From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Yang Jihong <yangjihong1@huawei.com>
Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
martin.lau@linux.dev, song@kernel.org, yhs@fb.com,
john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com,
haoluo@google.com, jolsa@kernel.org, illusionist.neo@gmail.com,
davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
pabeni@redhat.com, mykolal@fb.com, shuah@kernel.org,
benjamin.tissoires@redhat.com, memxor@gmail.com, delyank@fb.com,
asavkov@redhat.com, bpf@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH bpf RESEND 2/4] bpf: Remove size check for sk in bpf_skb_is_valid_access for 32-bit architecture
Date: Thu, 3 Nov 2022 11:23:08 +0000 [thread overview]
Message-ID: <Y2OknBtLgqTHSrvy@shell.armlinux.org.uk> (raw)
In-Reply-To: <20221103092118.248600-3-yangjihong1@huawei.com>
On Thu, Nov 03, 2022 at 05:21:16PM +0800, Yang Jihong wrote:
> The error code -EACCES is returned when bpf prog is tested in 32-bit environment,
> This is because bpf_object__relocate modifies the instruction to change memory
> size to 4 bytes, as shown in the following messages:
>
> libbpf: prog 'kfunc_call_test1': relo #2: matching candidate #0 <byte_off> [18342] struct __sk_buff.sk (0:30:0 @ offset 168)
> libbpf: prog 'kfunc_call_test1': relo #2: patched insn #1 (LDX/ST/STX) off 168 -> 168
> libbpf: prog 'kfunc_call_test1': relo #2: patched insn #1 (LDX/ST/STX) mem_sz 8 -> 4
>
> As a result, the bpf_skb_is_valid_access check fails. For 32-bit architecture,
> unnecessary checks need to be deleted.
Isn't the purpose of this check to ensure that the entire pointer is
written, and BPF can't write half of it?
> case offsetof(struct __sk_buff, sk):
> - if (type == BPF_WRITE || size != sizeof(__u64))
> - return false;
Wouldn't "(size != sizeof(struct bpf_sock *) && size != sizeof(__u64))"
be more appropriate here, so 32-bit can only write the 32-bit pointer
or the full 64-bit value, and 64-bit can only write the 64-bit pointer?
Or is there a reason not to? bpf folk?
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
WARNING: multiple messages have this Message-ID (diff)
From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Yang Jihong <yangjihong1@huawei.com>
Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
martin.lau@linux.dev, song@kernel.org, yhs@fb.com,
john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com,
haoluo@google.com, jolsa@kernel.org, illusionist.neo@gmail.com,
davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
pabeni@redhat.com, mykolal@fb.com, shuah@kernel.org,
benjamin.tissoires@redhat.com, memxor@gmail.com, delyank@fb.com,
asavkov@redhat.com, bpf@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
linux-kselftest@vger.kernel.org
Subject: Re: [PATCH bpf RESEND 2/4] bpf: Remove size check for sk in bpf_skb_is_valid_access for 32-bit architecture
Date: Thu, 3 Nov 2022 11:23:08 +0000 [thread overview]
Message-ID: <Y2OknBtLgqTHSrvy@shell.armlinux.org.uk> (raw)
In-Reply-To: <20221103092118.248600-3-yangjihong1@huawei.com>
On Thu, Nov 03, 2022 at 05:21:16PM +0800, Yang Jihong wrote:
> The error code -EACCES is returned when bpf prog is tested in 32-bit environment,
> This is because bpf_object__relocate modifies the instruction to change memory
> size to 4 bytes, as shown in the following messages:
>
> libbpf: prog 'kfunc_call_test1': relo #2: matching candidate #0 <byte_off> [18342] struct __sk_buff.sk (0:30:0 @ offset 168)
> libbpf: prog 'kfunc_call_test1': relo #2: patched insn #1 (LDX/ST/STX) off 168 -> 168
> libbpf: prog 'kfunc_call_test1': relo #2: patched insn #1 (LDX/ST/STX) mem_sz 8 -> 4
>
> As a result, the bpf_skb_is_valid_access check fails. For 32-bit architecture,
> unnecessary checks need to be deleted.
Isn't the purpose of this check to ensure that the entire pointer is
written, and BPF can't write half of it?
> case offsetof(struct __sk_buff, sk):
> - if (type == BPF_WRITE || size != sizeof(__u64))
> - return false;
Wouldn't "(size != sizeof(struct bpf_sock *) && size != sizeof(__u64))"
be more appropriate here, so 32-bit can only write the 32-bit pointer
or the full 64-bit value, and 64-bit can only write the 64-bit pointer?
Or is there a reason not to? bpf folk?
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
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next prev parent reply other threads:[~2022-11-03 11:23 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-03 9:21 [PATCH bpf RESEND 0/4] bpf: Support kernel function call in 32-bit ARM Yang Jihong
2022-11-03 9:21 ` Yang Jihong
2022-11-03 9:21 ` [PATCH bpf RESEND 1/4] bpf: Adapt 32-bit return value kfunc for 32-bit ARM when zext extension Yang Jihong
2022-11-03 9:21 ` Yang Jihong
2022-11-03 9:21 ` [PATCH bpf RESEND 2/4] bpf: Remove size check for sk in bpf_skb_is_valid_access for 32-bit architecture Yang Jihong
2022-11-03 9:21 ` Yang Jihong
2022-11-03 11:23 ` Russell King (Oracle) [this message]
2022-11-03 11:23 ` Russell King (Oracle)
2022-11-03 18:15 ` Alexei Starovoitov
2022-11-03 18:15 ` Alexei Starovoitov
2022-11-04 22:43 ` Andrii Nakryiko
2022-11-04 22:43 ` Andrii Nakryiko
2022-11-04 23:37 ` Alexei Starovoitov
2022-11-04 23:37 ` Alexei Starovoitov
2022-11-07 9:22 ` Yang Jihong
2022-11-07 9:22 ` Yang Jihong
2022-11-07 9:12 ` Yang Jihong
2022-11-07 9:12 ` Yang Jihong
2022-11-03 9:21 ` [PATCH bpf RESEND 3/4] bpf: Add kernel function call support in 32-bit ARM Yang Jihong
2022-11-03 9:21 ` Yang Jihong
2022-11-03 11:35 ` Russell King (Oracle)
2022-11-03 11:35 ` Russell King (Oracle)
2022-11-07 9:10 ` Yang Jihong
2022-11-07 9:10 ` Yang Jihong
2022-11-03 9:21 ` [PATCH bpf RESEND 4/4] bpf:selftests: Add kfunc_call test for mixing 32-bit and 64-bit parameters Yang Jihong
2022-11-03 9:21 ` Yang Jihong
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