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Message-ID: <c8727ba1-0d8b-4c42-a4b1-e98bed061b22@linux.dev>
Date: Fri, 15 Mar 2024 11:34:06 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Kui-Feng Lee <sinquersw@...il.com>
Cc: bpf@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
Kees Cook <keescook@...omium.org>,
Christophe Leroy <christophe.leroy@...roup.eu>,
Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>,
Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>, Zi Shen Lim <zlim.lnx@...il.com>,
Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
"David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
Kui-Feng Lee <thinker.li@...il.com>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH bpf-next v3 2/2] bpf: Check return from set_memory_rox()
On 3/15/24 11:11 AM, Kui-Feng Lee wrote:
>> --- a/kernel/bpf/bpf_struct_ops.c
>> +++ b/kernel/bpf/bpf_struct_ops.c
>> @@ -742,8 +742,11 @@ static long bpf_struct_ops_map_update_elem(struct bpf_map
>> *map, void *key,
>> if (err)
>> goto reset_unlock;
>> }
>> - for (i = 0; i < st_map->image_pages_cnt; i++)
>> - arch_protect_bpf_trampoline(st_map->image_pages[i], PAGE_SIZE);
>> + for (i = 0; i < st_map->image_pages_cnt && !err; i++)
>> + err = arch_protect_bpf_trampoline(st_map->image_pages[i], PAGE_SIZE);
>> +
>> + if (err)
>
> nit: Can it be more specific? I mean to check err < 0, so we can reason
> that this function never returns a positive value other than 0.
I think "if (err)" is fine. It is pretty common in other places of the kernel.
Checking "(err < 0)" may actually mean the return value could be positive. At
least it is how bpf_struct_ops.c is using "(err < 0)".
[ An unrelated side note is another (err < 0) check in bpf_struct_ops.c could
have been changed after the recent changes in bpf_struct_ops_prepare_trampoline
which no longer return +val ].
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