Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit e39d200f authored by Wanpeng Li's avatar Wanpeng Li Committed by Paolo Bonzini
Browse files

KVM: Fix stack-out-of-bounds read in write_mmio 



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: default avatarDmitry Vyukov <dvyukov@google.com>
Reviewed-by: default avatarDarren Kenny <darren.kenny@oracle.com>
Reviewed-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Tested-by: default avatarMarc 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: default avatarWanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent f2981033

arch/x86/kvm/x86.c

+4 −4
Original line number Diff line number Diff line
@@ -4384,7 +4384,7 @@ static int vcpu_mmio_read(struct kvm_vcpu *vcpu, gpa_t addr, int len, void *v) 
					 addr, n, v))

		    && kvm_io_bus_read(vcpu, KVM_MMIO_BUS, addr, n, v))

			break;

		trace_kvm_mmio(KVM_TRACE_MMIO_READ, n, addr, *(u64 *)v);

		trace_kvm_mmio(KVM_TRACE_MMIO_READ, n, addr, v);

		handled += n;

		addr += n;

		len -= n;
@@ -4643,7 +4643,7 @@ static int read_prepare(struct kvm_vcpu *vcpu, void *val, int bytes) 
{

	if (vcpu->mmio_read_completed) {

		trace_kvm_mmio(KVM_TRACE_MMIO_READ, bytes,

			       vcpu->mmio_fragments[0].gpa, *(u64 *)val);

			       vcpu->mmio_fragments[0].gpa, val);

		vcpu->mmio_read_completed = 0;

		return 1;

	}
@@ -4665,14 +4665,14 @@ static int write_emulate(struct kvm_vcpu *vcpu, gpa_t gpa, 


static int write_mmio(struct kvm_vcpu *vcpu, gpa_t gpa, int bytes, void *val)

{

	trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, bytes, gpa, *(u64 *)val);

	trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, bytes, gpa, val);

	return vcpu_mmio_write(vcpu, gpa, bytes, val);

}



static int read_exit_mmio(struct kvm_vcpu *vcpu, gpa_t gpa,

			  void *val, int bytes)

{

	trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, bytes, gpa, 0);

	trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, bytes, gpa, NULL);

	return X86EMUL_IO_NEEDED;

}

include/trace/events/kvm.h

+5 −2
Original line number Diff line number Diff line
@@ -211,7 +211,7 @@ TRACE_EVENT(kvm_ack_irq, 
	{ KVM_TRACE_MMIO_WRITE, "write" }



TRACE_EVENT(kvm_mmio,

	TP_PROTO(int type, int len, u64 gpa, u64 val),

	TP_PROTO(int type, int len, u64 gpa, void *val),

	TP_ARGS(type, len, gpa, val),



	TP_STRUCT__entry(
@@ -225,7 +225,10 @@ TRACE_EVENT(kvm_mmio, 
		__entry->type		= type;

		__entry->len		= len;

		__entry->gpa		= gpa;

		__entry->val		= val;

		__entry->val		= 0;

		if (val)

			memcpy(&__entry->val, val,

			       min_t(u32, sizeof(__entry->val), len));

	),



	TP_printk("mmio %s len %u gpa 0x%llx val 0x%llx",

virt/kvm/arm/mmio.c

+3 −3
Original line number Diff line number Diff line
@@ -112,7 +112,7 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run) 
		}



		trace_kvm_mmio(KVM_TRACE_MMIO_READ, len, run->mmio.phys_addr,

			       data);

			       &data);

		data = vcpu_data_host_to_guest(vcpu, data, len);

		vcpu_set_reg(vcpu, vcpu->arch.mmio_decode.rt, data);

	}
@@ -182,14 +182,14 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run, 
		data = vcpu_data_guest_to_host(vcpu, vcpu_get_reg(vcpu, rt),

					       len);



		trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, len, fault_ipa, data);

		trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, len, fault_ipa, &data);

		kvm_mmio_write_buf(data_buf, len, data);



		ret = kvm_io_bus_write(vcpu, KVM_MMIO_BUS, fault_ipa, len,

				       data_buf);

	} else {

		trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, len,

			       fault_ipa, 0);

			       fault_ipa, NULL);



		ret = kvm_io_bus_read(vcpu, KVM_MMIO_BUS, fault_ipa, len,

				      data_buf);