The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.14.y git checkout FETCH_HEAD git cherry-pick -x 4984563823f0034d3533854c1b50e729f5191089 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2023050635-saggy-margarita-f21b@gregkh' --subject-prefix 'PATCH 4.14.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 4984563823f0034d3533854c1b50e729f5191089 Mon Sep 17 00:00:00 2001 From: Sean Christopherson seanjc@google.com Date: Tue, 4 Apr 2023 17:23:59 -0700 Subject: [PATCH] KVM: nVMX: Emulate NOPs in L2, and PAUSE if it's not intercepted

Extend VMX's nested intercept logic for emulated instructions to handle "pause" interception, in quotes because KVM's emulator doesn't filter out NOPs when checking for nested intercepts. Failure to allow emulation of NOPs results in KVM injecting a #UD into L2 on any NOP that collides with the emulator's definition of PAUSE, i.e. on all single-byte NOPs.

For PAUSE itself, honor L1's PAUSE-exiting control, but ignore PLE to avoid unnecessarily injecting a #UD into L2. Per the SDM, the first execution of PAUSE after VM-Entry is treated as the beginning of a new loop, i.e. will never trigger a PLE VM-Exit, and so L1 can't expect any given execution of PAUSE to deterministically exit.

... the processor considers this execution to be the first execution of PAUSE in a loop. (It also does so for the first execution of PAUSE at CPL 0 after VM entry.)

All that said, the PLE side of things is currently a moot point, as KVM doesn't expose PLE to L1.

Note, vmx_check_intercept() is still wildly broken when L1 wants to intercept an instruction, as KVM injects a #UD instead of synthesizing a nested VM-Exit. That issue extends far beyond NOP/PAUSE and needs far more effort to fix, i.e. is a problem for the future.

Fixes: 07721feee46b ("KVM: nVMX: Don't emulate instructions in guest mode") Cc: Mathias Krause minipli@grsecurity.net Cc: stable@vger.kernel.org Reviewed-by: Paolo Bonzini pbonzini@redhat.com Link: https://lore.kernel.org/r/20230405002359.418138-1-seanjc@google.com Signed-off-by: Sean Christopherson seanjc@google.com

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index d7bf14abdba1..e06fcd6144b0 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -7935,6 +7935,21 @@ static int vmx_check_intercept(struct kvm_vcpu *vcpu, /* FIXME: produce nested vmexit and return X86EMUL_INTERCEPTED. */ break;

+ case x86_intercept_pause: + /* + * PAUSE is a single-byte NOP with a REPE prefix, i.e. collides + * with vanilla NOPs in the emulator. Apply the interception + * check only to actual PAUSE instructions. Don't check + * PAUSE-loop-exiting, software can't expect a given PAUSE to + * exit, i.e. KVM is within its rights to allow L2 to execute + * the PAUSE. + */ + if ((info->rep_prefix != REPE_PREFIX) || + !nested_cpu_has2(vmcs12, CPU_BASED_PAUSE_EXITING)) + return X86EMUL_CONTINUE; + + break; + /* TODO: check more intercepts... */ default: break;