linux-kernel - Re: [PATCH 1/1] security: Propagate caller information in bpf hooks

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Message-ID: <CAPhsuW4bsiD56PivQRLs6jrWGpiWt+4vfcdQ4YA-KWONxLYv9g@mail.gmail.com>
Date: Fri, 28 Feb 2025 16:37:29 -0800
From: Song Liu <song@...nel.org>
To: Blaise Boscaccy <bboscaccy@...ux.microsoft.com>
Cc: Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>, 
	"Serge E. Hallyn" <serge@...lyn.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Yonghong Song <yonghong.song@...ux.dev>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Stephen Smalley <stephen.smalley.work@...il.com>, 
	Ondrej Mosnacek <omosnace@...hat.com>, linux-security-module@...r.kernel.org, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org, selinux@...r.kernel.org
Subject: Re: [PATCH 1/1] security: Propagate caller information in bpf hooks

On Fri, Feb 28, 2025 at 8:53 AM Blaise Boscaccy
<bboscaccy@...ux.microsoft.com> wrote:
>
> Certain bpf syscall subcommands are available for usage from both
> userspace and the kernel. LSM modules or eBPF gatekeeper programs may
> need to take a different course of action depending on whether or not
> a BPF syscall originated from the kernel or userspace.
>
> Additionally, some of the bpf_attr struct fields contain pointers to
> arbitrary memory. Currently the functionality to determine whether or
> not a pointer refers to kernel memory or userspace memory is exposed
> to the bpf verifier, but that information is missing from various LSM
> hooks.
>
> Here we augment the LSM hooks to provide this data, by simply passing
> a boolean flag indicating whether or not the call originated in the
> kernel, in any hook that contains a bpf_attr struct that corresponds
> to a subcommand that may be called from the kernel.
>
> Signed-off-by: Blaise Boscaccy <bboscaccy@...ux.microsoft.com>
> ---
>  include/linux/lsm_hook_defs.h |  6 +++---
>  include/linux/security.h      | 12 ++++++------
>  kernel/bpf/syscall.c          | 10 +++++-----
>  security/security.c           | 17 ++++++++++-------
>  security/selinux/hooks.c      |  6 +++---
>  5 files changed, 27 insertions(+), 24 deletions(-)

tools/testing/selftests/bpf/progs/test_cgroup1_hierarchy.c
has a BPF program for security_bpf(), please also update it.

>
> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> index e2f1ce37c41ef..25f4e74c173be 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -426,14 +426,14 @@ LSM_HOOK(void, LSM_RET_VOID, audit_rule_free, void *lsmrule)
>  #endif /* CONFIG_AUDIT */
>
>  #ifdef CONFIG_BPF_SYSCALL
> -LSM_HOOK(int, 0, bpf, int cmd, union bpf_attr *attr, unsigned int size)
> +LSM_HOOK(int, 0, bpf, int cmd, union bpf_attr *attr, bool is_kernel, unsigned int size)

I think we should add is_kernel to the end of the argument list. This will cause
fewer issues for existing users.

Thanks,
Song