riscv, bpf: Fix out-of-bounds issue when preparing trampoline image

In the Linux kernel, the following vulnerability has been resolved: riscv, bpf: Fix out-of-bounds issue when preparing trampoline image We get the size of the trampoline image during the dry run phase and allocate memory based on that size. The allocated image will then be populated with instructions during the real patch phase. But after commit 26ef208c209a ("bpf: Use arch_bpf_trampoline_size"), the `im` argument is inconsistent in the dry run and real patch phase. This may cause emit_imm in RV64 to generate a different number of instructions when generating the 'im' address, potentially causing out-of-bounds issues. Let's emit the maximum number of instructions for the "im" address during dry run to fix this problem.

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Linux kernel 安全漏洞

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于 riscv, bpf 模块在准备trampoline image时，由于dry run和实际patch阶段的im参数不一致，可能导致在生成im地址时指令数量不同，引起越界问题。

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