From: "Jose E. Marchesi" <jose.marchesi@oracle.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: bpf@vger.kernel.org, david.faust@oracle.com,
cupertino.miranda@oracle.com,
Eduard Zingerman <eddyz87@gmail.com>,
Yonghong Song <yonghong.song@linux.dev>
Subject: Re: [PATCH bpf-next] bpf: avoid uninitialized value in BPF_CORE_READ_BITFIELD
Date: Tue, 07 May 2024 20:14:04 +0200 [thread overview]
Message-ID: <87v83pcwwj.fsf@oracle.com> (raw)
In-Reply-To: <CAEf4BzZ259J6M+y5xVakycqVPgU3vjP3_qWFMuyZKDkVn68ysg@mail.gmail.com> (Andrii Nakryiko's message of "Tue, 7 May 2024 09:41:47 -0700")
> On Tue, May 7, 2024 at 4:40 AM Jose E. Marchesi
> <jose.marchesi@oracle.com> wrote:
>>
>> GCC warns that `val' may be used uninitialized in the
>> BPF_CORE_READ_BITFIELD macro, defined in bpf_core_read.h as:
>>
>> [...]
>> unsigned long long val; \
>> [...] \
>> switch (__CORE_RELO(s, field, BYTE_SIZE)) { \
>> case 1: val = *(const unsigned char *)p; break; \
>> case 2: val = *(const unsigned short *)p; break; \
>> case 4: val = *(const unsigned int *)p; break; \
>> case 8: val = *(const unsigned long long *)p; break; \
>> } \
>> [...]
>> val; \
>> } \
>>
>> This patch initializes `val' to zero in order to avoid the warning,
>> and random values to be used in case __builtin_preserve_field_info
>> returns unexpected values for BPF_FIELD_BYTE_SIZE.
>>
>> Tested in bpf-next master.
>> No regressions.
>>
>> Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
>> Cc: david.faust@oracle.com
>> Cc: cupertino.miranda@oracle.com
>> Cc: Eduard Zingerman <eddyz87@gmail.com>
>> Cc: Yonghong Song <yonghong.song@linux.dev>
>> ---
>> tools/lib/bpf/bpf_core_read.h | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/lib/bpf/bpf_core_read.h b/tools/lib/bpf/bpf_core_read.h
>> index b5c7ce5c243a..88d129b5f0a1 100644
>> --- a/tools/lib/bpf/bpf_core_read.h
>> +++ b/tools/lib/bpf/bpf_core_read.h
>> @@ -89,7 +89,7 @@ enum bpf_enum_value_kind {
>> */
>> #define BPF_CORE_READ_BITFIELD(s, field) ({ \
>> const void *p = (const void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \
>> - unsigned long long val; \
>> + unsigned long long val = 0; \
>
> let's add instead `default: val = 0; break;`
>
> as Yonghong mentioned, it's not expected to have invalid byte size
> value in the relocation
Ok. I will send a V2 with that change.
> pw-bot: cr
>
>> \
>> /* This is a so-called barrier_var() operation that makes specified \
>> * variable "a black box" for optimizing compiler. \
>> --
>> 2.30.2
>>
>>
prev parent reply other threads:[~2024-05-07 18:14 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-07 11:39 [PATCH bpf-next] bpf: avoid uninitialized value in BPF_CORE_READ_BITFIELD Jose E. Marchesi
2024-05-07 16:23 ` Yonghong Song
2024-05-07 18:13 ` Jose E. Marchesi
2024-05-07 16:41 ` Andrii Nakryiko
2024-05-07 18:14 ` Jose E. Marchesi [this message]
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