bpf: Introduce BPF nospec instruction for mitigating Spectre v4
stable inclusion from stable-5.10.56 commit bea9e2fd180892eba2574711b05b794f1d0e7b73 bugzilla: 176004 https://gitee.com/openeuler/kernel/issues/I4DYZ4 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bea9e2fd180892eba2574711b05b794f1d0e7b73 -------------------------------- [ Upstream commit f5e81d11 ] In case of JITs, each of the JIT backends compiles the BPF nospec instruction /either/ to a machine instruction which emits a speculation barrier /or/ to /no/ machine instruction in case the underlying architecture is not affected by Speculative Store Bypass or has different mitigations in place already. This covers both x86 and (implicitly) arm64: In case of x86, we use 'lfence' instruction for mitigation. In case of arm64, we rely on the firmware mitigation as controlled via the ssbd kernel parameter. Whenever the mitigation is enabled, it works for all of the kernel code with no need to provide any additional instructions here (hence only comment in arm64 JIT). Other archs can follow as needed. The BPF nospec instruction is specifically targeting Spectre v4 since i) we don't use a serialization barrier for the Spectre v1 case, and ii) mitigation instructions for v1 and v4 might be different on some archs. The BPF nospec is required for a future commit, where the BPF verifier does annotate intermediate BPF programs with speculation barriers. Co-developed-by:Piotr Krysiuk <piotras@gmail.com> Co-developed-by:
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