CVE-2012-4461: kvm: invalid opcode oops on SET_SREGS with OSXSAVE bit set (rhbz 878518 862900)
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Josh Boyer
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From 6d1068b3a98519247d8ba4ec85cd40ac136dbdf9 Mon Sep 17 00:00:00 2001
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From: Petr Matousek <pmatouse@redhat.com>
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Date: Tue, 6 Nov 2012 19:24:07 +0100
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Subject: [PATCH] KVM: x86: invalid opcode oops on SET_SREGS with OSXSAVE bit
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set (CVE-2012-4461)
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On hosts without the XSAVE support unprivileged local user can trigger
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oops similar to the one below by setting X86_CR4_OSXSAVE bit in guest
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cr4 register using KVM_SET_SREGS ioctl and later issuing KVM_RUN
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ioctl.
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invalid opcode: 0000 [#2] SMP
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Modules linked in: tun ip6table_filter ip6_tables ebtable_nat ebtables
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...
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Pid: 24935, comm: zoog_kvm_monito Tainted: G D 3.2.0-3-686-pae
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EIP: 0060:[<f8b9550c>] EFLAGS: 00210246 CPU: 0
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EIP is at kvm_arch_vcpu_ioctl_run+0x92a/0xd13 [kvm]
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EAX: 00000001 EBX: 000f387e ECX: 00000000 EDX: 00000000
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ESI: 00000000 EDI: 00000000 EBP: ef5a0060 ESP: d7c63e70
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DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
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Process zoog_kvm_monito (pid: 24935, ti=d7c62000 task=ed84a0c0
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task.ti=d7c62000)
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Stack:
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00000001 f70a1200 f8b940a9 ef5a0060 00000000 00200202 f8769009 00000000
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ef5a0060 000f387e eda5c020 8722f9c8 00015bae 00000000 ed84a0c0 ed84a0c0
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c12bf02d 0000ae80 ef7f8740 fffffffb f359b740 ef5a0060 f8b85dc1 0000ae80
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Call Trace:
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[<f8b940a9>] ? kvm_arch_vcpu_ioctl_set_sregs+0x2fe/0x308 [kvm]
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...
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[<c12bfb44>] ? syscall_call+0x7/0xb
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Code: 89 e8 e8 14 ee ff ff ba 00 00 04 00 89 e8 e8 98 48 ff ff 85 c0 74
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1e 83 7d 48 00 75 18 8b 85 08 07 00 00 31 c9 8b 95 0c 07 00 00 <0f> 01
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d1 c7 45 48 01 00 00 00 c7 45 1c 01 00 00 00 0f ae f0 89
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EIP: [<f8b9550c>] kvm_arch_vcpu_ioctl_run+0x92a/0xd13 [kvm] SS:ESP
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0068:d7c63e70
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QEMU first retrieves the supported features via KVM_GET_SUPPORTED_CPUID
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and then sets them later. So guest's X86_FEATURE_XSAVE should be masked
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out on hosts without X86_FEATURE_XSAVE, making kvm_set_cr4 with
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X86_CR4_OSXSAVE fail. Userspaces that allow specifying guest cpuid with
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X86_FEATURE_XSAVE even on hosts that do not support it, might be
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susceptible to this attack from inside the guest as well.
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Allow setting X86_CR4_OSXSAVE bit only if host has XSAVE support.
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Signed-off-by: Petr Matousek <pmatouse@redhat.com>
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Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
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---
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arch/x86/kvm/cpuid.h | 3 +++
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arch/x86/kvm/x86.c | 3 +++
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2 files changed, 6 insertions(+)
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diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
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index a10e460..58fc514 100644
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--- a/arch/x86/kvm/cpuid.h
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+++ b/arch/x86/kvm/cpuid.h
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@@ -24,6 +24,9 @@ static inline bool guest_cpuid_has_xsave(struct kvm_vcpu *vcpu)
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{
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struct kvm_cpuid_entry2 *best;
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+ if (!static_cpu_has(X86_FEATURE_XSAVE))
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+ return 0;
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+
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best = kvm_find_cpuid_entry(vcpu, 1, 0);
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return best && (best->ecx & bit(X86_FEATURE_XSAVE));
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}
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diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
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index 224a7e7..4f76417 100644
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--- a/arch/x86/kvm/x86.c
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+++ b/arch/x86/kvm/x86.c
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@@ -5781,6 +5781,9 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
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int pending_vec, max_bits, idx;
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struct desc_ptr dt;
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+ if (!guest_cpuid_has_xsave(vcpu) && (sregs->cr4 & X86_CR4_OSXSAVE))
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+ return -EINVAL;
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+
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dt.size = sregs->idt.limit;
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dt.address = sregs->idt.base;
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kvm_x86_ops->set_idt(vcpu, &dt);
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--
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1.8.0
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@ -54,7 +54,7 @@ Summary: The Linux kernel
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# For non-released -rc kernels, this will be appended after the rcX and
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# gitX tags, so a 3 here would become part of release "0.rcX.gitX.3"
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#
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%global baserelease 3
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%global baserelease 4
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%global fedora_build %{baserelease}
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# base_sublevel is the kernel version we're starting with and patching
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@ -724,6 +724,9 @@ Patch22122: fs-lock-splice_read-and-splice_write-functions.patch
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#rhbz 874791
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Patch22125: Bluetooth-Add-support-for-BCM20702A0.patch
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#rhbz CVE-2012-4461 862900 878518
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Patch21227: KVM-x86-invalid-opcode-oops-on-SET_SREGS-with-OSXSAV.patch
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# END OF PATCH DEFINITIONS
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%endif
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@ -1365,6 +1368,9 @@ ApplyPatch fs-lock-splice_read-and-splice_write-functions.patch
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#rhbz 874791
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ApplyPatch Bluetooth-Add-support-for-BCM20702A0.patch
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#rhbz CVE-2012-4461 862900 878518
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ApplyPatch KVM-x86-invalid-opcode-oops-on-SET_SREGS-with-OSXSAV.patch
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# END OF PATCH APPLICATIONS
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%endif
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@ -2066,6 +2072,7 @@ fi
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%changelog
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* Tue Nov 20 2012 Josh Boyer <jwboyer@redhat.com>
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- CVE-2012-4461: kvm: invalid opcode oops on SET_SREGS with OSXSAVE bit set (rhbz 878518 862900)
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- Add support for BCM20702A0 (rhbz 874791)
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* Mon Nov 19 2012 Josh Boyer <jwboyer@redhat.com>
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