From: Wanpeng Li <[email protected]>
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 <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Radim Krčmář <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
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 ++++--
2 files changed, 8 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index daa1918..315ff2c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4457,7 +4457,7 @@ 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;
@@ -4716,7 +4716,7 @@ 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;
}
@@ -4738,14 +4738,14 @@ 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",
--
2.7.4
Hi,
I'm wondering about the change to trace_kvm_mmio() here, since it
doesn't appear to be changing the use of it in
virt/kvm/arm/mmio.c, e.g:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/virt/kvm/arm/mmio.c#n114
which seems to be still using it with a data value rather than a
pointer like you've changed it to in the header.
Should that also be modified to match? As it is, it would appear to
cause a compilation error on ARM (though I've not confirmed).
Thanks,
Darren.
On Thu, Dec 14, 2017 at 05:56:58AM -0800, Wanpeng Li wrote:
>From: Wanpeng Li <[email protected]>
>
>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 <[email protected]>
>Cc: Paolo Bonzini <[email protected]>
>Cc: Radim Krčmář <[email protected]>
>Signed-off-by: Wanpeng Li <[email protected]>
>---
>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 ++++--
> 2 files changed, 8 insertions(+), 6 deletions(-)
>
>diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>index daa1918..315ff2c 100644
>--- a/arch/x86/kvm/x86.c
>+++ b/arch/x86/kvm/x86.c
>@@ -4457,7 +4457,7 @@ 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;
>@@ -4716,7 +4716,7 @@ 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;
> }
>@@ -4738,14 +4738,14 @@ 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",
>--
>2.7.4
>
2017-12-14 22:18 GMT+08:00 Darren Kenny <[email protected]>:
> Hi,
>
> I'm wondering about the change to trace_kvm_mmio() here, since it
> doesn't appear to be changing the use of it in
> virt/kvm/arm/mmio.c, e.g:
>
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/virt/kvm/arm/mmio.c#n114
>
> which seems to be still using it with a data value rather than a
> pointer like you've changed it to in the header.
>
> Should that also be modified to match? As it is, it would appear to
> cause a compilation error on ARM (though I've not confirmed).
Yeah, fix it in v4, https://lkml.org/lkml/2017/12/14/954 however, I
don't have an ARM environment to compile it though the change is very
simple.
Regards,
Wanpeng Li