[RFC PATCH bpf-next] bpf: Make actual max tail call count as MAX_TAIL_CALL_CNT

From: Tiezhu Yang
Date: Wed Sep 08 2021 - 04:21:41 EST

Next message: Claudiu Beznea: "[PATCH v2 0/2] irqchip/mchp-eic: add driver for Microchip EIC"
Previous message: Alexandre Bailon: "Re: [PATCH v3 2/4] remoteproc: Add a remoteproc driver for the MT8183's APU"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

In the current code, the actual max tail call count is 33 which is greater
than MAX_TAIL_CALL_CNT, this is not consistent with the intended meaning
in the commit 04fd61ab36ec ("bpf: allow bpf programs to tail-call other
bpf programs"):

"The chain of tail calls can form unpredictable dynamic loops therefore
tail_call_cnt is used to limit the number of calls and currently is set
to 32."

Additionally, after commit 874be05f525e ("bpf, tests: Add tail call test
suite"), we can see there exists failed testcase.

On all archs when CONFIG_BPF_JIT_ALWAYS_ON is not set:
# echo 0 > /proc/sys/net/core/bpf_jit_enable
# modprobe test_bpf
# dmesg | grep -w FAIL
Tail call error path, max count reached jited:0 ret 34 != 33 FAIL

On some archs:
# echo 1 > /proc/sys/net/core/bpf_jit_enable
# modprobe test_bpf
# dmesg | grep -w FAIL
Tail call error path, max count reached jited:1 ret 34 != 33 FAIL

with this patch, make the actual max tail call count as MAX_TAIL_CALL_CNT,
at the same time, the above failed testcase can be fixed.

Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
---

Hi all,

This is a RFC patch, if I am wrong or I missed something,
please let me know, thank you!

arch/arm/net/bpf_jit_32.c | 11 ++++++-----
arch/arm64/net/bpf_jit_comp.c | 7 ++++---
arch/mips/net/ebpf_jit.c | 4 ++--
arch/powerpc/net/bpf_jit_comp32.c | 4 ++--
arch/powerpc/net/bpf_jit_comp64.c | 12 ++++++------
arch/riscv/net/bpf_jit_comp32.c | 4 ++--
arch/riscv/net/bpf_jit_comp64.c | 4 ++--
arch/sparc/net/bpf_jit_comp_64.c | 8 ++++----
kernel/bpf/core.c | 4 ++--
9 files changed, 30 insertions(+), 28 deletions(-)

diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
index a951276..39d9ae9 100644
--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -1180,18 +1180,19 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx)

/* tmp2[0] = array, tmp2[1] = index */

- /* if (tail_call_cnt > MAX_TAIL_CALL_CNT)
- * goto out;
+ /*
* tail_call_cnt++;
+ * if (tail_call_cnt > MAX_TAIL_CALL_CNT)
+ * goto out;
*/
+ tc = arm_bpf_get_reg64(tcc, tmp, ctx);
+ emit(ARM_ADDS_I(tc[1], tc[1], 1), ctx);
+ emit(ARM_ADC_I(tc[0], tc[0], 0), ctx);
lo = (u32)MAX_TAIL_CALL_CNT;
hi = (u32)((u64)MAX_TAIL_CALL_CNT >> 32);
- tc = arm_bpf_get_reg64(tcc, tmp, ctx);
emit(ARM_CMP_I(tc[0], hi), ctx);
_emit(ARM_COND_EQ, ARM_CMP_I(tc[1], lo), ctx);
_emit(ARM_COND_HI, ARM_B(jmp_offset), ctx);
- emit(ARM_ADDS_I(tc[1], tc[1], 1), ctx);
- emit(ARM_ADC_I(tc[0], tc[0], 0), ctx);
arm_bpf_put_reg64(tcc, tmp, ctx);

/* prog = array->ptrs[index]
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 41c23f4..5d6c843 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -286,14 +286,15 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx)
emit(A64_CMP(0, r3, tmp), ctx);
emit(A64_B_(A64_COND_CS, jmp_offset), ctx);

