From: Hao Luo <haoluo@google.com>
To: Andrii Nakryiko <andrii@kernel.org>
Cc: bpf <bpf@vger.kernel.org>, Networking <netdev@vger.kernel.org>,
Alexei Starovoitov <ast@fb.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v2 bpf-next 5/7] bpf: support BPF ksym variables in kernel modules
Date: Mon, 11 Jan 2021 10:59:46 -0800 [thread overview]
Message-ID: <CA+khW7jTso5Jz6D8Scn8-Kf3OtT0B4JP_rJWFCZa8EEmYOO8iw@mail.gmail.com> (raw)
In-Reply-To: <20210108220930.482456-6-andrii@kernel.org>
Acked-by: Hao Luo <haoluo@google.com>, with a suggestion on adding a comment.
On Fri, Jan 8, 2021 at 2:09 PM Andrii Nakryiko <andrii@kernel.org> wrote:
>
> Add support for directly accessing kernel module variables from BPF programs
> using special ldimm64 instructions. This functionality builds upon vmlinux
> ksym support, but extends ldimm64 with src_reg=BPF_PSEUDO_BTF_ID to allow
> specifying kernel module BTF's FD in insn[1].imm field.
>
> During BPF program load time, verifier will resolve FD to BTF object and will
> take reference on BTF object itself and, for module BTFs, corresponding module
> as well, to make sure it won't be unloaded from under running BPF program. The
> mechanism used is similar to how bpf_prog keeps track of used bpf_maps.
>
> One interesting change is also in how per-CPU variable is determined. The
> logic is to find .data..percpu data section in provided BTF, but both vmlinux
> and module each have their own .data..percpu entries in BTF. So for module's
> case, the search for DATASEC record needs to look at only module's added BTF
> types. This is implemented with custom search function.
>
> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> ---
> include/linux/bpf.h | 10 +++
> include/linux/bpf_verifier.h | 3 +
> include/linux/btf.h | 3 +
> kernel/bpf/btf.c | 31 +++++++-
> kernel/bpf/core.c | 23 ++++++
> kernel/bpf/verifier.c | 149 ++++++++++++++++++++++++++++-------
> 6 files changed, 189 insertions(+), 30 deletions(-)
[...]
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 17270b8404f1..af94c6871ab8 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -9703,6 +9703,31 @@ static int do_check(struct bpf_verifier_env *env)
> return 0;
> }
>
> +static int find_btf_percpu_datasec(struct btf *btf)
> +{
> + const struct btf_type *t;
> + const char *tname;
> + int i, n;
> +
It would be good to add a short comment here explaining the reason why
the search for DATASEC in the module case needs to skip entries.
> + n = btf_nr_types(btf);
> + if (btf_is_module(btf))
> + i = btf_nr_types(btf_vmlinux);
> + else
> + i = 1;
> +
> + for(; i < n; i++) {
> + t = btf_type_by_id(btf, i);
> + if (BTF_INFO_KIND(t->info) != BTF_KIND_DATASEC)
> + continue;
> +
> + tname = btf_name_by_offset(btf, t->name_off);
> + if (!strcmp(tname, ".data..percpu"))
> + return i;
> + }
> +
> + return -ENOENT;
> +}
[...]
> 2.24.1
>
next prev parent reply other threads:[~2021-01-11 19:00 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-08 22:09 [PATCH v2 bpf-next 0/7] Support kernel module ksym variables Andrii Nakryiko
2021-01-08 22:09 ` [PATCH v2 bpf-next 1/7] bpf: add bpf_patch_call_args prototype to include/linux/bpf.h Andrii Nakryiko
2021-01-11 4:02 ` Yonghong Song
2021-01-08 22:09 ` [PATCH v2 bpf-next 2/7] bpf: avoid warning when re-casting __bpf_call_base into __bpf_call_base_args Andrii Nakryiko
2021-01-11 4:03 ` Yonghong Song
2021-01-08 22:09 ` [PATCH v2 bpf-next 3/7] bpf: declare __bpf_free_used_maps() unconditionally Andrii Nakryiko
2021-01-11 4:03 ` Yonghong Song
2021-01-08 22:09 ` [PATCH v2 bpf-next 4/7] selftests/bpf: sync RCU before unloading bpf_testmod Andrii Nakryiko
2021-01-11 4:05 ` Yonghong Song
2021-01-11 18:59 ` Hao Luo
2021-01-08 22:09 ` [PATCH v2 bpf-next 5/7] bpf: support BPF ksym variables in kernel modules Andrii Nakryiko
2021-01-11 4:13 ` Yonghong Song
2021-01-11 21:29 ` Andrii Nakryiko
2021-01-12 1:25 ` Yonghong Song
2021-01-11 18:59 ` Hao Luo [this message]
2021-01-11 21:31 ` Andrii Nakryiko
2021-01-08 22:09 ` [PATCH v2 bpf-next 6/7] libbpf: support kernel module ksym externs Andrii Nakryiko
2021-01-11 4:15 ` Yonghong Song
2021-01-11 21:37 ` Andrii Nakryiko
2021-01-12 1:34 ` Yonghong Song
2021-01-12 6:45 ` Andrii Nakryiko
2021-01-11 19:00 ` Hao Luo
2021-01-11 21:39 ` Andrii Nakryiko
2021-01-08 22:09 ` [PATCH v2 bpf-next 7/7] selftests/bpf: test " Andrii Nakryiko
2021-01-11 4:18 ` Yonghong Song
2021-01-11 21:40 ` Andrii Nakryiko
2021-01-11 19:00 ` Hao Luo
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