Hi, Ilya! >>>>> On Fri, 12 Feb 2021 05:04:08 +0100, Ilya Leoshkevich wrote: > test_global_func4 fails on s390 as reported by Yauheni in [1]. > The immediate problem is that the zext code includes the instruction, > whose result needs to be zero-extended, into the zero-extension > patchlet, and if this instruction happens to be a branch, then its > delta is not adjusted. As a result, the verifier rejects the program > later. Thank you for addressing that! > However, according to [2], as far as the verifier's algorithm is > concerned and as specified by the insn_no_def() function, branching > insns do not define anything. This includes call insns, even though > one might argue that they define %r0. I still think that the patching code should be fixed as well, even if it's a separate issue. But I got the attitude. > This means that the real problem is that zero extension kicks in at > all. This happens because clear_caller_saved_regs() sets BPF_REG_0's > subreg_def after global function calls. This can be fixed in many > ways; this patch mimics what helper function call handling already > does. > [1] https://lore.kernel.org/bpf/20200903140542.156624-1-yauheni.kaliuta@xxxxxxxxxx/ > [2] > https://lore.kernel.org/bpf/CAADnVQ+2RPKcftZw8d+B1UwB35cpBhpF5u3OocNh90D9pETPwg@xxxxxxxxxxxxxx/ > Fixes: 51c39bb1d5d1 ("bpf: Introduce function-by-function verification") > Reported-by: Yauheni Kaliuta <yauheni.kaliuta@xxxxxxxxxx> > Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx> > --- > kernel/bpf/verifier.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index beae700bb56e..183fae996ad0 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -5211,8 +5211,9 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn, > subprog); > clear_caller_saved_regs(env, caller->regs); > - /* All global functions return SCALAR_VALUE */ > + /* All global functions return a 64-bit SCALAR_VALUE */ > mark_reg_unknown(env, caller->regs, BPF_REG_0); > + caller->regs[BPF_REG_0].subreg_def = DEF_NOT_SUBREG; > /* continue with next insn after call */ > return 0; > -- > 2.29.2 -- WBR, Yauheni Kaliuta