- /* if (tail_call_cnt > MAX_TAIL_CALL_CNT)
- * goto out;
+ /*
* tail_call_cnt++;
+ * if (tail_call_cnt > MAX_TAIL_CALL_CNT)
+ * goto out;
*/
+ emit(A64_ADD_I(1, tcc, tcc, 1), ctx);
emit_a64_mov_i64(tmp, MAX_TAIL_CALL_CNT, ctx);
emit(A64_CMP(1, tcc, tmp), ctx);
emit(A64_B_(A64_COND_HI, jmp_offset), ctx);
- emit(A64_ADD_I(1, tcc, tcc, 1), ctx);

/* prog = array->ptrs[index];
* if (prog == NULL)
diff --git a/arch/mips/net/ebpf_jit.c b/arch/mips/net/ebpf_jit.c
index 3a73e93..029fc34 100644
--- a/arch/mips/net/ebpf_jit.c
+++ b/arch/mips/net/ebpf_jit.c
@@ -617,14 +617,14 @@ static int emit_bpf_tail_call(struct jit_ctx *ctx, int this_idx)
b_off = b_imm(this_idx + 1, ctx);
emit_instr(ctx, bne, MIPS_R_AT, MIPS_R_ZERO, b_off);
/*
- * if (TCC-- < 0)
+ * if (--TCC < 0)
* goto out;
*/
/* Delay slot */
tcc_reg = (ctx->flags & EBPF_TCC_IN_V1) ? MIPS_R_V1 : MIPS_R_S4;
emit_instr(ctx, daddiu, MIPS_R_T5, tcc_reg, -1);
b_off = b_imm(this_idx + 1, ctx);
- emit_instr(ctx, bltz, tcc_reg, b_off);
+ emit_instr(ctx, bltz, MIPS_R_T5, b_off);
/*
* prog = array->ptrs[index];
* if (prog == NULL)
diff --git a/arch/powerpc/net/bpf_jit_comp32.c b/arch/powerpc/net/bpf_jit_comp32.c
index beb12cb..b5585ad 100644
--- a/arch/powerpc/net/bpf_jit_comp32.c
+++ b/arch/powerpc/net/bpf_jit_comp32.c
@@ -221,12 +221,12 @@ static void bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32
PPC_BCC(COND_GE, out);

/*
+ * tail_call_cnt++;
* if (tail_call_cnt > MAX_TAIL_CALL_CNT)
* goto out;
*/
- EMIT(PPC_RAW_CMPLWI(_R0, MAX_TAIL_CALL_CNT));
- /* tail_call_cnt++; */
EMIT(PPC_RAW_ADDIC(_R0, _R0, 1));
+ EMIT(PPC_RAW_CMPLWI(_R0, MAX_TAIL_CALL_CNT));
PPC_BCC(COND_GT, out);

/* prog = array->ptrs[index]; */
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index b87a63d..bb15cc4 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -227,6 +227,12 @@ static void bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32
PPC_BCC(COND_GE, out);

/*
+ * tail_call_cnt++;
+ */
+ EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], b2p[TMP_REG_1], 1));
+ PPC_BPF_STL(b2p[TMP_REG_1], 1, bpf_jit_stack_tailcallcnt(ctx));
+
+ /*
* if (tail_call_cnt > MAX_TAIL_CALL_CNT)
* goto out;
*/
@@ -234,12 +240,6 @@ static void bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32
EMIT(PPC_RAW_CMPLWI(b2p[TMP_REG_1], MAX_TAIL_CALL_CNT));
PPC_BCC(COND_GT, out);

- /*
- * tail_call_cnt++;
- */
- EMIT(PPC_RAW_ADDI(b2p[TMP_REG_1], b2p[TMP_REG_1], 1));
- PPC_BPF_STL(b2p[TMP_REG_1], 1, bpf_jit_stack_tailcallcnt(ctx));
-
/* prog = array->ptrs[index]; */
EMIT(PPC_RAW_MULI(b2p[TMP_REG_1], b2p_index, 8));
EMIT(PPC_RAW_ADD(b2p[TMP_REG_1], b2p[TMP_REG_1], b2p_bpf_array));
diff --git a/arch/riscv/net/bpf_jit_comp32.c b/arch/riscv/net/bpf_jit_comp32.c
index e649742..1608d94 100644
--- a/arch/riscv/net/bpf_jit_comp32.c
+++ b/arch/riscv/net/bpf_jit_comp32.c
@@ -800,12 +800,12 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)

