Skip to contentSkip to conversation

FAILED: patch "[PATCH] KVM: x86: Remove emulator's broken checks on CR0/CR3/CR4" failed to apply to 5.4-stable tree

PATCH [email protected] 1 participant 1 message May 12, 2021

Subsystems (3)
Stable branch x86 KVM x86
lore
Share & tools
lore

[email protected]

author maintainer
#0 lore raw

The patch below does not apply to the 5.4-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 <[email protected]>.

thanks,

greg k-h

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

From d0fe7b6404408835ed60232cb3bf28324b2f95db Mon Sep 17 00:00:00 2001
From: Sean Christopherson <[email protected]>
Date: Wed, 21 Apr 2021 19:21:20 -0700
Subject: [PATCH] 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Remove the emulator's checks for illegal CR0, CR3, and CR4 values, as the checks are redundant, outdated, and in the case of SEV's C-bit, broken.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 <[email protected]>
Signed-off-by Sean Christopherson <[email protected]>

Message-Id: <[email protected]>

Cc [email protected]
[Unify check_cr_read and check_cr_write. - Paolo]
Signed-off-by Paolo Bonzini <[email protected]>
arch/x86/kvm/emulate.c +3 -77
index f7970ba6219f..abd9a4db11a8 100644
@@ -4220,7 +4220,7 @@ static bool valid_cr(int nr)
 	}
 }
 
-static int check_cr_read(struct x86_emulate_ctxt *ctxt)
+static int check_cr_access(struct x86_emulate_ctxt *ctxt)
 {
 	if (!valid_cr(ctxt->modrm_reg))
 		return emulate_ud(ctxt);

@@ -4228,80 +4228,6 @@ static int check_cr_read(struct x86_emulate_ctxt *ctxt)
 	return X86EMUL_CONTINUE;
 }
 
-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))
-		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;
-}
-
 static int check_dr7_gd(struct x86_emulate_ctxt *ctxt)
 {
 	unsigned long dr7;

@@ -4841,10 +4767,10 @@ static const struct opcode twobyte_table[256] = {
 	D(ImplicitOps | ModRM | SrcMem | NoAccess), /* 8 * reserved NOP */
 	D(ImplicitOps | ModRM | SrcMem | NoAccess), /* NOP + 7 * reserved NOP */
 	/* 0x20 - 0x2F */
-	DIP(ModRM | DstMem | Priv | Op3264 | NoMod, cr_read, check_cr_read),
+	DIP(ModRM | DstMem | Priv | Op3264 | NoMod, cr_read, check_cr_access),
 	DIP(ModRM | DstMem | Priv | Op3264 | NoMod, dr_read, check_dr_read),
 	IIP(ModRM | SrcMem | Priv | Op3264 | NoMod, em_cr_write, cr_write,
-						check_cr_write),
+						check_cr_access),
 	IIP(ModRM | SrcMem | Priv | Op3264 | NoMod, em_dr_write, dr_write,
 						check_dr_write),
 	N, N, N, N,