* Re: [patch RFC] kvm, cpuid: silence a buffer overflow warning
@ 2014-02-20 13:07 ` Paolo Bonzini
0 siblings, 0 replies; 10+ messages in thread
From: Paolo Bonzini @ 2014-02-20 13:07 UTC (permalink / raw)
To: Dan Carpenter, Gleb Natapov
Cc: Thomas Gleixner, Ingo Molnar, H. Peter Anvin, x86, kvm,
kernel-janitors
Il 20/02/2014 13:34, Dan Carpenter ha scritto:
> This seems like a harmless off by one overflow if "i" is the last
> element in the vcpu->arch.cpuid_entries[] array.
>
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> Not tested. I always wonder if it's worth fixing these or if it's worth
> reporting them? Either of those seem like a lot of work for something
> harmless.
Could it oops if cpuid_nent is INT_MAX? If so, it's not entirely harmless.
In this case I'd rather take the occasion to cleanup the code like this
(compile-tested):
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 9fed5bedaad6..2fd6e7169936 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -656,18 +656,19 @@ out:
static int move_to_next_stateful_cpuid_entry(struct kvm_vcpu *vcpu, int i)
{
struct kvm_cpuid_entry2 *e = &vcpu->arch.cpuid_entries[i];
- int j, nent = vcpu->arch.cpuid_nent;
+ struct kvm_cpuid_entry2 *ej;
+ int j = i, nent = vcpu->arch.cpuid_nent;
e->flags &= ~KVM_CPUID_FLAG_STATE_READ_NEXT;
+
/* when no next entry is found, the current entry[i] is reselected */
- for (j = i + 1; ; j = (j + 1) % nent) {
- struct kvm_cpuid_entry2 *ej = &vcpu->arch.cpuid_entries[j];
- if (ej->function == e->function) {
- ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
- return j;
- }
- }
- return 0; /* silence gcc, even though control never reaches here */
+ do {
+ j = (j + 1) % nent;
+ ej = &vcpu->arch.cpuid_entries[j];
+ } while (ej->function != e->function);
+
+ ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
+ return j;
}
/* find an entry with matching function, matching index (if needed), and that
What do you think?
Paolo
^ permalink raw reply related [flat|nested] 10+ messages in thread* Re: [patch RFC] kvm, cpuid: silence a buffer overflow warning
2014-02-20 13:07 ` Paolo Bonzini
@ 2014-02-20 13:18 ` walter harms
-1 siblings, 0 replies; 10+ messages in thread
From: walter harms @ 2014-02-20 13:18 UTC (permalink / raw)
To: Paolo Bonzini
Cc: Dan Carpenter, Gleb Natapov, Thomas Gleixner, Ingo Molnar,
H. Peter Anvin, x86, kvm, kernel-janitors
Am 20.02.2014 14:07, schrieb Paolo Bonzini:
> Il 20/02/2014 13:34, Dan Carpenter ha scritto:
>> This seems like a harmless off by one overflow if "i" is the last
>> element in the vcpu->arch.cpuid_entries[] array.
>>
>> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
>> ---
>> Not tested. I always wonder if it's worth fixing these or if it's worth
>> reporting them? Either of those seem like a lot of work for something
>> harmless.
>
> Could it oops if cpuid_nent is INT_MAX? If so, it's not entirely harmless.
> In this case I'd rather take the occasion to cleanup the code like this
> (compile-tested):
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 9fed5bedaad6..2fd6e7169936 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -656,18 +656,19 @@ out:
> static int move_to_next_stateful_cpuid_entry(struct kvm_vcpu *vcpu, int i)
> {
> struct kvm_cpuid_entry2 *e = &vcpu->arch.cpuid_entries[i];
> - int j, nent = vcpu->arch.cpuid_nent;
> + struct kvm_cpuid_entry2 *ej;
> + int j = i, nent = vcpu->arch.cpuid_nent;
>
> e->flags &= ~KVM_CPUID_FLAG_STATE_READ_NEXT;
> +
> /* when no next entry is found, the current entry[i] is reselected */
> - for (j = i + 1; ; j = (j + 1) % nent) {
> - struct kvm_cpuid_entry2 *ej = &vcpu->arch.cpuid_entries[j];
> - if (ej->function = e->function) {
> - ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
> - return j;
> - }
> - }
> - return 0; /* silence gcc, even though control never reaches here */
> + do {
> + j = (j + 1) % nent;
> + ej = &vcpu->arch.cpuid_entries[j];
> + } while (ej->function != e->function);
> +
> + ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
> + return j;
> }
>
> /* find an entry with matching function, matching index (if needed), and that
>
> What do you think?
