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bpf: Don't mark arguments to fentry/fexit programs as trusted.

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The PTR_TRUSTED flag should only be applied to pointers where the verifier can
guarantee that such pointers are valid.
The fentry/fexit/fmod_ret programs are not in this category.
Only arguments of SEC("tp_btf") and SEC("iter") programs are trusted
(which have BPF_TRACE_RAW_TP and BPF_TRACE_ITER attach_type correspondingly)

This bug was masked because convert_ctx_accesses() was converting trusted
loads into BPF_PROBE_MEM loads. Fix it as well.
The loads from trusted pointers don't need exception handling.

Fixes: 3f00c5239344 ("bpf: Allow trusted pointers to be passed to KF_TRUSTED_ARGS kfuncs")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20221124215314.55890-1-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2022-11-24 13:53:14 -08:00 committed by Daniel Borkmann
parent 6099754a14
commit c6b0337f01
2 changed files with 13 additions and 6 deletions
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16
kernel/bpf/btf.c
View File

@ -5821,9 +5821,19 @@ static u32 get_ctx_arg_idx(struct btf *btf, const struct btf_type *func_proto,
return nr_args + 1;
}
static bool prog_type_args_trusted(enum bpf_prog_type prog_type)
static bool prog_args_trusted(const struct bpf_prog *prog)
{
return prog_type == BPF_PROG_TYPE_TRACING || prog_type == BPF_PROG_TYPE_STRUCT_OPS;
enum bpf_attach_type atype = prog->expected_attach_type;
switch (prog->type) {
case BPF_PROG_TYPE_TRACING:
return atype == BPF_TRACE_RAW_TP || atype == BPF_TRACE_ITER;
case BPF_PROG_TYPE_LSM:
case BPF_PROG_TYPE_STRUCT_OPS:
return true;
default:
return false;
}
}
bool btf_ctx_access(int off, int size, enum bpf_access_type type,
@ -5969,7 +5979,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
}
info->reg_type = PTR_TO_BTF_ID;
if (prog_type_args_trusted(prog->type))
if (prog_args_trusted(prog))
info->reg_type |= PTR_TRUSTED;
if (tgt_prog) {

3
kernel/bpf/verifier.c
View File

@ -14905,7 +14905,6 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
break;
case PTR_TO_BTF_ID:
case PTR_TO_BTF_ID | PTR_UNTRUSTED:
case PTR_TO_BTF_ID | PTR_TRUSTED:
/* PTR_TO_BTF_ID | MEM_ALLOC always has a valid lifetime, unlike
* PTR_TO_BTF_ID, and an active ref_obj_id, but the same cannot
* be said once it is marked PTR_UNTRUSTED, hence we must handle
@ -14913,8 +14912,6 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
* for this case.
*/
case PTR_TO_BTF_ID | MEM_ALLOC | PTR_UNTRUSTED:
case PTR_TO_BTF_ID | PTR_UNTRUSTED | PTR_TRUSTED:
case PTR_TO_BTF_ID | PTR_UNTRUSTED | MEM_ALLOC | PTR_TRUSTED:
if (type == BPF_READ) {
insn->code = BPF_LDX | BPF_PROBE_MEM |
BPF_SIZE((insn)->code);