On Fri, Sep 23, 2022 at 3:39 PM Kumar Kartikeya Dwivedi
<memxor@xxxxxxxxx> wrote:
>
> 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
My bad, I skipped previous revisions and didn't see this suggestion.
>
> 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
> > >
