From: Wanpeng Li <[email protected]>
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: [email protected]
Cc: [email protected]
Signed-off-by: Wanpeng Li <[email protected]>
---
arch/x86/kvm/x86.c | 39 ++++++++++++++++++++++++---------------
1 file changed, 24 insertions(+), 15 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f7cfd8e..cafb4d4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -884,34 +884,42 @@ int kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
}
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;
-
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 (cr4 & CR4_RESERVED_BITS)
+ return 1;
+
+ if (kvm_valid_cr4(vcpu, cr4))
return 1;
if (is_long_mode(vcpu)) {
@@ -8675,7 +8683,8 @@ static int __set_sregs(struct kvm_vcpu *vcpu, struct
kvm_sregs *sregs)
struct desc_ptr dt;
int ret = -EINVAL;
- if (kvm_valid_sregs(vcpu, sregs))
+ if (kvm_valid_sregs(vcpu, sregs) ||
+ kvm_valid_cr4(vcpu, sregs->cr4))
goto out;
apic_base_msr.data = sregs->apic_base;
--
2.7.4
