linux-kernel - Re: [PATCH] selinux: optimize major part with a kernel config in selinux_mmap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <0fcac6a8-4ab8-91bc-34e0-cbbb81da3973@schaufler-ca.com>
Date:   Mon, 17 Jul 2023 13:31:41 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Paul Moore <paul@...l-moore.com>, Leesoo Ahn <lsahn@...eel.net>
Cc:     lsahn@...akecorp.com,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>, selinux@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH] selinux: optimize major part with a kernel config in
 selinux_mmap_addr()

On 7/17/2023 1:13 PM, Paul Moore wrote:
> On Mon, Jul 10, 2023 at 4:25 AM Leesoo Ahn <lsahn@...eel.net> wrote:
>> The major part, the conditional branch in selinux_mmap_addr() is always to be
>> false so long as CONFIG_LSM_MMAP_MIN_ADDR is set to zero at compile time.
>>
>> This usually happens in some linux distros, for instance Ubuntu, which
>> the config is set to zero in release version. Therefore it could be a bit
>> optimized with '#if <expr>' at compile time.
>>
>> Signed-off-by: Leesoo Ahn <lsahn@...akecorp.com>
>> ---
>>  security/selinux/hooks.c | 2 ++
>>  1 file changed, 2 insertions(+)
> First, I agree with Stephen's comments that you should ask your distro
> (you mentioned Debian) to move MIN_ADDR higher.  Beyond that, I have
> one request, see below ...
>
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index d06e350fedee..a049aab6524b 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -3723,11 +3723,13 @@ static int selinux_mmap_addr(unsigned long addr)
>>  {
>>         int rc = 0;
>>
>> +#if CONFIG_LSM_MMAP_MIN_ADDR > 0
>>         if (addr < CONFIG_LSM_MMAP_MIN_ADDR) {
>>                 u32 sid = current_sid();
>>                 rc = avc_has_perm(sid, sid, SECCLASS_MEMPROTECT,
>>                                   MEMPROTECT__MMAP_ZERO, NULL);
>>         }
>> +#endif
>>
>>         return rc;
>>  }
> Pre-processor conditionals inside a function are generally something
> we don't recommend.  In this case I would suggest doing something like
> this:
>
> #if (MMAP_MIN_ADDR > 0)
> static int selinux_mmap_addr(...)
> {
>   /* current func definition */
> }
> #else /* MMAP_MIN_ADDR > 0 */
> static int selinux_mmap_addr(...)
> {
>   return 0;
> }
> #endif /* MMAP_MIN_ADDR > 0 */

Better yet, skip the #else here and #if out the LSM_HOOK_INIT(mmap_addr, ...).
No hook at all is faster than a hook that does nothing.