Re: [PATCH bpf-next 1/2] bpf: Fix gotox target validation against CFG

[Eduard Zingerman <eddyz87@gmail.com>]

On Tue, 2026-06-09 at 15:56 +0000, Anton Protopopov wrote:
> On 26/06/09 11:03PM, Nuoqi Gui wrote:
> > CFG construction records the modeled gotox target set in
> > insn_aux_data->jt. It includes INSN_ARRAY maps based on whether the map
> > target is in the current subprog. check_indirect_jump() later validates and
> > follows the current PTR_TO_INSN register's actual INSN_ARRAY map. The
> > verifier does not check that targets copied from that map match the targets
> > that CFG construction modeled for this gotox instruction.
> > 
> > This lets one gotox instruction observe two different INSN_ARRAY maps. CFG
> > can select a map whose target is in the current subprog. Another path to
> > the same gotox can carry a PTR_TO_INSN value from a map whose target points
> > at a different subprog. The verifier then accepts an edge absent from the
> > CFG.
> > 
> > On x86, gotox becomes a raw indirect jump in the JIT image. Accepting a
> > target not modeled by CFG can enter another subprog without a matching BPF
> > call frame and crash when executed. Validation observed a GPF in
> > bpf_test_run().
> > 
> > Fix this by requiring every target copied from the actual PTR_TO_INSN map
> > to be present in the CFG jump table built for the current gotox
> > instruction.
> > Reject the program before pushing verifier states for any unmodeled target.
> > 
> > Fixes: 493d9e0d6083 ("bpf, x86: add support for indirect jumps")
> > Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
> > ---
> >  kernel/bpf/verifier.c | 26 ++++++++++++++++++++++++++
> >  1 file changed, 26 insertions(+)
> > 
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index ed7ba0e6a9ce..25fa90e731e3 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -17124,6 +17124,23 @@ static int indirect_jump_min_max_index(struct bpf_verifier_env *env,
> >  	return 0;
> >  }
> >  
> > +static bool is_cfg_indirect_jump_target(struct bpf_verifier_env *env,
> > +					u32 target)
> > +{
> > +	struct bpf_iarray *jt = env->insn_aux_data[env->insn_idx].jt;
> > +	int i;
> > +
> > +	if (!jt)
> > +		return false;
> > +
> > +	for (i = 0; i < jt->cnt; i++) {
> > +		if (jt->items[i] == target)
> > +			return true;
> > +	}
> > +
> > +	return false;
> > +}
> > +
> >  /* gotox *dst_reg */
> >  static int check_indirect_jump(struct bpf_verifier_env *env, struct bpf_insn *insn)
> >  {
> > @@ -17171,6 +17188,15 @@ static int check_indirect_jump(struct bpf_verifier_env *env, struct bpf_insn *in
> >  		return -EINVAL;
> >  	}
> >  
> > +	for (i = 0; i < n; i++) {
> > +		if (!is_cfg_indirect_jump_target(env, env->gotox_tmp_buf->items[i])) {
> > +			verbose(env,
> > +				"gotox target %u from map id=%d is not in the CFG jump table\n",
> > +				env->gotox_tmp_buf->items[i], map->id);
> > +			return -EINVAL;
> > +		}
> > +	}
> 
> Thanks for reporting the bug.
> 
> As for the fix, would it make more sense to either record maps in
> check_cfg or to re-check subfunc boundaries here?

+1 for checking if the jump is within subprog boundaries assumed for the gotox.

> >  	for (i = 0; i < n - 1; i++) {
> >  		mark_indirect_target(env, env->gotox_tmp_buf->items[i]);
> >  		other_branch = push_stack(env, env->gotox_tmp_buf->items[i],
> > 
> > -- 
> > 2.34.1
> >