LoongArch: BPF: Fix off-by-one error in build_prologue()

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 <vincent.mc.li@gmail.com>
Tested-by: Vincent Li <vincent.mc.li@gmail.com>
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 <hengqi.chen@gmail.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index ea357a3edc094370ab8daff2d489efbe8ecdf91a..2346c0b55043edc4e1584c5a25ca8d2d2b4f5c6c 100644 (file)
--- 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 68586338ecf8591f3c10693ab49f2bf896c14651..f9c569f5394914a8df7268e824daaadba1b3d50f 100644 (file)
--- 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) {                                               \