On Wed, Jul 17, 2024 at 3:00 AM Mickaël Salaün <mic@xxxxxxxxxxx> wrote: > > On Wed, Jul 17, 2024 at 09:26:22AM +0100, Steve Dower wrote: > > On 17/07/2024 07:33, Jeff Xu wrote: > > > Consider those cases: I think: > > > a> relying purely on userspace for enforcement does't seem to be > > > effective, e.g. it is trivial to call open(), then mmap() it into > > > executable memory. > > > > If there's a way to do this without running executable code that had to pass > > a previous execveat() check, then yeah, it's not effective (e.g. a Python > > interpreter that *doesn't* enforce execveat() is a trivial way to do it). > > > > Once arbitrary code is running, all bets are off. So long as all arbitrary > > code is being checked itself, it's allowed to do things that would bypass > > later checks (and it's up to whoever audited it in the first place to > > prevent this by not giving it the special mark that allows it to pass the > > check). > We will want to define what is considered as "arbitrary code is running" Using an example of ROP, attackers change the return address in stack, e.g. direct the execution flow to a gauge to call "ld.so /tmp/a.out", do you consider "arbitrary code is running" when stack is overwritten ? or after execve() is called. If it is later, this patch can prevent "ld.so /tmp/a.out". > Exactly. As explained in the patches, one crucial prerequisite is that > the executable code is trusted, and the system must provide integrity > guarantees. We cannot do anything without that. This patches series is > a building block to fix a blind spot on Linux systems to be able to > fully control executability. Even trusted executable can have a bug. I'm thinking in the context of ChromeOS, where all its system services are from trusted partitions, and legit code won't load .so from a non-exec mount. But we want to sandbox those services, so even under some kind of ROP attack, the service still won't be able to load .so from /tmp. Of course, if an attacker can already write arbitrary length of data into the stack, it is probably already a game over.
