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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Wed, 22 Nov 2023 16:51:23 -0800
Message-ID: <CAADnVQKhpjt0pojdYGXpeyMvJnCUVvyrRKCmHg3cKYjAs-HDmA@mail.gmail.com>
Subject: Re: [PATCH 2/2] x86/cfi,bpf: Fix BPF JIT call
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        "David S. Miller" <davem@davemloft.net>,
        David Ahern <dsahern@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>,
        Yonghong Song <yonghong.song@linux.dev>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Sami Tolvanen <samitolvanen@google.com>,
        Kees Cook <keescook@chromium.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
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        linux-arch <linux-arch@vger.kernel.org>,
        clang-built-linux <llvm@lists.linux.dev>,
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On Wed, Nov 22, 2023 at 4:41=E2=80=AFAM Peter Zijlstra <peterz@infradead.or=
g> wrote:
>
>
> +/*
> + * Emit the various CFI preambles, see the large comment about FineIBT
> + * in arch/x86/kernel/alternative.c

.. and in cfi.h ..
which will have a copy-paste from your other email?

>                 prog->bpf_func =3D (void *)image + ctx.prog_offset;
>                 prog->jited =3D 1;
>                 prog->jited_len =3D proglen - ctx.prog_offset; // XXX?

Just drop XXX.

> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1431,6 +1431,9 @@ struct bpf_prog_aux {
>         struct bpf_kfunc_desc_tab *kfunc_tab;
>         struct bpf_kfunc_btf_tab *kfunc_btf_tab;
>         u32 size_poke_tab;
> +#ifdef CONFIG_FINEIBT
> +       struct bpf_ksym ksym_prefix;
> +#endif
>         struct bpf_ksym ksym;
>         const struct bpf_prog_ops *ops;
>         struct bpf_map **used_maps;
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -683,6 +683,23 @@ void bpf_prog_kallsyms_add(struct bpf_pr
>         fp->aux->ksym.prog =3D true;
>
>         bpf_ksym_add(&fp->aux->ksym);
> +
> +#ifdef CONFIG_FINEIBT
> +       /*
> +        * When FineIBT, code in the __cfi_foo() symbols can get executed
> +        * and hence unwinder needs help.
> +        */

I like the idea!

> +       if (cfi_mode !=3D CFI_FINEIBT)
> +               return;

The cfi_mode var needs to be global along with enum ?
Or some new helper function from arch/x86 ?

> +
> +       snprintf(fp->aux->ksym_prefix.name, KSYM_NAME_LEN,
> +                "__cfi_%s", fp->aux->ksym.name);
> +
> +       prog->aux->ksym_prefix.start =3D (unsigned long) prog->bpf_func -=
 16;
> +       prog->aux->ksym_prefix.end   =3D (unsigned long) prog->bpf_func;
> +
> +       bpf_ksym_add(&fp->aux->ksym_prefix);
> +#endif
>  }
>
>  void bpf_prog_kallsyms_del(struct bpf_prog *fp)

and handle deletion of ksym_prefix here.

I think it's shaping up nicely.
Pls resend both patches as a set and cc bpf @ vger.
BPF CI will pick it up and test on arm64, x86-64, s390 with gcc and clang.
We don't do CONFIG_*IBT testing automatically, but
I can manually try that after the holidays.