* [PATCH] KVM: x86: Fully initialize 'struct kvm_lapic_irq' in kvm_pv_kick_cpu_op()
@ 2022-06-28 13:30 Vitaly Kuznetsov
2022-07-07 17:34 ` Sean Christopherson
0 siblings, 1 reply; 3+ messages in thread
From: Vitaly Kuznetsov @ 2022-06-28 13:30 UTC (permalink / raw)
To: kvm, Paolo Bonzini
Cc: Sean Christopherson, Wanpeng Li, Jim Mattson, linux-hyperv, linux-kernel
'vector' and 'trig_mode' fields of 'struct kvm_lapic_irq' are left
uninitialized in kvm_pv_kick_cpu_op(). While these fields are normally
not needed for APIC_DM_REMRD, they're still referenced by
__apic_accept_irq() for trace_kvm_apic_accept_irq(). Fully initialize
the structure to avoid consuming random stack memory.
Fixes: a183b638b61c ("KVM: x86: make apic_accept_irq tracepoint more generic")
Reported-by: syzbot+d6caa905917d353f0d07@syzkaller.appspotmail.com
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/kvm/x86.c | 18 ++++++++++--------
1 file changed, 10 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 567d13405445..8a98608dad4f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9340,15 +9340,17 @@ static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr,
*/
static void kvm_pv_kick_cpu_op(struct kvm *kvm, int apicid)
{
- struct kvm_lapic_irq lapic_irq;
-
- lapic_irq.shorthand = APIC_DEST_NOSHORT;
- lapic_irq.dest_mode = APIC_DEST_PHYSICAL;
- lapic_irq.level = 0;
- lapic_irq.dest_id = apicid;
- lapic_irq.msi_redir_hint = false;
+ struct kvm_lapic_irq lapic_irq = {
+ .vector = 0,
+ .delivery_mode = APIC_DM_REMRD,
+ .dest_mode = APIC_DEST_PHYSICAL,
+ .level = false,
+ .trig_mode = 0,
+ .shorthand = APIC_DEST_NOSHORT,
+ .dest_id = apicid,
+ .msi_redir_hint = false
+ };
- lapic_irq.delivery_mode = APIC_DM_REMRD;
kvm_irq_delivery_to_apic(kvm, NULL, &lapic_irq, NULL);
}
--
2.35.3
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: x86: Fully initialize 'struct kvm_lapic_irq' in kvm_pv_kick_cpu_op()
2022-06-28 13:30 [PATCH] KVM: x86: Fully initialize 'struct kvm_lapic_irq' in kvm_pv_kick_cpu_op() Vitaly Kuznetsov
@ 2022-07-07 17:34 ` Sean Christopherson
2022-07-08 12:44 ` Vitaly Kuznetsov
0 siblings, 1 reply; 3+ messages in thread
From: Sean Christopherson @ 2022-07-07 17:34 UTC (permalink / raw)
To: Vitaly Kuznetsov
Cc: kvm, Paolo Bonzini, Wanpeng Li, Jim Mattson, linux-hyperv, linux-kernel
On Tue, Jun 28, 2022, Vitaly Kuznetsov wrote:
> 'vector' and 'trig_mode' fields of 'struct kvm_lapic_irq' are left
> uninitialized in kvm_pv_kick_cpu_op(). While these fields are normally
> not needed for APIC_DM_REMRD, they're still referenced by
> __apic_accept_irq() for trace_kvm_apic_accept_irq(). Fully initialize
> the structure to avoid consuming random stack memory.
>
> Fixes: a183b638b61c ("KVM: x86: make apic_accept_irq tracepoint more generic")
> Reported-by: syzbot+d6caa905917d353f0d07@syzkaller.appspotmail.com
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> arch/x86/kvm/x86.c | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 567d13405445..8a98608dad4f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9340,15 +9340,17 @@ static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr,
> */
> static void kvm_pv_kick_cpu_op(struct kvm *kvm, int apicid)
> {
> - struct kvm_lapic_irq lapic_irq;
> -
> - lapic_irq.shorthand = APIC_DEST_NOSHORT;
> - lapic_irq.dest_mode = APIC_DEST_PHYSICAL;
> - lapic_irq.level = 0;
> - lapic_irq.dest_id = apicid;
> - lapic_irq.msi_redir_hint = false;
> + struct kvm_lapic_irq lapic_irq = {
> + .vector = 0,
> + .delivery_mode = APIC_DM_REMRD,
> + .dest_mode = APIC_DEST_PHYSICAL,
> + .level = false,
> + .trig_mode = 0,
> + .shorthand = APIC_DEST_NOSHORT,
> + .dest_id = apicid,
> + .msi_redir_hint = false
> + };
What if we rely on the compiler to zero-initialize omitted fields? E.g.
