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?
thanks,
greg k-h