Re: [PATCH bpf-next v12 4/7] bpf, x86: Support private stack in jit

[Yonghong Song <yonghong.song@linux.dev>]

On 11/12/24 5:13 PM, Alexei Starovoitov wrote:
> On Tue, Nov 12, 2024 at 8:41 AM Yonghong Song <yonghong.song@linux.dev> wrote:
>> +
>> +static void priv_stack_check_guard(void __percpu *priv_stack_ptr, int alloc_size,
>> +                                  struct bpf_prog *prog)
>> +{
>> +       int cpu, underflow_idx = (alloc_size - PRIV_STACK_GUARD_SZ) >> 3;
>> +       u64 *stack_ptr;
>> +
>> +       for_each_possible_cpu(cpu) {
>> +               stack_ptr = per_cpu_ptr(priv_stack_ptr, cpu);
>> +               if (stack_ptr[0] != PRIV_STACK_GUARD_VAL ||
>> +                   stack_ptr[underflow_idx] != PRIV_STACK_GUARD_VAL) {
>> +                       pr_err("BPF private stack overflow/underflow detected for prog %sx\n",
>> +                              bpf_get_prog_name(prog));
>> +                       break;
>> +               }
>> +       }
>> +}
> I was tempted to change pr_err() to WARN() to make sure this kinda bug
> is very obvious, but left it as-is.
> I think kasan-ing JITed load/stores and adding poison to guards
> will be a bigger win.
> The bpf prog/verifier bug will be spotted right away instead of
> later during jit_free.

Agree. I will work on this as a follow-up.