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

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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: 5dc615520c ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Hengqi Chen 2025-03-30 16:31:09 +08:00 committed by Greg Kroah-Hartman
parent f39af67f03
commit e9ccb262b3
2 changed files with 7 additions and 0 deletions
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2
arch/loongarch/net/bpf_jit.c
View File

@ -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;
}

5
arch/loongarch/net/bpf_jit.h
View File

@ -25,6 +25,11 @@ 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) { \