On Thu, Feb 13, 2025 at 9:03 AM Jiayuan Chen <mrpre@xxxxxxx> wrote:
>
> On Thu, Feb 13, 2025 at 08:02:55AM -0800, Alexei Starovoitov wrote:
> > On Thu, Feb 13, 2025 at 5:13 AM Jiayuan Chen <mrpre@xxxxxxx> wrote:
> > >
> > > may_goto uses an additional 8 bytes on the stack, which causes the
> > > interpreters[] array to go out of bounds when calculating index by
> > > stack_size.
> > >
> > > 1. If a BPF program is rewritten, re-evaluate the stack size. For non-JIT
> > > cases, reject loading directly.
> > >
> > > 2. For non-JIT cases, calculating interpreters[idx] may still cause
> > > out-of-bounds array access, and just warn about it.
> > >
> > > 3. For jit_requested cases, the execution of bpf_func also needs to be
> > > warned. So Move the definition of function __bpf_prog_ret0_warn out of
> > > the macro definition CONFIG_BPF_JIT_ALWAYS_ON
> > >
> [...]
> > > ---
> > > EVAL6(PROG_NAME_LIST, 224, 256, 288, 320, 352, 384)
> > > EVAL4(PROG_NAME_LIST, 416, 448, 480, 512)
> > > };
> > > +
> > > +#define MAX_INTERPRETERS_CALLBACK (sizeof(interpreters) / sizeof(*interpreters))
> >
> > There is ARRAY_SIZE macro.
> Thanks, I will use it.
> >
> > > #undef PROG_NAME_LIST
> > > #define PROG_NAME_LIST(stack_size) PROG_NAME_ARGS(stack_size),
> > > static __maybe_unused
> > > @@ -2290,17 +2293,18 @@ void bpf_patch_call_args(struct bpf_insn *insn, u32 stack_depth)
> > > insn->code = BPF_JMP | BPF_CALL_ARGS;
> > > }
> > > #endif
> > > -#else
> > > +#endif
> > > +
> > > static unsigned int __bpf_prog_ret0_warn(const void *ctx,
> > > const struct bpf_insn *insn)
> > > {
> > > /* If this handler ever gets executed, then BPF_JIT_ALWAYS_ON
> > > - * is not working properly, so warn about it!
> > > + * is not working properly, or interpreter is being used when
> > > + * prog->jit_requested is not 0, so warn about it!
> > > */
> > > WARN_ON_ONCE(1);
> > > return 0;
> > > }
> > > -#endif
> > >
> > > bool bpf_prog_map_compatible(struct bpf_map *map,
> > > const struct bpf_prog *fp)
> > > @@ -2380,8 +2384,14 @@ static void bpf_prog_select_func(struct bpf_prog *fp)
> > > {
> > > #ifndef CONFIG_BPF_JIT_ALWAYS_ON
> > > u32 stack_depth = max_t(u32, fp->aux->stack_depth, 1);
> > > + u32 idx = (round_up(stack_depth, 32) / 32) - 1;
> > >
> > > - fp->bpf_func = interpreters[(round_up(stack_depth, 32) / 32) - 1];
> > > + if (!fp->jit_requested) {
> >
> > I don't think above check is necessary.
> > Why not just
> > if (WARN_ON_ONCE(idx >= ARRAY_SIZE(interpreters)))
> > fp->bpf_func = __bpf_prog_ret0_warn;
> > else
> > fp->bpf_func = interpreters[idx];
> >
>
> When jit_requested is set 1, the stack_depth can still go above 512,
> and we'd end up executing this function, where the index calculation would
> overflow, triggering an array out-of-bounds warning from USCAN or WAR().
Ok, then do:
if (!fp->jit_requested && WARN_ON_ONCE(idx >= ARRAY_SIZE(interpreters)))
> > > + WARN_ON_ONCE(idx >= MAX_INTERPRETERS_CALLBACK);
> > > + fp->bpf_func = interpreters[idx];
since warning and anyway proceeding to access the array out of bounds
is just wrong.
