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Subject[PATCH 4.19 008/114] KVM: X86: Fix userspace set invalid CR4
Date
From: Wanpeng Li <wanpengli@tencent.com>

commit 3ca94192278ca8de169d78c085396c424be123b3 upstream.

Reported by syzkaller:

WARNING: CPU: 0 PID: 6544 at /home/kernel/data/kvm/arch/x86/kvm//vmx/vmx.c:4689 handle_desc+0x37/0x40 [kvm_intel]
CPU: 0 PID: 6544 Comm: a.out Tainted: G OE 5.3.0-rc4+ #4
RIP: 0010:handle_desc+0x37/0x40 [kvm_intel]
Call Trace:
vmx_handle_exit+0xbe/0x6b0 [kvm_intel]
vcpu_enter_guest+0x4dc/0x18d0 [kvm]
kvm_arch_vcpu_ioctl_run+0x407/0x660 [kvm]
kvm_vcpu_ioctl+0x3ad/0x690 [kvm]
do_vfs_ioctl+0xa2/0x690
ksys_ioctl+0x6d/0x80
__x64_sys_ioctl+0x1a/0x20
do_syscall_64+0x74/0x720
entry_SYSCALL_64_after_hwframe+0x49/0xbe

When CR4.UMIP is set, guest should have UMIP cpuid flag. Current
kvm set_sregs function doesn't have such check when userspace inputs
sregs values. SECONDARY_EXEC_DESC is enabled on writes to CR4.UMIP
in vmx_set_cr4 though guest doesn't have UMIP cpuid flag. The testcast
triggers handle_desc warning when executing ltr instruction since
guest architectural CR4 doesn't set UMIP. This patch fixes it by
adding valid CR4 and CPUID combination checking in __set_sregs.

syzkaller source: https://syzkaller.appspot.com/x/repro.c?x=138efb99600000

Reported-by: syzbot+0f1819555fbdce992df9@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/x86.c | 38 +++++++++++++++++++++-----------------
1 file changed, 21 insertions(+), 17 deletions(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -791,34 +791,42 @@ int kvm_set_xcr(struct kvm_vcpu *vcpu, u
}
EXPORT_SYMBOL_GPL(kvm_set_xcr);

-int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
+static int kvm_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
{
- unsigned long old_cr4 = kvm_read_cr4(vcpu);
- unsigned long pdptr_bits = X86_CR4_PGE | X86_CR4_PSE | X86_CR4_PAE |
- X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_PKE;
-
if (cr4 & CR4_RESERVED_BITS)
- return 1;
+ return -EINVAL;

if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVE) && (cr4 & X86_CR4_OSXSAVE))
- return 1;
+ return -EINVAL;

if (!guest_cpuid_has(vcpu, X86_FEATURE_SMEP) && (cr4 & X86_CR4_SMEP))
- return 1;
+ return -EINVAL;

if (!guest_cpuid_has(vcpu, X86_FEATURE_SMAP) && (cr4 & X86_CR4_SMAP))
- return 1;
+ return -EINVAL;

if (!guest_cpuid_has(vcpu, X86_FEATURE_FSGSBASE) && (cr4 & X86_CR4_FSGSBASE))
- return 1;
+ return -EINVAL;

if (!guest_cpuid_has(vcpu, X86_FEATURE_PKU) && (cr4 & X86_CR4_PKE))
- return 1;
+ return -EINVAL;

if (!guest_cpuid_has(vcpu, X86_FEATURE_LA57) && (cr4 & X86_CR4_LA57))
- return 1;
+ return -EINVAL;

if (!guest_cpuid_has(vcpu, X86_FEATURE_UMIP) && (cr4 & X86_CR4_UMIP))
+ return -EINVAL;
+
+ return 0;
+}
+
+int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
+{
+ unsigned long old_cr4 = kvm_read_cr4(vcpu);
+ unsigned long pdptr_bits = X86_CR4_PGE | X86_CR4_PSE | X86_CR4_PAE |
+ X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_PKE;
+
+ if (kvm_valid_cr4(vcpu, cr4))
return 1;

if (is_long_mode(vcpu)) {
@@ -8237,10 +8245,6 @@ EXPORT_SYMBOL_GPL(kvm_task_switch);

static int kvm_valid_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
{
- if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVE) &&
- (sregs->cr4 & X86_CR4_OSXSAVE))
- return -EINVAL;
-
if ((sregs->efer & EFER_LME) && (sregs->cr0 & X86_CR0_PG)) {
/*
* When EFER.LME and CR0.PG are set, the processor is in
@@ -8259,7 +8263,7 @@ static int kvm_valid_sregs(struct kvm_vc
return -EINVAL;
}

- return 0;
+ return kvm_valid_cr4(vcpu, sregs->cr4);
}

static int __set_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)

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