diff options
| author | Dave Marchevsky <davemarchevsky@fb.com> | 2022-09-12 08:45:44 -0700 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2022-09-15 02:44:07 -0700 |
| commit | 47e34cb74d376ddfeaef94abb1d6dfb3c905ee51 (patch) | |
| tree | 7dc529478d51d5a2142c19b54413e5220dbd78d3 /kernel/bpf/helpers.c | |
| parent | 1bfe26fb082724be453e4d7fd9bb358e3ba669b2 (diff) | |
bpf: Add verifier check for BPF_PTR_POISON retval and arg
BPF_PTR_POISON was added in commit c0a5a21c25f37 ("bpf: Allow storing
referenced kptr in map") to denote a bpf_func_proto btf_id which the
verifier will replace with a dynamically-determined btf_id at verification
time.
This patch adds verifier 'poison' functionality to BPF_PTR_POISON in
order to prepare for expanded use of the value to poison ret- and
arg-btf_id in ongoing work, namely rbtree and linked list patchsets
[0, 1]. Specifically, when the verifier checks helper calls, it assumes
that BPF_PTR_POISON'ed ret type will be replaced with a valid type before
- or in lieu of - the default ret_btf_id logic. Similarly for arg btf_id.
If poisoned btf_id reaches default handling block for either, consider
this a verifier internal error and fail verification. Otherwise a helper
w/ poisoned btf_id but no verifier logic replacing the type will cause a
crash as the invalid pointer is dereferenced.
Also move BPF_PTR_POISON to existing include/linux/posion.h header and
remove unnecessary shift.
[0]: lore.kernel.org/bpf/20220830172759.4069786-1-davemarchevsky@fb.com
[1]: lore.kernel.org/bpf/20220904204145.3089-1-memxor@gmail.com
Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220912154544.1398199-1-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf/helpers.c')
| -rw-r--r-- | kernel/bpf/helpers.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index fc08035f14ed..41aeaf3862ec 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -15,6 +15,7 @@ #include <linux/ctype.h> #include <linux/jiffies.h> #include <linux/pid_namespace.h> +#include <linux/poison.h> #include <linux/proc_ns.h> #include <linux/security.h> #include <linux/btf_ids.h> @@ -1376,10 +1377,9 @@ BPF_CALL_2(bpf_kptr_xchg, void *, map_value, void *, ptr) } /* Unlike other PTR_TO_BTF_ID helpers the btf_id in bpf_kptr_xchg() - * helper is determined dynamically by the verifier. + * helper is determined dynamically by the verifier. Use BPF_PTR_POISON to + * denote type that verifier will determine. */ -#define BPF_PTR_POISON ((void *)((0xeB9FUL << 2) + POISON_POINTER_DELTA)) - static const struct bpf_func_proto bpf_kptr_xchg_proto = { .func = bpf_kptr_xchg, .gpl_only = false, |