Paul Moore <paul@xxxxxxxxxxxxxx> writes: > On Wed, Feb 26, 2025 at 2:06 AM Song Liu <song@xxxxxxxxxx> wrote: >> On Tue, Feb 25, 2025 at 4:31 PM Blaise Boscaccy >> <bboscaccy@xxxxxxxxxxxxxxxxxxx> 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 >> > the corresponding universal pointer in any hook that contains already >> > contains a bpf_attr struct that corresponds to a subcommand that may >> > be called from the kernel. >> >> I think this information is useful for LSM hooks. > > I've only looked at it quickly, but so far it seems reasonable. I'm > going to take a closer look today. > >> Question: Do we need a full bpfptr_t for these hooks, or just a boolean >> "is_kernel or not"? > > I may be misunderstanding the patch, but what if we swapped the > existing 'union bpf_attr' parameter for a 'bpfptr_t' parameter? That > would allow for both kernel and usermode pointers, complete with a > 'is_kernel' flag; or am I missing something (likely)? > > -- > paul-moore.com bpfptr_t is just a typedef for a sockptr_t, which contains a void pointer and bool, so if we replaced bpf_attr with it, we might lose a bit of type safety going that route. In syscall.c a most of the subcommand handlers have a static int bpf_foo(union bpf_attr *attr, bpfptr_t uattr); pattern that is used. I was trying to mimic for this patch. The actual parts where the is_kernel flag gets used currently, is for pointer chasing/copy stuff, e.g. make_bpfptr(attr->insns, uattr.is_kernel) make_bpfptr(attr->license, uattr.is_kernel) make_bpfptr(attr->fd_array, uattr.is_kernel) and subcommand structs may contain multiple pointers. -blaise
