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

Steven Rostedt
2025-12-10T02:31:50Z

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

> }
>
> /**