From: Wanpeng Li wanpengli@tencent.com
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 --- 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;