On Mon, Oct 14, 2019 at 11:08:24AM +0200, Vitaly Kuznetsov wrote:

bugzilla-daemon@bugzilla.kernel.org writes:

...

https://bugzilla.kernel.org/show_bug.cgi?id=205171

        Bug ID: 205171
       Summary: kernel panic during windows 10pro start
       Product: Virtualization
       Version: unspecified
Kernel Version: 4.19.74 and higher
      Hardware: All
            OS: Linux
          Tree: Mainline
        Status: NEW
      Severity: normal
      Priority: P1
     Component: kvm
      Assignee: virtualization_kvm@kernel-bugs.osdl.org
      Reporter: dront78@gmail.com
    Regression: No

works fine on 4.19.73

[ 5829.948945] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 [ 5829.948951] PGD 0 P4D 0 [ 5829.948954] Oops: 0002 [#1] SMP NOPTI [ 5829.948957] CPU: 3 PID: 1699 Comm: CPU 0/KVM Tainted: G OE 4.19.78-2-lts #1 [ 5829.948958] Hardware name: Micro-Star International Co., Ltd. GE62 6QF/MS-16J4, BIOS E16J4IMS.117 01/18/2018 [ 5829.948989] RIP: 0010:kvm_write_guest_virt_system+0x1e/0x40 [kvm]

It seems 4.19 stable backport is broken, upstream commit f7eea636c3d50 has:

@@ -4588,7 +4589,8 @@ static int handle_vmread(struct kvm_vcpu *vcpu) vmx_instruction_info, true, len, &gva)) return 1; /* _system ok, nested_vmx_check_permission has verified cpl=0 */

•           kvm_write_guest_virt_system(vcpu, gva, &field_value, len, NULL);
  

•           if (kvm_write_guest_virt_system(vcpu, gva, &field_value, len, &e))
  

•                   kvm_inject_page_fault(vcpu, &e);
    }
  
  

and it's 4.19 counterpart (73c31bd92039):

@@ -8798,8 +8799,10 @@ static int handle_vmread(struct kvm_vcpu *vcpu) vmx_instruction_info, true, &gva)) return 1; /* _system ok, nested_vmx_check_permission has verified cpl=0 */

•           kvm_write_guest_virt_system(vcpu, gva, &field_value,
  

•                                       (is_long_mode(vcpu) ? 8 : 4), NULL);
  

•           if (kvm_write_guest_virt_system(vcpu, gva, &field_value,
  

•                                           (is_long_mode(vcpu) ? 8 : 4),
  

•                                           NULL))
  

•                   kvm_inject_page_fault(vcpu, &e);
    }
  

(note the last argument to kvm_write_guest_virt_system() - it's NULL instead of &e.

And v4.19.74 has 6e60900cfa3e (541ab2aeb282 upstream):

@@ -5016,6 +5016,13 @@ int kvm_write_guest_virt_system(struct kvm_vcpu *vcpu, gva_t addr, void *val, /* kvm_write_guest_virt_system can pull in tons of pages. */ vcpu->arch.l1tf_flush_l1d = true;

•   /*
  

•    * FIXME: this should call handle_emulation_failure if X86EMUL_IO_NEEDED
  

•    * is returned, but our callers are not ready for that and they blindly
  

•    * call kvm_inject_page_fault.  Ensure that they at least do not leak
  

•    * uninitialized kernel stack memory into cr2 and error code.
  

•    */
  

•   memset(exception, 0, sizeof(*exception));
    return kvm_write_guest_virt_helper(addr, val, bytes, vcpu,
                                       PFERR_WRITE_MASK, exception);
  

}

This all results in memset(NULL). (also, 6e60900cfa3e should come *after* f7eea636c3d50 and not before but oh well..)

The following will likely fix the problem (untested):

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index e83f4f6bfdac..d3a900a4fa0e 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -8801,7 +8801,7 @@ static int handle_vmread(struct kvm_vcpu *vcpu) /* _system ok, nested_vmx_check_permission has verified cpl=0 */ if (kvm_write_guest_virt_system(vcpu, gva, &field_value, (is_long_mode(vcpu) ? 8 : 4),

•                                           NULL))
  

•                                           &e))
                    kvm_inject_page_fault(vcpu, &e);
    }
  
  

I can send a patch to stable@ if needed.

A patch was already sent, and is included in the 4.19.79 and 4.14.149 kernel releases, and will be part of the next 4.9.y and 4.4.y kernel releases that happen later this week.

thanks,

greg k-h