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

Song Liu
2025-03-01T00:37:41Z

On Fri, Feb 28, 2025 at 8:53 AM Blaise Boscaccy
<bboscaccy@linux.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@linux.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