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bpf: Perform CFG walk for exception callback

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Since exception callbacks are not referenced using bpf_pseudo_func and
bpf_pseudo_call instructions, check_cfg traversal will never explore
instructions of the exception callback. Even after adding the subprog,
the program will then fail with a 'unreachable insn' error.

We thus need to begin walking from the start of the exception callback
again in check_cfg after a complete CFG traversal finishes, so as to
explore the CFG rooted at the exception callback.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20230912233214.1518551-8-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kumar Kartikeya Dwivedi 2023-09-13 01:32:04 +02:00 committed by Alexei Starovoitov
parent b9ae0c9dd0
commit b62bf8a5e9
1 changed files with 13 additions and 2 deletions
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15
kernel/bpf/verifier.c
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@ -15126,8 +15126,8 @@ static int check_cfg(struct bpf_verifier_env *env)
{
int insn_cnt = env->prog->len;
int *insn_stack, *insn_state;
int ret = 0;
int i;
int ex_insn_beg, i, ret = 0;
bool ex_done = false;
insn_state = env->cfg.insn_state = kvcalloc(insn_cnt, sizeof(int), GFP_KERNEL);
if (!insn_state)
@ -15143,6 +15143,7 @@ static int check_cfg(struct bpf_verifier_env *env)
insn_stack[0] = 0; /* 0 is the first instruction */
env->cfg.cur_stack = 1;
walk_cfg:
while (env->cfg.cur_stack > 0) {
int t = insn_stack[env->cfg.cur_stack - 1];
@ -15169,6 +15170,16 @@ static int check_cfg(struct bpf_verifier_env *env)
goto err_free;
}
if (env->exception_callback_subprog && !ex_done) {
ex_insn_beg = env->subprog_info[env->exception_callback_subprog].start;
insn_state[ex_insn_beg] = DISCOVERED;
insn_stack[0] = ex_insn_beg;
env->cfg.cur_stack = 1;
ex_done = true;
goto walk_cfg;
}
for (i = 0; i < insn_cnt; i++) {
if (insn_state[i] != EXPLORED) {
verbose(env, "unreachable insn %d\n", i);