> On Jul 17, 2024, at 6:01 PM, 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). > > 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. Circling back to my previous comment (did that ever get noticed?), I don’t think this is quite right: https://lore.kernel.org/all/CALCETrWYu=PYJSgyJ-vaa+3BGAry8Jo8xErZLiGR3U5h6+U0tA@xxxxxxxxxxxxxx/ On a basic system configuration, a given path either may or may not be executed. And maybe that path has some integrity check (dm-verity, etc). So the kernel should tell the interpreter/loader whether the target may be executed. All fine. But I think the more complex cases are more interesting, and the “execute a program” process IS NOT BINARY. An attempt to execute can be rejected outright, or it can be allowed *with a change to creds or security context*. It would be entirely reasonable to have a policy that allows execution of non-integrity-checked files but in a very locked down context only. So… shouldn’t a patch series to this effect actually support this?