/*
* All other fields are unused for APIC_DM_REMRD, but may be consumed by
* common code, e.g. for tracing. Defer initialization to the compiler.
*/
struct kvm_lapic_irq lapic_irq = {
.delivery_mode = APIC_DM_REMRD,
.dest_mode = APIC_DEST_PHYSICAL,
.shorthand = APIC_DEST_NOSHORT,
.dest_id = apicid,
};
KVM doesn't actually care about the vector, level, trig_mode, etc... for its magic
magic DM_REMRD, i.e. using 0/false is completely arbitrary.
>
> - lapic_irq.delivery_mode = APIC_DM_REMRD;
> kvm_irq_delivery_to_apic(kvm, NULL, &lapic_irq, NULL);
> }
>
> --
> 2.35.3
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: x86: Fully initialize 'struct kvm_lapic_irq' in kvm_pv_kick_cpu_op()
2022-07-07 17:34 ` Sean Christopherson
@ 2022-07-08 12:44 ` Vitaly Kuznetsov
0 siblings, 0 replies; 3+ messages in thread
From: Vitaly Kuznetsov @ 2022-07-08 12:44 UTC (permalink / raw)
To: Sean Christopherson
Cc: kvm, Paolo Bonzini, Wanpeng Li, Jim Mattson, linux-hyperv, linux-kernel
Sean Christopherson <seanjc@google.com> writes:
> On Tue, Jun 28, 2022, Vitaly Kuznetsov wrote:
>> 'vector' and 'trig_mode' fields of 'struct kvm_lapic_irq' are left
>> uninitialized in kvm_pv_kick_cpu_op(). While these fields are normally
>> not needed for APIC_DM_REMRD, they're still referenced by
>> __apic_accept_irq() for trace_kvm_apic_accept_irq(). Fully initialize
>> the structure to avoid consuming random stack memory.
>>
>> Fixes: a183b638b61c ("KVM: x86: make apic_accept_irq tracepoint more generic")
>> Reported-by: syzbot+d6caa905917d353f0d07@syzkaller.appspotmail.com
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>> arch/x86/kvm/x86.c | 18 ++++++++++--------
>> 1 file changed, 10 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 567d13405445..8a98608dad4f 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -9340,15 +9340,17 @@ static int kvm_pv_clock_pairing(struct kvm_vcpu *vcpu, gpa_t paddr,
>> */
>> static void kvm_pv_kick_cpu_op(struct kvm *kvm, int apicid)
>> {
>> - struct kvm_lapic_irq lapic_irq;
>> -
>> - lapic_irq.shorthand = APIC_DEST_NOSHORT;
>> - lapic_irq.dest_mode = APIC_DEST_PHYSICAL;
>> - lapic_irq.level = 0;
>> - lapic_irq.dest_id = apicid;
>> - lapic_irq.msi_redir_hint = false;
>> + struct kvm_lapic_irq lapic_irq = {
>> + .vector = 0,
>> + .delivery_mode = APIC_DM_REMRD,
>> + .dest_mode = APIC_DEST_PHYSICAL,
>> + .level = false,
>> + .trig_mode = 0,
>> + .shorthand = APIC_DEST_NOSHORT,
>> + .dest_id = apicid,
>> + .msi_redir_hint = false
>> + };
>
> What if we rely on the compiler to zero-initialize omitted fields? E.g.
>
> /*
> * All other fields are unused for APIC_DM_REMRD, but may be consumed by
> * common code, e.g. for tracing. Defer initialization to the compiler.
> */
> struct kvm_lapic_irq lapic_irq = {
> .delivery_mode = APIC_DM_REMRD,
> .dest_mode = APIC_DEST_PHYSICAL,
> .shorthand = APIC_DEST_NOSHORT,
> .dest_id = apicid,
> };
>
> KVM doesn't actually care about the vector, level, trig_mode, etc... for its magic
> magic DM_REMRD, i.e. using 0/false is completely arbitrary.
Honestly, I just always forget whether zero-initializing of omitted
fields is a de-facto or de-jure standard. We don't care much whether
these fields are zero of not but some random values in tracing may
confuse an unprepared reader.
I'll send v2 with your amendment.
>
>>
>> - lapic_irq.delivery_mode = APIC_DM_REMRD;
>> kvm_irq_delivery_to_apic(kvm, NULL, &lapic_irq, NULL);
>> }
>>
>> --
>> 2.35.3
>>
>
--
Vitaly
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2022-07-08 12:44 UTC | newest]
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2022-06-28 13:30 [PATCH] KVM: x86: Fully initialize 'struct kvm_lapic_irq' in kvm_pv_kick_cpu_op() Vitaly Kuznetsov
2022-07-07 17:34 ` Sean Christopherson
2022-07-08 12:44 ` Vitaly Kuznetsov
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