Re: [PATCH bpf-next v2 1/2] bpf, riscv: Add BPF stack arguments support for RV64 JIT

[bot+bpf-ci@kernel.org]

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>     bpf, riscv: Add BPF stack arguments support for RV64 JIT
>
>     Add bpf_jit_supports_stack_args() for the RV64 JIT so BPF subprograms
>     and kfuncs can receive more than 5 arguments via the stack
>     (BPF_REG_PARAMS / r11).
>
>     For BPF-to-BPF calls the caller writes outgoing arguments at the
>     bottom of its frame (SP-relative). The callee reads them with
>     FP-relative loads. Its FP is set to the caller SP in the prologue,
>     so the offsets match.
>
>     The RISC-V ABI puts arguments 6-8 in A5-A7 and arguments 9+ at
>     SP+0. Before each kfunc call, load arguments 6-8 from the outgoing
>     area into A5-A7 and copy any remaining arguments down so argument 9
>     lands at SP+0.
>
>     A5 (BPF_REG_0), A6 (TCC) and A7 are safe to clobber here: R0 is not
>     live before a call, TCC is backed up on the stack, and A7 is unused
>     by the JIT.
>
>     Limit the existing kfunc sign-extension loop to MAX_BPF_FUNC_REG_ARGS
>     iterations; otherwise idx >= 5 resolves to S1-S5 (BPF_R6-FP) and
>     corrupts callee-saved registers.
>
>     Signed-off-by: Feng Jiang <jiangfeng@kylinos.cn>

This looks like a bug fix for stack argument support. The commit message
describes how the sign-extension loop was limited to prevent corruption
of callee-saved registers S1-S5 when idx >= 5. This fixes an issue
introduced by commit 443574b03387 ("riscv, bpf: Fix kfunc parameters
incompatibility between bpf and riscv abi"), which added the
sign-extension loop without limiting it to MAX_BPF_FUNC_REG_ARGS.

Should this include:

  Fixes: 443574b03387 ("riscv, bpf: Fix kfunc parameters incompatibility between bpf and riscv abi")


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