From b3ffad2f02db4aace6799fe0049508b8925eae45 Mon Sep 17 00:00:00 2001 From: Hengqi Chen Date: Sun, 30 Mar 2025 16:31:09 +0800 Subject: [PATCH] LoongArch: BPF: Fix off-by-one error in build_prologue() commit 7e2586991e36663c9bc48c828b83eab180ad30a9 upstream. Vincent reported that running BPF progs with tailcalls on LoongArch causes kernel hard lockup. Debugging the issues shows that the JITed image missing a jirl instruction at the end of the epilogue. There are two passes in JIT compiling, the first pass set the flags and the second pass generates JIT code based on those flags. With BPF progs mixing bpf2bpf and tailcalls, build_prologue() generates N insns in the first pass and then generates N+1 insns in the second pass. This makes epilogue_offset off by one and we will jump to some unexpected insn and cause lockup. Fix this by inserting a nop insn. Cc: stable@vger.kernel.org Fixes: 5dc615520c4d ("LoongArch: Add BPF JIT support") Fixes: bb035ef0cc91 ("LoongArch: BPF: Support mixing bpf2bpf and tailcalls") Reported-by: Vincent Li Tested-by: Vincent Li Closes: https://lore.kernel.org/loongarch/CAK3+h2w6WESdBN3UCr3WKHByD7D6Q_Ve1EDAjotVrnx6Or_c8g@mail.gmail.com/ Closes: https://lore.kernel.org/bpf/CAK3+h2woEjG_N=-XzqEGaAeCmgu2eTCUc7p6bP4u8Q+DFHm-7g@mail.gmail.com/ Signed-off-by: Hengqi Chen Signed-off-by: Huacai Chen Signed-off-by: Greg Kroah-Hartman --- arch/loongarch/net/bpf_jit.c | 2 ++ arch/loongarch/net/bpf_jit.h | 5 +++++ 2 files changed, 7 insertions(+) diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c index 6595e992fda85..5f26ad6e0780e 100644 --- a/arch/loongarch/net/bpf_jit.c +++ b/arch/loongarch/net/bpf_jit.c @@ -142,6 +142,8 @@ static void build_prologue(struct jit_ctx *ctx) */ if (seen_tail_call(ctx) && seen_call(ctx)) move_reg(ctx, TCC_SAVED, REG_TCC); + else + emit_insn(ctx, nop); ctx->stack_size = stack_adjust; } diff --git a/arch/loongarch/net/bpf_jit.h b/arch/loongarch/net/bpf_jit.h index 68586338ecf85..f9c569f539491 100644 --- a/arch/loongarch/net/bpf_jit.h +++ b/arch/loongarch/net/bpf_jit.h @@ -27,6 +27,11 @@ struct jit_data { struct jit_ctx ctx; }; +static inline void emit_nop(union loongarch_instruction *insn) +{ + insn->word = INSN_NOP; +} + #define emit_insn(ctx, func, ...) \ do { \ if (ctx->image != NULL) { \ -- 2.47.3