On Fri, Dec 6, 2024 at 8:11 AM Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> wrote:
>
> An implication of this fix, which follows from the way the raw_tp fixes
> were implemented, is that all PTR_MAYBE_NULL trusted PTR_TO_BTF_ID are
> engulfed by these checks, and PROBE_MEM will apply to all of them, incl.
> those coming from helpers with KF_ACQUIRE returning maybe null trusted
> pointers. This NULL tagging after this commit will be sticky. Compared
> to a solution which only specially tagged raw_tp args with a different
> special maybe null tag (like PTR_SOFT_NULL), it's a consequence of
> overloading PTR_MAYBE_NULL with this meaning.
>
> Fixes: cb4158ce8ec8 ("bpf: Mark raw_tp arguments with PTR_MAYBE_NULL")
> Reported-by: Manu Bretelle <chantra@xxxxxxxx>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> ---
> kernel/bpf/verifier.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 82f40d63ad7b..556fb609d4a4 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -15365,6 +15365,12 @@ static void mark_ptr_or_null_reg(struct bpf_verifier_env *env,
> return;
>
> if (is_null) {
> + /* We never mark a raw_tp trusted pointer as scalar, to
> + * preserve backwards compatibility, instead just leave
> + * it as is.
> + */
> + if (mask_raw_tp_reg_cond(env, reg))
> + return;
The blast radius is getting too big.
Patch 1 is ok, but here we're doubling down on
the hack in commit
cb4158ce8ec8 ("bpf: Mark raw_tp arguments with PTR_MAYBE_NULL")
I think we need to revert the raw_tp masking hack and
go with denylist the way Jiri proposed:
https://lore.kernel.org/bpf/ZrIj9jkXqpKXRuS7@krava/
denylist is certainly less safer and it's a whack-a-mole
comparing to allowlist, but it's much much shorter
according to Jiri's analysis:
https://lore.kernel.org/bpf/Zr3q8ihbe8cUdpfp@krava/
Eduard had an idea how to auto generate such allow/denylist
during the build.
That could be a follow up.
