Re: [PATCH] KVM: Fix stack-out-of-bounds read in write_mmio

[Greg KH <greg@kroah.com>]

On Wed, Jan 10, 2018 at 02:06:38PM +0100, Paolo Bonzini wrote:
> On 10/01/2018 13:14, Greg KH wrote:
> > On Tue, Jan 09, 2018 at 07:24:27AM -0800, sawlani@google.com wrote:
> >> From: Pradeep Sawlani <sawlani@google.com>
> >>
> >> commit e39d200fa5bf5b94a0948db0dae44c1b73b84a56 upstream.
> >>
> >> Reported by syzkaller:
> >>
> >>   BUG: KASAN: stack-out-of-bounds in write_mmio+0x11e/0x270 [kvm]
> >>   Read of size 8 at addr ffff8803259df7f8 by task syz-executor/32298
> >>
> >>   CPU: 6 PID: 32298 Comm: syz-executor Tainted: G           OE    4.15.0-rc2+ #18
> >>   Hardware name: LENOVO ThinkCentre M8500t-N000/SHARKBAY, BIOS FBKTC1AUS 02/16/2016
> >>   Call Trace:
> >>    dump_stack+0xab/0xe1
> >>    print_address_description+0x6b/0x290
> >>    kasan_report+0x28a/0x370
> >>    write_mmio+0x11e/0x270 [kvm]
> >>    emulator_read_write_onepage+0x311/0x600 [kvm]
> >>    emulator_read_write+0xef/0x240 [kvm]
> >>    emulator_fix_hypercall+0x105/0x150 [kvm]
> >>    em_hypercall+0x2b/0x80 [kvm]
> >>    x86_emulate_insn+0x2b1/0x1640 [kvm]
> >>    x86_emulate_instruction+0x39a/0xb90 [kvm]
> >>    handle_exception+0x1b4/0x4d0 [kvm_intel]
> >>    vcpu_enter_guest+0x15a0/0x2640 [kvm]
> >>    kvm_arch_vcpu_ioctl_run+0x549/0x7d0 [kvm]
> >>    kvm_vcpu_ioctl+0x479/0x880 [kvm]
> >>    do_vfs_ioctl+0x142/0x9a0
> >>    SyS_ioctl+0x74/0x80
> >>    entry_SYSCALL_64_fastpath+0x23/0x9a
> >>
> >> The path of patched vmmcall will patch 3 bytes opcode 0F 01 C1(vmcall)
> >> to the guest memory, however, write_mmio tracepoint always prints 8 bytes
> >> through *(u64 *)val since kvm splits the mmio access into 8 bytes. This
> >> leaks 5 bytes from the kernel stack (CVE-2017-17741).  This patch fixes
> >> it by just accessing the bytes which we operate on.
> >>
> >> Before patch:
> >>
> >> syz-executor-5567  [007] .... 51370.561696: kvm_mmio: mmio write len 3 gpa 0x10 val 0x1ffff10077c1010f
> >>
> >> After patch:
> >>
> >> syz-executor-13416 [002] .... 51302.299573: kvm_mmio: mmio write len 3 gpa 0x10 val 0xc1010f
> >>
> >> Reported-by: Dmitry Vyukov <dvyukov@google.com>
> >> Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
> >> Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
> >> Tested-by: Marc Zyngier <marc.zyngier@arm.com>
> >> Cc: Paolo Bonzini <pbonzini@redhat.com>
> >> Cc: Radim Krčmář <rkrcmar@redhat.com>
> >> Cc: Marc Zyngier <marc.zyngier@arm.com>
> >> Cc: Christoffer Dall <christoffer.dall@linaro.org>
> >> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> >> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> >> Signed-off-by: Pradeep Sawlani <sawlani@google.com>
> >> ---
> >>  arch/arm/kvm/mmio.c        | 6 +++---
> >>  arch/x86/kvm/x86.c         | 8 ++++----
> >>  include/trace/events/kvm.h | 7 +++++--
> >>  3 files changed, 12 insertions(+), 9 deletions(-)
> > 
> > What stable kernel(s) do you want this applied to?
> 
> This is a kernel memory leak, I think it only really matters in kernels
> that have unprivileged eBPF.  But that went in for 4.4, so all of
> 4.4/4.9/4.14.

Ok, thanks.  Looks like someone else just asked for this as well, and I
had already queued it up a few hours ago :)

greg k-h