linux-kernel - Re: [PATCH v1] tracing: Avoid possible signed 64-bit truncation

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Message-ID: <20251209213135.13eb68f4@fedora>
Date: Tue, 9 Dec 2025 21:31:35 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v1] tracing: Avoid possible signed 64-bit truncation

On Tue,  9 Dec 2025 14:40:24 -0800
Ian Rogers <irogers@...gle.com> wrote:

> 64-bit truncation to 32-bit can result in the sign of the truncated
> value changing. The cmp_mod_entry is used in bsearch and so the
> truncation could result in an invalid search order. This would only
> happen were the addresses more than 2GB apart and so unlikely, but
> let's fix the potentially broken compare anyway.

I'm fine with fixing this but I believe if the addresses are more than
2GB apart there could be other issues elsewhere ;-)

> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  kernel/trace/trace.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index d1e527cf2aae..e6a80cbe9326 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -6057,8 +6057,10 @@ static int cmp_mod_entry(const void *key, const void *pivot)
>  
>  	if (addr >= ent[0].mod_addr && addr < ent[1].mod_addr)
>  		return 0;
> +	else if (addr > ent->mod_addr)
> +		return 1;
>  	else
> -		return addr - ent->mod_addr;
> +		return -1;

Could we still keep this down to a single if check?

	if (addr < ent->mod_addr)
		return -1;

	return addr >= ent[1].mod_addr;

-- Steve




>  }
>  
>  /**