Re: [RFC PATCH 1/2] lsm: introduce new hook security_vm_execstack

[Casey Schaufler <casey@schaufler-ca.com>]

On 3/15/2024 11:30 AM, Christian Göttsche wrote:
> On Fri, 15 Mar 2024 at 19:22, Casey Schaufler <casey@schaufler-ca.com> wrote:
>> On 3/15/2024 11:08 AM, Christian Göttsche wrote:
>>> Add a new hook guarding instantiations of programs with executable
>>> stack.  They are being warned about since commit 47a2ebb7f505 ("execve:
>>> warn if process starts with executable stack").  Lets give LSMs the
>>> ability to control their presence on a per application basis.
>> This seems like a hideously expensive way to implement a flag
>> disallowing execution of programs with executable stacks. What's
>> wrong with adding a flag VM_NO_EXECUTABLE_STACK?
> That would be global and not on a per application basis.
> One might want to exempt known legacy programs.

OK, I can see that.

> Also is performance a concern for this today's rare occurrence?

Performance is *always* a concern. You're adding a new hook list
for a "rare" case. You're extended SELinux policy to include the
case. This really should be a hardening feature, not an SELinux policy
feature. The hook makes no sense for an LSM like Smack, which only
implements subject+object controls. You could implement a stand alone
LSM that implements only this hook, but again, it's not really access
control, it's hardening.