[v18,02/13] btf: Export bpf_dynptr definition

Commit Message

Roberto Sassu Sept. 19, 2022, 2:27 p.m. UTC

From: Roberto Sassu <[e-mail]>

eBPF dynamic pointers is a new feature recently added to upstream. It binds
together a pointer to a memory area and its size. The internal kernel
structure bpf_dynptr_kern is not accessible by eBPF programs in user space.
They instead see bpf_dynptr, which is then translated to the internal
kernel structure by the eBPF verifier.

The problem is that it is not possible to include at the same time the uapi
include linux/bpf.h and the vmlinux BTF vmlinux.h, as they both contain the
definition of some structures/enums. The compiler complains saying that the
structures/enums are redefined.

As bpf_dynptr is defined in the uapi include linux/bpf.h, this makes it
impossible to include vmlinux.h. However, in some cases, e.g. when using
kfuncs, vmlinux.h has to be included. The only option until now was to
include vmlinux.h and add the definition of bpf_dynptr directly in the eBPF
program source code from linux/bpf.h.

Solve the problem by using the same approach as for bpf_timer (which also
follows the same scheme with the _kern suffix for the internal kernel
structure).

Add the following line in one of the dynamic pointer helpers,
bpf_dynptr_from_mem():

BTF_TYPE_EMIT(struct bpf_dynptr);

Cc: [e-mail]
Cc: Joanne Koong <[e-mail]>
Fixes: 97e03f521050c ("bpf: Add verifier support for dynptrs")
Signed-off-by: Roberto Sassu <[e-mail]>
---
 kernel/bpf/helpers.c | 2 ++
 1 file changed, 2 insertions(+)

Comments

Yonghong Song Sept. 20, 2022, 5:30 a.m. UTC | #1

On 9/19/22 7:27 AM, Roberto Sassu wrote:
> From: Roberto Sassu <[e-mail]>
> 
> eBPF dynamic pointers is a new feature recently added to upstream. It binds
> together a pointer to a memory area and its size. The internal kernel
> structure bpf_dynptr_kern is not accessible by eBPF programs in user space.
> They instead see bpf_dynptr, which is then translated to the internal
> kernel structure by the eBPF verifier.
> 
> The problem is that it is not possible to include at the same time the uapi
> include linux/bpf.h and the vmlinux BTF vmlinux.h, as they both contain the
> definition of some structures/enums. The compiler complains saying that the
> structures/enums are redefined.
> 
> As bpf_dynptr is defined in the uapi include linux/bpf.h, this makes it
> impossible to include vmlinux.h. However, in some cases, e.g. when using
> kfuncs, vmlinux.h has to be included. The only option until now was to
> include vmlinux.h and add the definition of bpf_dynptr directly in the eBPF
> program source code from linux/bpf.h.
> 
> Solve the problem by using the same approach as for bpf_timer (which also
> follows the same scheme with the _kern suffix for the internal kernel
> structure).
> 
> Add the following line in one of the dynamic pointer helpers,
> bpf_dynptr_from_mem():
> 
> BTF_TYPE_EMIT(struct bpf_dynptr);
> 
> Cc: [e-mail]
> Cc: Joanne Koong <[e-mail]>
> Fixes: 97e03f521050c ("bpf: Add verifier support for dynptrs")
> Signed-off-by: Roberto Sassu <[e-mail]>

Acked-by: Yonghong Song <[e-mail]>

[e-mail] Sept. 22, 2022, 1:10 a.m. UTC | #2

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <[e-mail]>:

On Mon, 19 Sep 2022 16:27:54 +0200 you wrote:
> From: Roberto Sassu <[e-mail]>
> 
> eBPF dynamic pointers is a new feature recently added to upstream. It binds
> together a pointer to a memory area and its size. The internal kernel
> structure bpf_dynptr_kern is not accessible by eBPF programs in user space.
> They instead see bpf_dynptr, which is then translated to the internal
> kernel structure by the eBPF verifier.
> 
> [...]

Here is the summary with links:
  - [v18,02/13] btf: Export bpf_dynptr definition
    https://git.kernel.org/bpf/bpf-next/c/00f146413ccb

You are awesome, thank you!

Patch

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 41aeaf3862ec..7ce1f583b929 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1446,6 +1446,8 @@  BPF_CALL_4(bpf_dynptr_from_mem, void *, data, u32, size, u64, flags, struct bpf_
 {
 	int err;
 
+	BTF_TYPE_EMIT(struct bpf_dynptr);
+
 	err = bpf_dynptr_check_size(size);
 	if (err)
 		goto error;