On Fri, May 19, 2023 at 2:00 AM Dave Hansen <dave.hansen@xxxxxxxxx> wrote: > > 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. I don't think the remote writes are a problem for us if they're initiated from the same process. It's a case of syscalls where we need to add special validation in userspace.
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