linux-kernel - [PATCH v2 1/9] KVM: x86: Remove emulator's broken checks on CR0/CR3/CR4 loads

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Message-Id: <20210422022128.3464144-2-seanjc@google.com>
Date:   Wed, 21 Apr 2021 19:21:20 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Babu Moger <babu.moger@....com>,
        Joao Martins <joao.m.martins@...cle.com>,
        David Woodhouse <dwmw@...zon.co.uk>
Subject: [PATCH v2 1/9] KVM: x86: Remove emulator's broken checks on
 CR0/CR3/CR4 loads

Remove the emulator's checks for illegal CR0, CR3, and CR4 values, as
the checks are redundant, outdated, and in the case of SEV's C-bit,
broken.  The emulator manually calculates MAXPHYADDR from CPUID and
neglects to mask off the C-bit.  For all other checks, kvm_set_cr*() are
a superset of the emulator checks, e.g. see CR4.LA57.

Fixes: a780a3ea6282 ("KVM: X86: Fix reserved bits check for MOV to CR3")
Cc: Babu Moger <babu.moger@....com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/emulate.c | 68 +-----------------------------------------
 1 file changed, 1 insertion(+), 67 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index f7970ba6219f..f4273b8e31fa 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4230,75 +4230,9 @@ static int check_cr_read(struct x86_emulate_ctxt *ctxt)
 
 static int check_cr_write(struct x86_emulate_ctxt *ctxt)
 {
-	u64 new_val = ctxt->src.val64;
-	int cr = ctxt->modrm_reg;
-	u64 efer = 0;
-
-	static u64 cr_reserved_bits[] = {
-		0xffffffff00000000ULL,
-		0, 0, 0, /* CR3 checked later */
-		CR4_RESERVED_BITS,
-		0, 0, 0,
-		CR8_RESERVED_BITS,
-	};
-
-	if (!valid_cr(cr))
+	if (!valid_cr(ctxt->modrm_reg))
 		return emulate_ud(ctxt);
 
-	if (new_val & cr_reserved_bits[cr])
-		return emulate_gp(ctxt, 0);
-
-	switch (cr) {
-	case 0: {
-		u64 cr4;
-		if (((new_val & X86_CR0_PG) && !(new_val & X86_CR0_PE)) ||
-		    ((new_val & X86_CR0_NW) && !(new_val & X86_CR0_CD)))
-			return emulate_gp(ctxt, 0);
-
-		cr4 = ctxt->ops->get_cr(ctxt, 4);
-		ctxt->ops->get_msr(ctxt, MSR_EFER, &efer);
-
-		if ((new_val & X86_CR0_PG) && (efer & EFER_LME) &&
-		    !(cr4 & X86_CR4_PAE))
-			return emulate_gp(ctxt, 0);
-
-		break;
-		}
-	case 3: {
-		u64 rsvd = 0;
-
-		ctxt->ops->get_msr(ctxt, MSR_EFER, &efer);
-		if (efer & EFER_LMA) {
-			u64 maxphyaddr;
-			u32 eax, ebx, ecx, edx;
-
-			eax = 0x80000008;
-			ecx = 0;
-			if (ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx,
-						 &edx, true))
-				maxphyaddr = eax & 0xff;
-			else
-				maxphyaddr = 36;
-			rsvd = rsvd_bits(maxphyaddr, 63);
-			if (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_PCIDE)
-				rsvd &= ~X86_CR3_PCID_NOFLUSH;
-		}
-
-		if (new_val & rsvd)
-			return emulate_gp(ctxt, 0);
-
-		break;
-		}
-	case 4: {
-		ctxt->ops->get_msr(ctxt, MSR_EFER, &efer);
-
-		if ((efer & EFER_LMA) && !(new_val & X86_CR4_PAE))
-			return emulate_gp(ctxt, 0);
-
-		break;
-		}
-	}
-
 	return X86EMUL_CONTINUE;
 }
 
-- 
2.31.1.498.g6c1eba8ee3d-goog