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tools/testing/selftests/bpf/disasm.c
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Merge branch 'bpf: allow ctx writes using BPF_ST_MEM instruction'
Eduard Zingerman says: ==================== Changes v1 -> v2, suggested by Alexei: - Resolved conflict with recent commit: 6fcd486b ("bpf: Refactor RCU enforcement in the verifier"); - Variable `ctx_access` removed in function `convert_ctx_accesses()`; - Macro `BPF_COPY_STORE` renamed to `BPF_EMIT_STORE` and fixed to correctly extract original store instruction class from code. Original message follows: The function verifier.c:convert_ctx_access() applies some rewrites to BPF instructions that read from or write to the BPF program context. For example, the write instruction for the `struct bpf_sockopt::retval` field: *(u32 *)(r1 + offsetof(struct bpf_sockopt, retval)) = r2 Is transformed to: *(u64 *)(r1 + offsetof(struct bpf_sockopt_kern, tmp_reg)) = r9 r9 = *(u64 *)(r1 + offsetof(struct bpf_sockopt_kern, current_task)) r9 = *(u64 *)(r9 + offsetof(struct task_struct, bpf_ctx)) *(u32 *)(r9 + offsetof(struct bpf_cg_run_ctx, retval)) = r2 r9 = *(u64 *)(r1 + offsetof(struct bpf_sockopt_kern, tmp_reg)) Currently, the verifier only supports such transformations for LDX (memory-to-register read) and STX (register-to-memory write) instructions. Error is reported for ST instructions (immediate-to-memory write). This is fine because clang does not currently emit ST instructions. However, new `-mcpu=v4` clang flag is planned, which would allow to emit ST instructions (discussed in [1]). This patch-set adjusts the verifier to support ST instructions in `verifier.c:convert_ctx_access()`. The patches #1 and #2 were previously shared as part of RFC [2]. The changes compared to that RFC are: - In patch #1, a bug in the handling of the `struct __sk_buff::queue_mapping` field was fixed. - Patch #3 is added, which is a set of disassembler-based test cases for context access rewrites. The test cases cover all fields for which the handling code is modified in patch #1. [1] Propose some new instructions for -mcpu=v4 https://lore.kernel.org/bpf/4bfe98be-5333-1c7e-2f6d-42486c8ec039@meta.com/ [2] RFC Support for BPF_ST instruction in LLVM C compiler https://lore.kernel.org/bpf/20221231163122.1360813-1-eddyz87@gmail.com/ [3] v1 https://lore.kernel.org/bpf/20230302225507.3413720-1-eddyz87@gmail.com/ ==================== Signed-off-by:Alexei Starovoitov <ast@kernel.org>