diff mbox series

[bpf-next,1/2] bpf: Allow invoking kfuncs from BPF_PROG_TYPE_SYSCALL progs

Message ID 20240404010308.334604-1-void@manifault.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series [bpf-next,1/2] bpf: Allow invoking kfuncs from BPF_PROG_TYPE_SYSCALL progs | expand

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bpf/vmtest-bpf-next-PR success PR summary
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Commit Message

David Vernet April 4, 2024, 1:03 a.m. UTC 
Currently, a set of core BPF kfuncs (e.g. bpf_task_*, bpf_cgroup_*,
bpf_cpumask_*, etc) cannot be invoked from BPF_PROG_TYPE_SYSCALL
programs. The whitelist approach taken for enabling kfuncs makes sense:
it not safe to call these kfuncs from every program type. For example,
it may not be safe to call bpf_task_acquire() in an fentry to
free_task().

BPF_PROG_TYPE_SYSCALL, on the other hand, is a perfectly safe program
type from which to invoke these kfuncs, as it's a very controlled
environment, and we should never be able to run into any of the typical
problems such as recursive invoations, acquiring references on freeing
kptrs, etc. Being able to invoke these kfuncs would be useful, as
BPF_PROG_TYPE_SYSCALL can be invoked with BPF_PROG_RUN, and would
therefore enable user space programs to synchronously call into BPF to
manipulate these kptrs.

This patch therefore enables invoking the aforementioned core kfuncs
from BPF_PROG_TYPE_SYSCALL progs.

Signed-off-by: David Vernet <void@manifault.com>
---
 kernel/bpf/cpumask.c | 1 +
 kernel/bpf/helpers.c | 1 +
 2 files changed, 2 insertions(+)

Comments

Yonghong Song April 4, 2024, 3:32 p.m. UTC | #1 
On 4/3/24 6:03 PM, David Vernet wrote:
> Currently, a set of core BPF kfuncs (e.g. bpf_task_*, bpf_cgroup_*,
> bpf_cpumask_*, etc) cannot be invoked from BPF_PROG_TYPE_SYSCALL
> programs. The whitelist approach taken for enabling kfuncs makes sense:
> it not safe to call these kfuncs from every program type. For example,
> it may not be safe to call bpf_task_acquire() in an fentry to
> free_task().
>
> BPF_PROG_TYPE_SYSCALL, on the other hand, is a perfectly safe program
> type from which to invoke these kfuncs, as it's a very controlled
> environment, and we should never be able to run into any of the typical
> problems such as recursive invoations, acquiring references on freeing
> kptrs, etc. Being able to invoke these kfuncs would be useful, as
> BPF_PROG_TYPE_SYSCALL can be invoked with BPF_PROG_RUN, and would
> therefore enable user space programs to synchronously call into BPF to
> manipulate these kptrs.
>
> This patch therefore enables invoking the aforementioned core kfuncs
> from BPF_PROG_TYPE_SYSCALL progs.
>
> Signed-off-by: David Vernet <void@manifault.com>

Acked-by: Yonghong Song <yonghong.song@linux.dev>
Andrii Nakryiko April 4, 2024, 10:18 p.m. UTC | #2 
On Wed, Apr 3, 2024 at 6:03 PM David Vernet <void@manifault.com> wrote:
>
> Currently, a set of core BPF kfuncs (e.g. bpf_task_*, bpf_cgroup_*,
> bpf_cpumask_*, etc) cannot be invoked from BPF_PROG_TYPE_SYSCALL
> programs. The whitelist approach taken for enabling kfuncs makes sense:
> it not safe to call these kfuncs from every program type. For example,
> it may not be safe to call bpf_task_acquire() in an fentry to
> free_task().
>
> BPF_PROG_TYPE_SYSCALL, on the other hand, is a perfectly safe program
> type from which to invoke these kfuncs, as it's a very controlled
> environment, and we should never be able to run into any of the typical
> problems such as recursive invoations, acquiring references on freeing
> kptrs, etc. Being able to invoke these kfuncs would be useful, as
> BPF_PROG_TYPE_SYSCALL can be invoked with BPF_PROG_RUN, and would
> therefore enable user space programs to synchronously call into BPF to
> manipulate these kptrs.
>
> This patch therefore enables invoking the aforementioned core kfuncs
> from BPF_PROG_TYPE_SYSCALL progs.
>
> Signed-off-by: David Vernet <void@manifault.com>
> ---
>  kernel/bpf/cpumask.c | 1 +
>  kernel/bpf/helpers.c | 1 +
>  2 files changed, 2 insertions(+)
>

Makes sense, but see my comments on patch #2.

Acked-by: Andrii Nakryiko <andrii@kernel.org>

> diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
> index dad0fb1c8e87..33c473d676a5 100644
> --- a/kernel/bpf/cpumask.c
> +++ b/kernel/bpf/cpumask.c
> @@ -474,6 +474,7 @@ static int __init cpumask_kfunc_init(void)
>         ret = bpf_mem_alloc_init(&bpf_cpumask_ma, sizeof(struct bpf_cpumask), false);
>         ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &cpumask_kfunc_set);
>         ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &cpumask_kfunc_set);
> +       ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &cpumask_kfunc_set);
>         return  ret ?: register_btf_id_dtor_kfuncs(cpumask_dtors,
>                                                    ARRAY_SIZE(cpumask_dtors),
>                                                    THIS_MODULE);
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index d9e7aca8ae9e..8cde717137bd 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2653,6 +2653,7 @@ static int __init kfunc_init(void)
>         ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &generic_kfunc_set);
>         ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &generic_kfunc_set);
>         ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &generic_kfunc_set);
> +       ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &generic_kfunc_set);
>         ret = ret ?: register_btf_id_dtor_kfuncs(generic_dtors,
>                                                   ARRAY_SIZE(generic_dtors),
>                                                   THIS_MODULE);
> --
> 2.44.0
>
diff mbox series

Patch

diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c
index dad0fb1c8e87..33c473d676a5 100644
--- a/kernel/bpf/cpumask.c
+++ b/kernel/bpf/cpumask.c
@@ -474,6 +474,7 @@  static int __init cpumask_kfunc_init(void)
 	ret = bpf_mem_alloc_init(&bpf_cpumask_ma, sizeof(struct bpf_cpumask), false);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &cpumask_kfunc_set);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &cpumask_kfunc_set);
+	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &cpumask_kfunc_set);
 	return  ret ?: register_btf_id_dtor_kfuncs(cpumask_dtors,
 						   ARRAY_SIZE(cpumask_dtors),
 						   THIS_MODULE);
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index d9e7aca8ae9e..8cde717137bd 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2653,6 +2653,7 @@  static int __init kfunc_init(void)
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &generic_kfunc_set);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &generic_kfunc_set);
 	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &generic_kfunc_set);
+	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &generic_kfunc_set);
 	ret = ret ?: register_btf_id_dtor_kfuncs(generic_dtors,
 						  ARRAY_SIZE(generic_dtors),
 						  THIS_MODULE);