or)
+ ATOMIC_ALU_OP(BPF_XOR, xor)
#undef ATOMIC_ALU_OP
case BPF_XCHG:
diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c
index ee8d1132767b..19ff8fed7f4b 100644
--- a/kernel/bpf/disasm.c
+++ b/kernel/bpf/disasm.c
@@ -80,6 +80,13 @@ const char *const bpf_alu_string[16] = {
[BPF_END >> 4] = "endian",
};
+static const char *const bpf_atomic_alu_string[16] = {
+ [BPF_ADD >> 4] = "add",
+ [BPF_AND >> 4] = "and",
+ [BPF_OR >> 4] = "or",
+ [BPF_XOR >> 4] = "or",
+};
+
static const char *const bpf_ldst_string[] = {
[BPF_W >> 3] = "u32",
[BPF_H >> 3] = "u16",
@@ -154,17 +161,23 @@ void print_bpf_insn(const struct bpf_insn_cbs *cbs,
insn->dst_reg,
insn->off, insn->src_reg);
else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
- insn->imm == BPF_ADD) {
- verbose(cbs->private_data, "(%02x) lock *(%s *)(r%d %+d) += r%d\n",
+ (insn->imm == BPF_ADD || insn->imm == BPF_ADD ||
+ insn->imm == BPF_OR || insn->imm == BPF_XOR)) {
+ verbose(cbs->private_data, "(%02x) lock *(%s *)(r%d %+d) %s r%d\n",
insn->code,
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->dst_reg, insn->off,
+ bpf_alu_string[BPF_OP(insn->imm) >> 4],
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->imm == (BPF_ADD | BPF_FETCH) ||
+ insn->imm == (BPF_AND | BPF_FETCH) ||
+ insn->imm == (BPF_OR | BPF_FETCH) ||
+ insn->imm == (BPF_XOR | BPF_FETCH))) {
+ verbose(cbs->private_data, "(%02x) r%d = atomic%s_fetch_%s((%s *)(r%d %+d), r%d)\n",
insn->code, insn->src_reg,
BPF_SIZE(insn->code) == BPF_DW ? "64" : "",
+ bpf_atomic_alu_string[BPF_OP(insn->imm) >> 4],
bpf_ldst_string[BPF_SIZE(insn->code) >> 3],
insn->dst_reg, insn->off, insn->src_reg);
} else if (BPF_MODE(insn->code) == BPF_ATOMIC &&
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index b1226bcd9765..d980c5207e50 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3612,6 +3612,12 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
switch (insn->imm) {
case BPF_ADD:
case BPF_ADD | BPF_FETCH:
+ case BPF_AND:
+ case BPF_AND | BPF_FETCH:
+ case BPF_OR:
+ case BPF_OR | BPF_FETCH:
+ case BPF_XOR:
+ case BPF_XOR | BPF_FETCH:
case BPF_XCHG:
case BPF_CMPXCHG:
break;
diff --git a/tools/include/linux/filter.h b/tools/include/linux/filter.h
index d75998b0d5ac..736bdeccdfe4 100644
--- a/tools/include/linux/filter.h
+++ b/tools/include/linux/filter.h
@@ -173,7 +173,13 @@
* Atomic operations:
*
* BPF_ADD *(uint *) (dst_reg + off16) += src_reg
+ * BPF_AND *(uint *) (dst_reg + off16) &= src_reg
+ * BPF_OR *(uint *) (dst_reg + off16) |= src_reg
+ * BPF_XOR *(uint *) (dst_reg + off16) ^= src_reg
* BPF_ADD | BPF_FETCH src_reg = atomic_fetch_add(dst_reg + off16, src_reg);
+ * BPF_AND | BPF_FETCH src_reg = atomic_fetch_and(dst_reg + off16, src_reg);
+ * BPF_OR | BPF_FETCH src_reg = atomic_fetch_or(dst_reg + off16, src_reg);
+ * BPF_XOR | BPF_FETCH src_reg = atomic_fetch_xor(dst_reg + off16, src_reg);
* BPF_XCHG src_reg = atomic_xchg(dst_reg + off16, src_reg)
* BPF_CMPXCHG r0 = atomic_cmpxchg(dst_reg + off16, r0, src_reg)
*/
--
2.29.2.684.gfbc64c5ab5-goog
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