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bpf: Remove superfluous aux sanitation on subprog rejection

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commit 59089a189e3adde4cf85f2ce479738d1ae4c514d upstream.

Follow-up to fe9a5ca7e370 ("bpf: Do not mark insn as seen under speculative
path verification"). The sanitize_insn_aux_data() helper does not serve a
particular purpose in today's code. The original intention for the helper
was that if function-by-function verification fails, a given program would
be cleared from temporary insn_aux_data[], and then its verification would
be re-attempted in the context of the main program a second time.

However, a failure in do_check_subprogs() will skip do_check_main() and
propagate the error to the user instead, thus such situation can never occur.
Given its interaction is not compatible to the Spectre v1 mitigation (due to
comparing aux->seen with env->pass_cnt), just remove sanitize_insn_aux_data()
to avoid future bugs in this area.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Daniel Borkmann 2021-06-29 09:39:15 +00:00 committed by Greg Kroah-Hartman
parent 0e9280654a
commit a11ca29c65
1 changed files with 0 additions and 34 deletions
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34
kernel/bpf/verifier.c
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@ -11707,37 +11707,6 @@ static void free_states(struct bpf_verifier_env *env)
}
}
/* The verifier is using insn_aux_data[] to store temporary data during
* verification and to store information for passes that run after the
* verification like dead code sanitization. do_check_common() for subprogram N
* may analyze many other subprograms. sanitize_insn_aux_data() clears all
* temporary data after do_check_common() finds that subprogram N cannot be
* verified independently. pass_cnt counts the number of times
* do_check_common() was run and insn->aux->seen tells the pass number
* insn_aux_data was touched. These variables are compared to clear temporary
* data from failed pass. For testing and experiments do_check_common() can be
* run multiple times even when prior attempt to verify is unsuccessful.
*
* Note that special handling is needed on !env->bypass_spec_v1 if this is
* ever called outside of error path with subsequent program rejection.
*/
static void sanitize_insn_aux_data(struct bpf_verifier_env *env)
{
struct bpf_insn *insn = env->prog->insnsi;
struct bpf_insn_aux_data *aux;
int i, class;
for (i = 0; i < env->prog->len; i++) {
class = BPF_CLASS(insn[i].code);
if (class != BPF_LDX && class != BPF_STX)
continue;
aux = &env->insn_aux_data[i];
if (aux->seen != env->pass_cnt)
continue;
memset(aux, 0, offsetof(typeof(*aux), orig_idx));
}
}
static int do_check_common(struct bpf_verifier_env *env, int subprog)
{
bool pop_log = !(env->log.level & BPF_LOG_LEVEL2);
@ -11807,9 +11776,6 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
if (!ret && pop_log)
bpf_vlog_reset(&env->log, 0);
free_states(env);
if (ret)
/* clean aux data in case subprog was rejected */
sanitize_insn_aux_data(env);
return ret;
}