On Sat, May 4, 2024 at 6:49 PM Camila Alvarez <cam.alvarez.i@xxxxxxxxx> wrote: > > The error indicates that the verifier is letting through a program with > a stack depth bigger than 512. > > This is due to the verifier not checking the stack depth after > instruction rewrites are perfomed. For example, the MAY_GOTO instruction > adds 8 bytes to the stack, which means that if the stack at the moment > was already 512 bytes it would overflow after rewriting the instruction. This is by design. may_goto and other constructs like bpf_loop inlining can consume a few words above 512 limit. > The fix involves adding a stack depth check after all instruction > rewrites are performed. > > Reported-by: syzbot+d2a2c639d03ac200a4f1@xxxxxxxxxxxxxxxxxxxxxxxxx This syzbot report is likely unrelated. It says that it bisected it to may_goto, but it has this report before may_goto was introduced, so bisection is incorrect. pw-bot: cr > Signed-off-by: Camila Alvarez <cam.alvarez.i@xxxxxxxxx> > --- > kernel/bpf/verifier.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 63749ad5ac6b..a9e23b6b8e8f 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -21285,6 +21285,10 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3 > if (ret == 0) > ret = do_misc_fixups(env); > > + /* max stack depth verification must be done after rewrites as well */ > + if (ret == 0) > + ret = check_max_stack_depth(env); > + > /* do 32-bit optimization after insn patching has done so those patched > * insns could be handled correctly. > */ > -- > 2.34.1 >
