On Sat, 24 Sept 2022 at 00:14, Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Thu, Sep 22, 2022 at 11:06 PM Dave Marchevsky <davemarchevsky@xxxxxx> wrote:
> >
> > This patch adds support for the following pattern:
> >
> > struct some_data *data = bpf_ringbuf_reserve(&ringbuf, sizeof(struct some_data, 0));
> > if (!data)
> > return;
> > bpf_map_lookup_elem(&another_map, &data->some_field);
> > bpf_ringbuf_submit(data);
> >
> > Currently the verifier does not consider bpf_ringbuf_reserve's
> > PTR_TO_MEM | MEM_ALLOC ret type a valid key input to bpf_map_lookup_elem.
> > Since PTR_TO_MEM is by definition a valid region of memory, it is safe
> > to use it as a key for lookups.
> >
> > Signed-off-by: Dave Marchevsky <davemarchevsky@xxxxxx>
> > Acked-by: Yonghong Song <yhs@xxxxxx>
> > ---
> > v2->v3: lore.kernel.org/bpf/20220914123600.927632-1-davemarchevsky@xxxxxx
> >
> > * Add Yonghong ack, rebase
> >
> > v1->v2: lore.kernel.org/bpf/20220912101106.2765921-1-davemarchevsky@xxxxxx
> >
> > * Move test changes into separate patch - patch 2 in this series.
> > (Kumar, Yonghong). That patch's changelog enumerates specific
> > changes from v1
> > * Remove PTR_TO_MEM addition from this patch - patch 1 (Yonghong)
> > * I don't have a usecase for PTR_TO_MEM w/o MEM_ALLOC
> > * Add "if (!data)" error check to example pattern in this patch
> > (Yonghong)
> > * Remove patch 2 from v1's series, which removed map_key_value_types
> > as it was more-or-less duplicate of mem_types
> > * Now that PTR_TO_MEM isn't added here, more differences between
> > map_key_value_types and mem_types, and no usecase for PTR_TO_BUF,
> > so drop for now.
> >
> > kernel/bpf/verifier.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 6f6d2d511c06..97351ae3e7a7 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -5641,6 +5641,7 @@ static const struct bpf_reg_types map_key_value_types = {
> > PTR_TO_PACKET_META,
> > PTR_TO_MAP_KEY,
> > PTR_TO_MAP_VALUE,
> > + PTR_TO_MEM | MEM_ALLOC,
>
> are there any differences between mem_types and map_key_value_types?
> If not, should we just drop map_key_value_types? mem_types also alloc
> any PTR_TO_MEM (not just ringbuf's MEM_ALLOC) and PTR_TO_BUF
> (tracepoint context structs, I think?)
>
This was discussed here:
https://lore.kernel.org/bpf/CAP01T76YeOQLfYBX+63Z+cbF+xZUH-4FYG3MyNTiKtP8fLPGtw@xxxxxxxxxxxxxx
I guess we can do it, since it may already be triggered using PTR_TO_MAP_VALUE.
Based on my reading that day, it looked as if passing with offset != 0
would fail in all other cases, but I might be missing some other
corner case. I later realised that memcpy does fallback to memmove
when it detects overlap, so it wouldn't lead to any corruption, just a
warning at runtime.
> > },
> > };
> >
> > --
> > 2.30.2
> >