/*
* temp_tcc = tcc - 1;
- * if (tcc < 0)
+ * if (temp_tcc < 0)
* goto out;
*/
emit(rv_addi(RV_REG_T1, RV_REG_TCC, -1), ctx);
off = ninsns_rvoff(tc_ninsn - (ctx->ninsns - start_insn));
- emit_bcc(BPF_JSLT, RV_REG_TCC, RV_REG_ZERO, off, ctx);
+ emit_bcc(BPF_JSLT, RV_REG_T1, RV_REG_ZERO, off, ctx);

/*
* prog = array->ptrs[index];
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index 3af4131..6e9ba83 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -311,12 +311,12 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
off = ninsns_rvoff(tc_ninsn - (ctx->ninsns - start_insn));
emit_branch(BPF_JGE, RV_REG_A2, RV_REG_T1, off, ctx);

- /* if (TCC-- < 0)
+ /* if (--TCC < 0)
* goto out;
*/
emit_addi(RV_REG_T1, tcc, -1, ctx);
off = ninsns_rvoff(tc_ninsn - (ctx->ninsns - start_insn));
- emit_branch(BPF_JSLT, tcc, RV_REG_ZERO, off, ctx);
+ emit_branch(BPF_JSLT, RV_REG_T1, RV_REG_ZERO, off, ctx);

/* prog = array->ptrs[index];
* if (!prog)
diff --git a/arch/sparc/net/bpf_jit_comp_64.c b/arch/sparc/net/bpf_jit_comp_64.c
index 9a2f20c..50d914c 100644
--- a/arch/sparc/net/bpf_jit_comp_64.c
+++ b/arch/sparc/net/bpf_jit_comp_64.c
@@ -863,6 +863,10 @@ static void emit_tail_call(struct jit_ctx *ctx)
emit_branch(BGEU, ctx->idx, ctx->idx + OFFSET1, ctx);
emit_nop(ctx);

+ emit_alu_K(ADD, tmp, 1, ctx);
+ off = BPF_TAILCALL_CNT_SP_OFF;
+ emit(ST32 | IMMED | RS1(SP) | S13(off) | RD(tmp), ctx);
+
off = BPF_TAILCALL_CNT_SP_OFF;
emit(LD32 | IMMED | RS1(SP) | S13(off) | RD(tmp), ctx);
emit_cmpi(tmp, MAX_TAIL_CALL_CNT, ctx);
@@ -870,10 +874,6 @@ static void emit_tail_call(struct jit_ctx *ctx)
emit_branch(BGU, ctx->idx, ctx->idx + OFFSET2, ctx);
emit_nop(ctx);

- emit_alu_K(ADD, tmp, 1, ctx);
- off = BPF_TAILCALL_CNT_SP_OFF;
- emit(ST32 | IMMED | RS1(SP) | S13(off) | RD(tmp), ctx);
-
emit_alu3_K(SLL, bpf_index, 3, tmp, ctx);
emit_alu(ADD, bpf_array, tmp, ctx);
off = offsetof(struct bpf_array, ptrs);
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 9f4636d..8edb1c3 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1564,10 +1564,10 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn)

if (unlikely(index >= array->map.max_entries))
goto out;
- if (unlikely(tail_call_cnt > MAX_TAIL_CALL_CNT))
- goto out;

tail_call_cnt++;
+ if (unlikely(tail_call_cnt > MAX_TAIL_CALL_CNT))
+ goto out;

prog = READ_ONCE(array->ptrs[index]);
if (!prog)
--
2.1.0

Next message: Claudiu Beznea: "[PATCH v2 0/2] irqchip/mchp-eic: add driver for Microchip EIC"
Previous message: Alexandre Bailon: "Re: [PATCH v3 2/4] remoteproc: Add a remoteproc driver for the MT8183's APU"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]