Re: [RFC PATCH 3/3] nSVM: use svm->nested.save to load vmcb12 registers and avoid TOC/TOU races
From: Maxim Levitsky <hidden>
Date: 2021-09-14 09:12:36
Also in:
lkml
On Tue, 2021-09-14 at 12:02 +0300, Maxim Levitsky wrote:
On Tue, 2021-09-14 at 10:20 +0200, Emanuele Giuseppe Esposito wrote:quoted
On 12/09/2021 12:42, Maxim Levitsky wrote:quoted
quoted
- if (!nested_vmcb_valid_sregs(vcpu, &vmcb12->save) || + if (!nested_vmcb_valid_sregs(vcpu, &svm->nested.save) || !nested_vmcb_check_controls(vcpu, &svm->nested.ctl)) {If you use a different struct for the copied fields, then it makes sense IMHO to drop the 'control' parameter from nested_vmcb_check_controls, and just use the svm->nested.save there directly.Ok, what you say in patch 2 makes sense to me. I can create a new struct vmcb_save_area_cached, but I need to keep nested.ctl because 1) it is used also elsewhere, and different fields from the one checked here are read/set and 2) using another structure (or the sameYes, keep nested.ctl, since vast majority of the fields are copied I think.
But actually that you mention it, I'll say why not to create vmcb_control_area_cached as well indeed and change the type of svm->nested.save to it. (in a separate patch) I see what you mean that we modify it a bit (but we shoudn't to be honest) and such, but all of this can be fixed. The advantage of having vmcb_control_area_cached is that it becomes impossible to use by mistake a non copied field from the guest. It would also emphasize that this stuff came from the guest and should be treated as a toxic waste. Note again that this should be done if we agree as a separate patch.
Best regards, Maxim Levitskyquoted
vmcb_save_area_cached) in its place would just duplicate the same fields of nested.ctl, creating even more confusion and possible inconsistency. Let me know if you disagree. Thank you, Emanuele