Patch-mainline: v5.16-rc1
Git-commit: ff8828c84f9376a8c3040da16a88e2c39aa3a527
References: git-fixes
From: Sean Christopherson <seanjc@google.com>
Date: Mon, 20 Sep 2021 17:02:56 -0700
Subject: [PATCH] KVM: x86: Do not mark all registers as avail/dirty during
 RESET/INIT

Do not blindly mark all registers as available+dirty at RESET/INIT, and
instead rely on writes to registers to go through the proper mutators or
to explicitly mark registers as dirty.  INIT in particular does not blindly
overwrite all registers, e.g. select bits in CR0 are preserved across INIT,
thus marking registers available+dirty without first reading the register
from hardware is incorrect.

In practice this is a benign bug as KVM doesn't let the guest control CR0
bits that are preserved across INIT, and all other true registers are
explicitly written during the RESET/INIT flows.  The PDPTRs and EX_INFO
"registers" are not explicitly written, but accessing those values during
RESET/INIT is nonsensical and would be a KVM bug regardless of register
caching.

Fixes: 66f7b72e1171 ("KVM: x86: Make register state after reset conform to specification")
[sean: !!! NOT FOR STABLE !!!]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210921000303.400537-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/kvm/vmx/vmx.c | 1 +
 arch/x86/kvm/x86.c     | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 6323ed6a0746..7c496fd0bb96 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4449,6 +4449,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	}
 
 	vmx_segment_cache_clear(vmx);
+	kvm_register_mark_available(vcpu, VCPU_EXREG_SEGMENTS);
 
 	seg_setup(VCPU_SREG_CS);
 	vmcs_write16(GUEST_CS_SELECTOR, 0xf000);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c25913294f61..629442e3847b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10859,9 +10859,9 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 		vcpu->arch.xcr0 = XFEATURE_MASK_FP;
 	}
 
+	/* All GPRs except RDX (handled below) are zeroed on RESET/INIT. */
 	memset(vcpu->arch.regs, 0, sizeof(vcpu->arch.regs));
-	vcpu->arch.regs_avail = ~0;
-	vcpu->arch.regs_dirty = ~0;
+	kvm_register_mark_dirty(vcpu, VCPU_REGS_RSP);
 
 	vcpu->arch.ia32_xss = 0;
 
-- 
2.35.3