Re: [PATCH v4] KVM: Fix stack-out-of-bounds read in write_mmio
From: Darren Kenny
Date: Fri Dec 15 2017 - 05:17:19 EST
Code-wise, that looks good to me now. I also don't have ARM handy to
validate though - but it looks correct.
Reviewed-by: Darren Kenny <darren.kenny@xxxxxxxxxx>
Thanks,
Darren.
On Thu, Dec 14, 2017 at 05:40:50PM -0800, Wanpeng Li wrote:
From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
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
can result in stack-out-of-bounds read due to access the extra 5 bytes.
This patch fixes it by just accessing the bytes which we operates 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@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
---
v3 -> v4:
* fix the arm tracepoint
v2 -> v3:
* fix sparse warning
v1 -> v2:
* do the memcpy in kvm_mmio tracepoint
arch/x86/kvm/x86.c | 8 ++++----
include/trace/events/kvm.h | 6 ++++--
virt/kvm/arm/mmio.c | 6 +++---
3 files changed, 11 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0f82e2c..c7071e7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4456,7 +4456,7 @@ 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;
@@ -4715,7 +4715,7 @@ 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;
}
@@ -4737,14 +4737,14 @@ 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;
}
diff --git a/include/trace/events/kvm.h b/include/trace/events/kvm.h
index e4b0b8e..dfd2170 100644
--- a/include/trace/events/kvm.h
+++ b/include/trace/events/kvm.h
@@ -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 +225,9 @@ 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(8, len));
),
TP_printk("mmio %s len %u gpa 0x%llx val 0x%llx",
diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
index b6e715f..dac7ceb 100644
--- a/virt/kvm/arm/mmio.c
+++ b/virt/kvm/arm/mmio.c
@@ -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);
--
2.7.4