linux-kernel - Re: [PATCH v2] tracing: Avoid possible signed 64-bit truncation

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Message-Id: <20260108113510.5f0716c539f2ab416fd39ec9@kernel.org>
Date: Thu, 8 Jan 2026 11:35:10 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tracing: Avoid possible signed 64-bit truncation

On Wed,  7 Jan 2026 16:26:25 -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.
> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
> Reduce the number of checks as suggested-by Steven Rostedt
> <rostedt@...dmis.org>.
> v1: https://lore.kernel.org/lkml/20251209224024.2322124-1-irogers@google.com/

Look good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Thanks!

> ---
>  kernel/trace/trace.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 6f2148df14d9..5e2d597b4377 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -6109,10 +6109,10 @@ static int cmp_mod_entry(const void *key, const void *pivot)
>  	unsigned long addr = (unsigned long)key;
>  	const struct trace_mod_entry *ent = pivot;
>  
> -	if (addr >= ent[0].mod_addr && addr < ent[1].mod_addr)
> -		return 0;
> -	else
> -		return addr - ent->mod_addr;
> +	if (addr < ent[0].mod_addr)
> +		return -1;
> +
> +	return addr >= ent[1].mod_addr;
>  }
>  
>  /**
> -- 
> 2.52.0.351.gbe84eed79e-goog
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>