On Mon, May 9, 2022 at 3:44 PM Joanne Koong <joannelkoong@xxxxxxxxx> wrote:
>
> This patch adds the bulk of the verifier work for supporting dynamic
> pointers (dynptrs) in bpf. This patch implements malloc-type dynptrs
> through 2 new APIs (bpf_dynptr_alloc and bpf_dynptr_put) that can be
> called by a bpf program. Malloc-type dynptrs are dynptrs that dynamically
> allocate memory on behalf of the program.
>
> A bpf_dynptr is opaque to the bpf program. It is a 16-byte structure
> defined internally as:
>
> struct bpf_dynptr_kern {
> void *data;
> u32 size;
> u32 offset;
> } __aligned(8);
>
> The upper 8 bits of *size* is reserved (it contains extra metadata about
> read-only status and dynptr type); consequently, a dynptr only supports
> memory less than 16 MB.
>
> The 2 new APIs for malloc-type dynptrs are:
>
> long bpf_dynptr_alloc(u32 size, u64 flags, struct bpf_dynptr *ptr);
> void bpf_dynptr_put(struct bpf_dynptr *ptr);
>
> Please note that there *must* be a corresponding bpf_dynptr_put for
> every bpf_dynptr_alloc (even if the alloc fails). This is enforced
> by the verifier.
>
> In the verifier, dynptr state information will be tracked in stack
> slots. When the program passes in an uninitialized dynptr
> (ARG_PTR_TO_DYNPTR | MEM_UNINIT), the stack slots corresponding
> to the frame pointer where the dynptr resides at are marked STACK_DYNPTR.
>
> For helper functions that take in initialized dynptrs (eg
> bpf_dynptr_read + bpf_dynptr_write which are added later in this
> patchset), the verifier enforces that the dynptr has been initialized
> properly by checking that their corresponding stack slots have been marked
> as STACK_DYNPTR. Dynptr release functions (eg bpf_dynptr_put) will clear
> the stack slots. The verifier enforces at program exit that there are no
> referenced dynptrs that haven't been released.
>
> Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
> ---
> include/linux/bpf.h | 62 ++++++++-
> include/linux/bpf_verifier.h | 21 +++
> include/uapi/linux/bpf.h | 30 +++++
> kernel/bpf/helpers.c | 75 +++++++++++
> kernel/bpf/verifier.c | 228 ++++++++++++++++++++++++++++++++-
> scripts/bpf_doc.py | 2 +
> tools/include/uapi/linux/bpf.h | 30 +++++
> 7 files changed, 445 insertions(+), 3 deletions(-)
>
Apart from what Daniel and Alexei are discussing, LGTM
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
[...]
