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Date: Wed, 14 Oct 2020 16:09:33 -0700 From: Andrii Nakryiko <andrii.nakryiko@...il.com> To: Alexei Starovoitov <alexei.starovoitov@...il.com> Cc: "David S. Miller" <davem@...emloft.net>, Daniel Borkmann <daniel@...earbox.net>, john fastabend <john.fastabend@...il.com>, Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, Kernel Team <kernel-team@...com> Subject: Re: [PATCH bpf-next] bpf: Fix register equivalence tracking. On Wed, Oct 14, 2020 at 10:59 AM Alexei Starovoitov <alexei.starovoitov@...il.com> wrote: > > From: Alexei Starovoitov <ast@...nel.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. > 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 <ast@...nel.org> > --- Number of underscores is a bit subtle a difference, but this fixes the bug, so: Acked-by: Andrii Nakryiko <andrii@...nel.org> > kernel/bpf/verifier.c | 38 ++++++++++++------- > .../testing/selftests/bpf/verifier/regalloc.c | 26 +++++++++++++ > 2 files changed, 51 insertions(+), 13 deletions(-) > [...]
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