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

[PATCH v1] 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>
---
 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;
 }
 
 /**
-- 
2.52.0.223.gf5cc29aaa4-goog

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

[Steven Rostedt]

On Tue,  9 Dec 2025 14:40:24 -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.

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@google.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




>  }
>  
>  /**