2.6.32-longterm review patch. If anyone has any objections, please let me know. ------------------ OSXSAVE bit set (CVE-2012-4461) From: Petr Matousek <pmatouse@xxxxxxxxxx> commit 6d1068b3a98519247d8ba4ec85cd40ac136dbdf9 upstream. On hosts without the XSAVE support unprivileged local user can trigger oops similar to the one below by setting X86_CR4_OSXSAVE bit in guest cr4 register using KVM_SET_SREGS ioctl and later issuing KVM_RUN ioctl. invalid opcode: 0000 [#2] SMP Modules linked in: tun ip6table_filter ip6_tables ebtable_nat ebtables ... Pid: 24935, comm: zoog_kvm_monito Tainted: G D 3.2.0-3-686-pae EIP: 0060:[<f8b9550c>] EFLAGS: 00210246 CPU: 0 EIP is at kvm_arch_vcpu_ioctl_run+0x92a/0xd13 [kvm] EAX: 00000001 EBX: 000f387e ECX: 00000000 EDX: 00000000 ESI: 00000000 EDI: 00000000 EBP: ef5a0060 ESP: d7c63e70 DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 Process zoog_kvm_monito (pid: 24935, ti=d7c62000 task=ed84a0c0 task.ti=d7c62000) Stack: 00000001 f70a1200 f8b940a9 ef5a0060 00000000 00200202 f8769009 00000000 ef5a0060 000f387e eda5c020 8722f9c8 00015bae 00000000 ed84a0c0 ed84a0c0 c12bf02d 0000ae80 ef7f8740 fffffffb f359b740 ef5a0060 f8b85dc1 0000ae80 Call Trace: [<f8b940a9>] ? kvm_arch_vcpu_ioctl_set_sregs+0x2fe/0x308 [kvm] ... [<c12bfb44>] ? syscall_call+0x7/0xb Code: 89 e8 e8 14 ee ff ff ba 00 00 04 00 89 e8 e8 98 48 ff ff 85 c0 74 1e 83 7d 48 00 75 18 8b 85 08 07 00 00 31 c9 8b 95 0c 07 00 00 <0f> 01 d1 c7 45 48 01 00 00 00 c7 45 1c 01 00 00 00 0f ae f0 89 EIP: [<f8b9550c>] kvm_arch_vcpu_ioctl_run+0x92a/0xd13 [kvm] SS:ESP 0068:d7c63e70 QEMU first retrieves the supported features via KVM_GET_SUPPORTED_CPUID and then sets them later. So guest's X86_FEATURE_XSAVE should be masked out on hosts without X86_FEATURE_XSAVE, making kvm_set_cr4 with X86_CR4_OSXSAVE fail. Userspaces that allow specifying guest cpuid with X86_FEATURE_XSAVE even on hosts that do not support it, might be susceptible to this attack from inside the guest as well. Allow setting X86_CR4_OSXSAVE bit only if host has XSAVE support. Signed-off-by: Petr Matousek <pmatouse@xxxxxxxxxx> Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx> [bwh: Backported to 2.6.32: XSAVE is not supported at all, so always deny setting OSXSAVE] Signed-off-by: Willy Tarreau <w@xxxxxx> --- arch/x86/kvm/x86.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 79905f2..ec9728f 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4719,6 +4719,9 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu, int pending_vec, max_bits; struct descriptor_table dt; + if (sregs->cr4 & X86_CR4_OSXSAVE) + return -EINVAL; + vcpu_load(vcpu); dt.limit = sregs->idt.limit; -- 1.7.12.2.21.g234cd45.dirty -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html