On 5/18/23 15:51, Jeff Xu wrote: >> Do you have a solid handle on all call paths that will reach >> __arch_check_vma_pkey_for_write() and can you ensure they are all >> non-remote? > Is this about the attack scenario where the attacker uses ptrace() > into the chrome process ? if so it is not in our threat model, and > that is more related to sandboxing on the host. The attacker would use *some* remote interface. ptrace() is just one of those remote interfaces. > Or is this about io_uring? Yes, io_uring kernel thread breaks our > expectations of PKRU & user space threads, however I thought the break > is not just for this - any syscall involved in memory operation will > break after into io_uring ? I'm not quite following. Please just do me a favor: have the io_uring maintainers look at your proposal. Make sure that the defenses you are building can work in a process where io_uring is in use by the benign threads. Those same folks are pretty familiar with the other, more traditional I/O syscalls that have in-memory descriptors that control syscall behavior like readv/writev. Those also need a close look. > Other than those, yes, I try to ensure the check is only used at the > beginning of syscall entry in all cases, which should be non-remote I > hope. You're right that synchronous, shallow syscall paths are usually non-remote. But those aren't the problem. The problem is that there *ARE* remote accesses and those are a potential hole for this whole mechanism. Can they be closed? I don't know. I honestly don't have a great grasp on how widespread these things are. You'll need a much more complete grasp on them than I have before this thing can go forward.
