Patch "KVM: x86: Fix load damaged SSEx MXCSR register" has been added to the 4.9-stable tree

Patch "KVM: x86: Fix load damaged SSEx MXCSR register" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    KVM: x86: Fix load damaged SSEx MXCSR register

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-x86-fix-load-damaged-ssex-mxcsr-register.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From a575813bfe4bc15aba511a5e91e61d242bff8b9d Mon Sep 17 00:00:00 2001
From: Wanpeng Li <wanpeng.li@hotmail.com>
Date: Thu, 11 May 2017 02:58:55 -0700
Subject: KVM: x86: Fix load damaged SSEx MXCSR register
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: Wanpeng Li <wanpeng.li@hotmail.com>

commit a575813bfe4bc15aba511a5e91e61d242bff8b9d upstream.

Reported by syzkaller:

   BUG: unable to handle kernel paging request at ffffffffc07f6a2e
   IP: report_bug+0x94/0x120
   PGD 348e12067
   P4D 348e12067
   PUD 348e14067
   PMD 3cbd84067
   PTE 80000003f7e87161

   Oops: 0003 [#1] SMP
   CPU: 2 PID: 7091 Comm: kvm_load_guest_ Tainted: G           OE   4.11.0+ #8
   task: ffff92fdfb525400 task.stack: ffffbda6c3d04000
   RIP: 0010:report_bug+0x94/0x120
   RSP: 0018:ffffbda6c3d07b20 EFLAGS: 00010202
    do_trap+0x156/0x170
    do_error_trap+0xa3/0x170
    ? kvm_load_guest_fpu.part.175+0x12a/0x170 [kvm]
    ? mark_held_locks+0x79/0xa0
    ? retint_kernel+0x10/0x10
    ? trace_hardirqs_off_thunk+0x1a/0x1c
    do_invalid_op+0x20/0x30
    invalid_op+0x1e/0x30
   RIP: 0010:kvm_load_guest_fpu.part.175+0x12a/0x170 [kvm]
    ? kvm_load_guest_fpu.part.175+0x1c/0x170 [kvm]
    kvm_arch_vcpu_ioctl_run+0xed6/0x1b70 [kvm]
    kvm_vcpu_ioctl+0x384/0x780 [kvm]
    ? kvm_vcpu_ioctl+0x384/0x780 [kvm]
    ? sched_clock+0x13/0x20
    ? __do_page_fault+0x2a0/0x550
    do_vfs_ioctl+0xa4/0x700
    ? up_read+0x1f/0x40
    ? __do_page_fault+0x2a0/0x550
    SyS_ioctl+0x79/0x90
    entry_SYSCALL_64_fastpath+0x23/0xc2

SDM mentioned that "The MXCSR has several reserved bits, and attempting to write
a 1 to any of these bits will cause a general-protection exception(#GP) to be
generated". The syzkaller forks' testcase overrides xsave area w/ random values
and steps on the reserved bits of MXCSR register. The damaged MXCSR register
values of guest will be restored to SSEx MXCSR register before vmentry. This
patch fixes it by catching userspace override MXCSR register reserved bits w/
random values and bails out immediately.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/kernel/fpu/init.c |    1 +
 arch/x86/kvm/x86.c         |    9 +++++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -101,6 +101,7 @@ static void fpu__init_system_early_gener
  * Boot time FPU feature detection code:
  */
 unsigned int mxcsr_feature_mask __read_mostly = 0xffffffffu;
+EXPORT_SYMBOL_GPL(mxcsr_feature_mask);
 
 static void __init fpu__init_system_mxcsr(void)
 {
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3231,11 +3231,14 @@ static void kvm_vcpu_ioctl_x86_get_xsave
 	}
 }
 
+#define XSAVE_MXCSR_OFFSET 24
+
 static int kvm_vcpu_ioctl_x86_set_xsave(struct kvm_vcpu *vcpu,
 					struct kvm_xsave *guest_xsave)
 {
 	u64 xstate_bv =
 		*(u64 *)&guest_xsave->region[XSAVE_HDR_OFFSET / sizeof(u32)];
+	u32 mxcsr = *(u32 *)&guest_xsave->region[XSAVE_MXCSR_OFFSET / sizeof(u32)];
 
 	if (boot_cpu_has(X86_FEATURE_XSAVE)) {
 		/*
@@ -3243,11 +3246,13 @@ static int kvm_vcpu_ioctl_x86_set_xsave(
 		 * CPUID leaf 0xD, index 0, EDX:EAX.  This is for compatibility
 		 * with old userspace.
 		 */
-		if (xstate_bv & ~kvm_supported_xcr0())
+		if (xstate_bv & ~kvm_supported_xcr0() ||
+			mxcsr & ~mxcsr_feature_mask)
 			return -EINVAL;
 		load_xsave(vcpu, (u8 *)guest_xsave->region);
 	} else {
-		if (xstate_bv & ~XFEATURE_MASK_FPSSE)
+		if (xstate_bv & ~XFEATURE_MASK_FPSSE ||
+			mxcsr & ~mxcsr_feature_mask)
 			return -EINVAL;
 		memcpy(&vcpu->arch.guest_fpu.state.fxsave,
 			guest_xsave->region, sizeof(struct fxregs_state));


Patches currently in stable-queue which might be from wanpeng.li@hotmail.com are

queue-4.9/kvm-x86-fix-potential-preemption-when-get-the-current-kvmclock-timestamp.patch
queue-4.9/kvm-x86-fix-load-damaged-ssex-mxcsr-register.patch
queue-4.9/kvm-x86-fix-read-out-of-bounds-vulnerability-in-kvm-pio-emulation.patch