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

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

[Ian Rogers]

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@google.com>
---
Reduce the number of checks as suggested-by Steven Rostedt
<rostedt@goodmis.org>.
v1: https://lore.kernel.org/lkml/20251209224024.2322124-1-irogers@google.com/
---
 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

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

[Masami Hiramatsu]

On Wed,  7 Jan 2026 16:26:25 -0800
Ian Rogers <irogers@google.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@google.com>
> ---
> Reduce the number of checks as suggested-by Steven Rostedt
> <rostedt@goodmis.org>.
> v1: https://lore.kernel.org/lkml/20251209224024.2322124-1-irogers@google.com/

Look good to me.

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