Andrii Nakryiko wrote: > On Wed, Oct 14, 2020 at 10:59 AM Alexei Starovoitov > <alexei.starovoi...@gmail.com> wrote: > > > > From: Alexei Starovoitov <a...@kernel.org> > > > > The 64-bit JEQ/JNE handling in reg_set_min_max() was clearing reg->id in > > either > > true or false branch. In the case 'if (reg->id)' check was done on the other > > branch the counter part register would have reg->id == 0 when called into > > find_equal_scalars(). In such case the helper would incorrectly identify > > other > > registers with id == 0 as equivalent and propagate the state incorrectly.
One thought. It seems we should never have reg->id=0 in find_equal_scalars() would it be worthwhile to add an additional check here? Something like, if (known_reg->id == 0) return Or even a WARN_ON_ONCE() there? Not sold either way, but maybe worth thinking about. > > Fix it by preserving ID across reg_set_min_max(). > > In other words any kind of comparison operator on the scalar register > > should preserve its ID to recognize: > > r1 = r2 > > if (r1 == 20) { > > #1 here both r1 and r2 == 20 > > } else if (r2 < 20) { > > #2 here both r1 and r2 < 20 > > } > > > > The patch is addressing #1 case. The #2 was working correctly already. > > > > Fixes: 75748837b7e5 ("bpf: Propagate scalar ranges through register > > assignments.") > > Signed-off-by: Alexei Starovoitov <a...@kernel.org> > > --- > > Number of underscores is a bit subtle a difference, but this fixes the bug, > so: > > Acked-by: Andrii Nakryiko <and...@kernel.org> > Nice catch, Acked-by: John Fastabend <john.fastab...@gmail.com> > > > kernel/bpf/verifier.c | 38 ++++++++++++------- > > .../testing/selftests/bpf/verifier/regalloc.c | 26 +++++++++++++ > > 2 files changed, 51 insertions(+), 13 deletions(-) > > > > [...]