[SRU][PATCH 1/1] KVM: X86: Fix scan ioapic use-before-initialization

[Seth Forshee]

On Tue, Dec 04, 2018 at 12:14:08PM +0100, Juerg Haefliger wrote:
> On Mon,  3 Dec 2018 21:22:38 -0500
> Khalid Elmously <khalid.elmously at canonical.com> wrote:
> 
> > From: Wanpeng Li <wanpengli at tencent.com>
> > 
> > CVE-2018-19407
> > 
> > Reported by syzkaller:
> > 
> >  BUG: unable to handle kernel NULL pointer dereference at 00000000000001c8
> >  PGD 80000003ec4da067 P4D 80000003ec4da067 PUD 3f7bfa067 PMD 0
> >  Oops: 0000 [#1] PREEMPT SMP PTI
> >  CPU: 7 PID: 5059 Comm: debug Tainted: G           OE     4.19.0-rc5 #16
> >  RIP: 0010:__lock_acquire+0x1a6/0x1990
> >  Call Trace:
> >   lock_acquire+0xdb/0x210
> >   _raw_spin_lock+0x38/0x70
> >   kvm_ioapic_scan_entry+0x3e/0x110 [kvm]
> >   vcpu_enter_guest+0x167e/0x1910 [kvm]
> >   kvm_arch_vcpu_ioctl_run+0x35c/0x610 [kvm]
> >   kvm_vcpu_ioctl+0x3e9/0x6d0 [kvm]
> >   do_vfs_ioctl+0xa5/0x690
> >   ksys_ioctl+0x6d/0x80
> >   __x64_sys_ioctl+0x1a/0x20
> >   do_syscall_64+0x83/0x6e0
> >   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > 
> > The reason is that the testcase writes hyperv synic HV_X64_MSR_SINT6 msr
> > and triggers scan ioapic logic to load synic vectors into EOI exit bitmap.
> > However, irqchip is not initialized by this simple testcase, ioapic/apic
> > objects should not be accessed.
> > This can be triggered by the following program:
> > 
> >     #define _GNU_SOURCE
> > 
> >     #include <endian.h>
> >     #include <stdint.h>
> >     #include <stdio.h>
> >     #include <stdlib.h>
> >     #include <string.h>
> >     #include <sys/syscall.h>
> >     #include <sys/types.h>
> >     #include <unistd.h>
> > 
> >     uint64_t r[3] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff};
> > 
> >     int main(void)
> >     {
> >     	syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0);
> >     	long res = 0;
> >     	memcpy((void*)0x20000040, "/dev/kvm", 9);
> >     	res = syscall(__NR_openat, 0xffffffffffffff9c, 0x20000040, 0, 0);
> >     	if (res != -1)
> >     		r[0] = res;
> >     	res = syscall(__NR_ioctl, r[0], 0xae01, 0);
> >     	if (res != -1)
> >     		r[1] = res;
> >     	res = syscall(__NR_ioctl, r[1], 0xae41, 0);
> >     	if (res != -1)
> >     		r[2] = res;
> >     	memcpy(
> >     			(void*)0x20000080,
> >     			"\x01\x00\x00\x00\x00\x5b\x61\xbb\x96\x00\x00\x40\x00\x00\x00\x00\x01\x00"
> >     			"\x08\x00\x00\x00\x00\x00\x0b\x77\xd1\x78\x4d\xd8\x3a\xed\xb1\x5c\x2e\x43"
> >     			"\xaa\x43\x39\xd6\xff\xf5\xf0\xa8\x98\xf2\x3e\x37\x29\x89\xde\x88\xc6\x33"
> >     			"\xfc\x2a\xdb\xb7\xe1\x4c\xac\x28\x61\x7b\x9c\xa9\xbc\x0d\xa0\x63\xfe\xfe"
> >     			"\xe8\x75\xde\xdd\x19\x38\xdc\x34\xf5\xec\x05\xfd\xeb\x5d\xed\x2e\xaf\x22"
> >     			"\xfa\xab\xb7\xe4\x42\x67\xd0\xaf\x06\x1c\x6a\x35\x67\x10\x55\xcb",
> >     			106);
> >     	syscall(__NR_ioctl, r[2], 0x4008ae89, 0x20000080);
> >     	syscall(__NR_ioctl, r[2], 0xae80, 0);
> >     	return 0;
> >     }
> > 
> > This patch fixes it by bailing out scan ioapic if ioapic is not initialized in
> > kernel.
> > 
> > Reported-by: Wei Wu <ww9210 at gmail.com>
> > Cc: Paolo Bonzini <pbonzini at redhat.com>
> > Cc: Radim Krčmář <rkrcmar at redhat.com>
> > Cc: Wei Wu <ww9210 at gmail.com>
> > Signed-off-by: Wanpeng Li <wanpengli at tencent.com>
> > Cc: stable at vger.kernel.org
> > Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
> 
> Empty line here please.

Um, why? This has never been a requirement, and it's not what is
produced by 'git cherry-pick -x'. I personally don't want to have to go
in and hand-edit the commit message to add a blank line here every time
I cherry pick a patch.