linux-kernel - Re: [PATCH] profiling: fix shift-out-of-bounds in profile

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Message-ID: <99b9e091-9e95-5e45-5914-38a938840aa6@i-love.sakura.ne.jp>
Date:   Fri, 13 Aug 2021 22:27:21 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Pavel Skripkin <paskripkin@...il.com>, rostedt@...dmis.org,
        tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org,
        syzbot+e68c89a9510c159d9684@...kaller.appspotmail.com
Subject: Re: [PATCH] profiling: fix shift-out-of-bounds in profile_setup

On 2021/08/13 19:56, Pavel Skripkin wrote:
> I don't get it, sorry. Do you mean, that
> 
> #define MAX_PROF_SHIFT        BITS_PER_LONG
> 
> is better solution here?

Yes, but I feel we don't need to define MAX_PROF_SHIFT because
the type of the integer value which is subjected to shift operation
will be always "unsigned long" and will unlikely change in the future.

>                          And as I understand we can change prof_shift type from "unsigned long" to "unsigned short", rigth?

Yes, "unsigned int" or "unsigned short int", or even "u8" (I don't know
whether compilers generate bad code if "u8" is used). At least, since
get_option() stores result into "int", receiving via "unsigned int" will
be enough.