On Tue, Jun 18, 2019 at 8:27 PM Borislav Petkov <bp@xxxxxxxxx> wrote: > > On Tue, Jun 18, 2019 at 08:01:06PM +0200, Dmitry Vyukov wrote: > > I am not a KVM folk either, but FWIW syzkaller is capable of creating > > a double-nested VM. > > Aaaha, there it is. :) > > > The code is somewhat VMX-specific, but it should > > be capable at least executing some SVM instructions inside of guest. > > This code setups VM to run a given instruction sequences (should be generic): > > https://github.com/google/syzkaller/blob/34bf9440bd06034f86b5d9ac8afbf078129cbdae/executor/common_kvm_amd64.h > > The instruction generator is based on Intel XED so it may be somewhat > > Intel-biased, but at least I see some mentions of SVM there: > > https://raw.githubusercontent.com/google/syzkaller/34bf9440bd06034f86b5d9ac8afbf078129cbdae/pkg/ifuzz/gen/all-enc-instructions.txt > > Right, and that right there looks wrong: > > ICLASS : VMLOAD > CPL : 3 > CATEGORY : SYSTEM > EXTENSION : SVM > ATTRIBUTES: PROTECTED_MODE > PATTERN : 0x0F 0x01 MOD[0b11] MOD=3 REG[0b011] RM[0b010] > OPERANDS : REG0=OrAX():r:IMPL > > That is, *if* "CPL: 3" above means in XED context that VMLOAD is > supposed to be run in CPL3, then this is wrong because VMLOAD #GPs if > CPL was not 0. Ditto for VMRUN and a couple of others. > > Perhaps that support was added at some point but not really run on AMD > hw yet... Interesting. I've updated to the latest Intel XED: https://github.com/google/syzkaller/commit/472f0082fd8a2f82b85ab0682086e10b71529a51 And I actually see a number of changes around this for the VMX instructions: ICLASS : VMPTRLD -CPL : 3 +CPL : 0 ICLASS : VMXON -CPL : 3 +CPL : 0 ICLASS : VMLAUNCH -CPL : 3 +CPL : 0 But VMLOAD is still marked as CPL 3. Perhaps it's something to fix in Intel XED. But for syzkaller it should not matter much, it's a fuzzer and it will do all kinds of crazy non-conforming stuff. These CPLs are only used as hints at best if at all. It should sure try CPL=0 instructions in CPL3 regardless.
