diff mbox series

[v2,bpf-next,2/4] libbpf: Fix relocation of kfunc ksym in ld_imm64 insn.

Message ID 20230317201920.62030-3-alexei.starovoitov@gmail.com (mailing list archive)
State Accepted
Commit 5fc13ad59b60708e52932188854d4d5bf2b0e10e
Delegated to: BPF
Headers show
Series bpf: Add detection of kfuncs. | expand

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Commit Message

Alexei Starovoitov March 17, 2023, 8:19 p.m. UTC 
From: Alexei Starovoitov <ast@kernel.org>

void *p = kfunc; -> generates ld_imm64 insn.
kfunc() -> generates bpf_call insn.

libbpf patches bpf_call insn correctly while only btf_id part of ld_imm64 is
set in the former case. Which means that pointers to kfuncs in modules are not
patched correctly and the verifier rejects load of such programs due to btf_id
being out of range. Fix libbpf to patch ld_imm64 for kfunc.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 tools/lib/bpf/libbpf.c | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Andrii Nakryiko March 17, 2023, 10:49 p.m. UTC | #1 
On Fri, Mar 17, 2023 at 1:19 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> From: Alexei Starovoitov <ast@kernel.org>
>
> void *p = kfunc; -> generates ld_imm64 insn.
> kfunc() -> generates bpf_call insn.
>
> libbpf patches bpf_call insn correctly while only btf_id part of ld_imm64 is
> set in the former case. Which means that pointers to kfuncs in modules are not
> patched correctly and the verifier rejects load of such programs due to btf_id
> being out of range. Fix libbpf to patch ld_imm64 for kfunc.
>
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---
>  tools/lib/bpf/libbpf.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index a557718401e4..4c34fbd7b5be 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -7533,6 +7533,12 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj,
>         ext->is_set = true;
>         ext->ksym.kernel_btf_id = kfunc_id;
>         ext->ksym.btf_fd_idx = mod_btf ? mod_btf->fd_array_idx : 0;
> +       /* Also set kernel_btf_obj_fd to make sure that bpf_object__relocate_data()
> +        * populates FD into ld_imm64 insn when it's used to point to kfunc.
> +        * {kernel_btf_id, btf_fd_idx} -> fixup bpf_call.
> +        * {kernel_btf_id, kernel_btf_obj_fd} -> fixup ld_imm64.
> +        */
> +       ext->ksym.kernel_btf_obj_fd = mod_btf ? mod_btf->fd : 0;
>         pr_debug("extern (func ksym) '%s': resolved to kernel [%d]\n",
>                  ext->name, kfunc_id);

we should report module name here as well, I'll send a patch for both
func and var ksyms

>
> --
> 2.34.1
>
diff mbox series

Patch

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a557718401e4..4c34fbd7b5be 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -7533,6 +7533,12 @@  static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj,
 	ext->is_set = true;
 	ext->ksym.kernel_btf_id = kfunc_id;
 	ext->ksym.btf_fd_idx = mod_btf ? mod_btf->fd_array_idx : 0;
+	/* Also set kernel_btf_obj_fd to make sure that bpf_object__relocate_data()
+	 * populates FD into ld_imm64 insn when it's used to point to kfunc.
+	 * {kernel_btf_id, btf_fd_idx} -> fixup bpf_call.
+	 * {kernel_btf_id, kernel_btf_obj_fd} -> fixup ld_imm64.
+	 */
+	ext->ksym.kernel_btf_obj_fd = mod_btf ? mod_btf->fd : 0;
 	pr_debug("extern (func ksym) '%s': resolved to kernel [%d]\n",
 		 ext->name, kfunc_id);