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[bpf-next,6/7] mips: bpf: Fix off-by-one in tail call count limiting

Message ID 20210809093437.876558-7-johan.almbladh@anyfinetworks.com
State New
Headers show
Series Fix MAX_TAIL_CALL_CNT handling in eBPF JITs | expand

Commit Message

Johan Almbladh Aug. 9, 2021, 9:34 a.m. UTC 
Before, the eBPF JIT allowed up to MAX_TAIL_CALL_CNT + 1 tail calls.
Now, precisely MAX_TAIL_CALL_CNT is allowed, which is in line with the
behaviour of the interpreter. Verified with the test_bpf test suite
on qemu-system-mips64.

Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
---
 arch/mips/net/ebpf_jit.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
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Patch

diff --git a/arch/mips/net/ebpf_jit.c b/arch/mips/net/ebpf_jit.c
index 3a73e9375712..a93121d71c80 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, blez, tcc_reg, b_off);
 	/*
 	 * prog = array->ptrs[index];
 	 * if (prog == NULL)