From: Xu Kuohai <xukuohai@huaweicloud.com>
To: Eduard Zingerman <eddyz87@gmail.com>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>,
Edward Cree <ecree.xilinx@gmail.com>
Cc: Yonghong Song <yonghong.song@linux.dev>,
bpf@vger.kernel.org, netdev@vger.kernel.org,
linux-security-module@vger.kernel.org,
linux-kselftest@vger.kernel.org,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>,
Matt Bobrowski <mattbobrowski@google.com>,
Brendan Jackman <jackmanb@chromium.org>,
Paul Moore <paul@paul-moore.com>,
James Morris <jmorris@namei.org>,
"Serge E . Hallyn" <serge@hallyn.com>,
Khadija Kamran <kamrankhadijadj@gmail.com>,
Casey Schaufler <casey@schaufler-ca.com>,
Ondrej Mosnacek <omosnace@redhat.com>,
Kees Cook <keescook@chromium.org>,
John Johansen <john.johansen@canonical.com>,
Lukas Bulwahn <lukas.bulwahn@gmail.com>,
Roberto Sassu <roberto.sassu@huawei.com>,
Shung-Hsi Yu <shung-hsi.yu@suse.com>
Subject: Re: [PATCH bpf-next v3 07/11] bpf: Fix a false rejection caused by AND operation
Date: Tue, 30 Apr 2024 11:56:37 +0800 [thread overview]
Message-ID: <9e49be2a-ec07-4265-a55a-45c1eb19c565@huaweicloud.com> (raw)
In-Reply-To: <7cf8b58011156af99816391d3afd5c52e48ea8b7.camel@gmail.com>
On 4/30/2024 6:18 AM, Eduard Zingerman wrote:
> On Mon, 2024-04-29 at 13:58 -0700, Andrii Nakryiko wrote:
>
> [...]
>
>>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>>> index 8f0f2e21699e..b69c89bc5cfc 100644
>>> --- a/kernel/bpf/verifier.c
>>> +++ b/kernel/bpf/verifier.c
>>> @@ -13478,6 +13478,28 @@ static void scalar32_min_max_and(struct bpf_reg_state *dst_reg,
>>> return;
>>> }
>>>
>>> + /* Special case: dst_reg is in range [-1, 0] */
>>> + if (dst_reg->s32_min_value == -1 && dst_reg->s32_max_value == 0) {
>>> + var32_off = tnum_union(src_reg->var_off, tnum_const(0));
>>> + dst_reg->var_off = tnum_with_subreg(dst_reg->var_off, var32_off);
>>> + dst_reg->u32_min_value = var32_off.value;
>>> + dst_reg->u32_max_value = min(dst_reg->u32_max_value, umax_val);
>>
>> can you explain the logic behing u32 min/max updates, especially that
>> we use completely different values for min/max and it's not clear why
>> u32_min <= u32_max invariant will always hold. Same below
>
> I agree with Andrii here.
> It appears that dst_reg.{min,max} fields should be set as
> {min(src.min, 0), max(src.max, 0)} for both signed and unsigned cases.
> Wdyt?
>
Agree, since 0 is the minimum unsigned number, the result range is
equal to [0, src.u32_max].
>>
>>> + dst_reg->s32_min_value = min_t(s32, src_reg->s32_min_value, 0);
>>> + dst_reg->s32_max_value = max_t(s32, src_reg->s32_max_value, 0);
>>> + return;
>>> + }
>>> +
>>> + /* Special case: src_reg is in range [-1, 0] */
>>> + if (src_reg->s32_min_value == -1 && src_reg->s32_max_value == 0) {
>>> + var32_off = tnum_union(dst_reg->var_off, tnum_const(0));
>>> + dst_reg->var_off = tnum_with_subreg(dst_reg->var_off, var32_off);
>>> + dst_reg->u32_min_value = var32_off.value;
>>> + dst_reg->u32_max_value = min(dst_reg->u32_max_value, umax_val);
>>> + dst_reg->s32_min_value = min_t(s32, dst_reg->s32_min_value, 0);
>>> + dst_reg->s32_max_value = max_t(s32, dst_reg->s32_max_value, 0);
>>> + return;
>>> + }
>>> +
>>> /* We get our minimum from the var_off, since that's inherently
>>> * bitwise. Our maximum is the minimum of the operands' maxima.
>>> */
>
> [...]
next prev parent reply other threads:[~2024-04-30 3:56 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-11 12:27 [PATCH bpf-next v3 00/11] Add check for bpf lsm return value Xu Kuohai
2024-04-11 12:27 ` [PATCH bpf-next v3 01/11] bpf, lsm: Annotate lsm hook return value range Xu Kuohai
2024-04-11 12:27 ` [PATCH bpf-next v3 02/11] bpf, lsm: Add helper to read " Xu Kuohai
2024-04-11 12:27 ` [PATCH bpf-next v3 03/11] bpf, lsm: Check bpf lsm hook return values in verifier Xu Kuohai
2024-04-13 11:44 ` Eduard Zingerman
2024-04-11 12:27 ` [PATCH bpf-next v3 04/11] bpf, lsm: Add bpf lsm disabled hook list Xu Kuohai
2024-04-11 12:27 ` [PATCH bpf-next v3 05/11] bpf: Avoid progs for different hooks calling each other with tail call Xu Kuohai
2024-04-11 12:27 ` [PATCH bpf-next v3 06/11] bpf: Fix compare error in function retval_range_within Xu Kuohai
2024-04-12 8:53 ` Shung-Hsi Yu
2024-04-25 23:41 ` Andrii Nakryiko
2024-04-26 8:08 ` Xu Kuohai
2024-04-11 12:27 ` [PATCH bpf-next v3 07/11] bpf: Fix a false rejection caused by AND operation Xu Kuohai
2024-04-19 23:00 ` Eduard Zingerman
2024-04-20 8:33 ` Xu Kuohai
2024-04-23 21:55 ` Yonghong Song
2024-04-24 2:25 ` Xu Kuohai
2024-04-24 22:06 ` Yonghong Song
2024-04-25 2:42 ` Xu Kuohai
2024-04-25 16:28 ` Yonghong Song
2024-04-26 7:43 ` Xu Kuohai
2024-04-26 20:36 ` Andrii Nakryiko
2024-04-28 15:15 ` Xu Kuohai
2024-04-29 20:58 ` Andrii Nakryiko
2024-04-29 22:18 ` Eduard Zingerman
2024-04-30 3:56 ` Xu Kuohai [this message]
2024-04-30 3:54 ` Xu Kuohai
2024-04-29 21:56 ` Eduard Zingerman
2024-04-11 12:27 ` [PATCH bpf-next v3 08/11] selftests/bpf: Avoid load failure for token_lsm.c Xu Kuohai
2024-04-11 12:27 ` [PATCH bpf-next v3 09/11] selftests/bpf: Add return value checks for failed tests Xu Kuohai
2024-04-11 12:27 ` [PATCH bpf-next v3 10/11] selftests/bpf: Add test for lsm tail call Xu Kuohai
2024-04-11 12:27 ` [PATCH bpf-next v3 11/11] selftests/bpf: Add verifier tests for bpf lsm Xu Kuohai
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