>
Is there any guaranty that this will not loop forever ?
an if (i=j) return 0; would be on the save side. (I guess that
these was the idea behind the for).
re,
wh
> Paolo
> --
> To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [patch RFC] kvm, cpuid: silence a buffer overflow warning
@ 2014-02-20 13:18 ` walter harms
0 siblings, 0 replies; 10+ messages in thread
From: walter harms @ 2014-02-20 13:18 UTC (permalink / raw)
To: Paolo Bonzini
Cc: Dan Carpenter, Gleb Natapov, Thomas Gleixner, Ingo Molnar,
H. Peter Anvin, x86, kvm, kernel-janitors
Am 20.02.2014 14:07, schrieb Paolo Bonzini:
> Il 20/02/2014 13:34, Dan Carpenter ha scritto:
>> This seems like a harmless off by one overflow if "i" is the last
>> element in the vcpu->arch.cpuid_entries[] array.
>>
>> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
>> ---
>> Not tested. I always wonder if it's worth fixing these or if it's worth
>> reporting them? Either of those seem like a lot of work for something
>> harmless.
>
> Could it oops if cpuid_nent is INT_MAX? If so, it's not entirely harmless.
> In this case I'd rather take the occasion to cleanup the code like this
> (compile-tested):
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 9fed5bedaad6..2fd6e7169936 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -656,18 +656,19 @@ out:
> static int move_to_next_stateful_cpuid_entry(struct kvm_vcpu *vcpu, int i)
> {
> struct kvm_cpuid_entry2 *e = &vcpu->arch.cpuid_entries[i];
> - int j, nent = vcpu->arch.cpuid_nent;
> + struct kvm_cpuid_entry2 *ej;
> + int j = i, nent = vcpu->arch.cpuid_nent;
>
> e->flags &= ~KVM_CPUID_FLAG_STATE_READ_NEXT;
> +
> /* when no next entry is found, the current entry[i] is reselected */
> - for (j = i + 1; ; j = (j + 1) % nent) {
> - struct kvm_cpuid_entry2 *ej = &vcpu->arch.cpuid_entries[j];
> - if (ej->function == e->function) {
> - ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
> - return j;
> - }
> - }
> - return 0; /* silence gcc, even though control never reaches here */
> + do {
> + j = (j + 1) % nent;
> + ej = &vcpu->arch.cpuid_entries[j];
> + } while (ej->function != e->function);
> +
> + ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
> + return j;
> }
>
> /* find an entry with matching function, matching index (if needed), and that
>
> What do you think?
>
Is there any guaranty that this will not loop forever ?
an if (i==j) return 0; would be on the save side. (I guess that
these was the idea behind the for).
re,
wh
> Paolo
> --
> To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [patch RFC] kvm, cpuid: silence a buffer overflow warning
2014-02-20 13:18 ` walter harms
@ 2014-02-20 13:19 ` Paolo Bonzini
-1 siblings, 0 replies; 10+ messages in thread
From: Paolo Bonzini @ 2014-02-20 13:19 UTC (permalink / raw)
To: wharms
Cc: Dan Carpenter, Gleb Natapov, Thomas Gleixner, Ingo Molnar,
H. Peter Anvin, x86, kvm, kernel-janitors
Il 20/02/2014 14:18, walter harms ha scritto:
>
>
> Am 20.02.2014 14:07, schrieb Paolo Bonzini:
>> Il 20/02/2014 13:34, Dan Carpenter ha scritto:
>>> This seems like a harmless off by one overflow if "i" is the last
>>> element in the vcpu->arch.cpuid_entries[] array.
>>>
>>> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
>>> ---
>>> Not tested. I always wonder if it's worth fixing these or if it's worth
>>> reporting them? Either of those seem like a lot of work for something
>>> harmless.
>>
>> Could it oops if cpuid_nent is INT_MAX? If so, it's not entirely harmless.
>> In this case I'd rather take the occasion to cleanup the code like this
>> (compile-tested):
>>
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index 9fed5bedaad6..2fd6e7169936 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -656,18 +656,19 @@ out:
>> static int move_to_next_stateful_cpuid_entry(struct kvm_vcpu *vcpu, int i)
>> {
>> struct kvm_cpuid_entry2 *e = &vcpu->arch.cpuid_entries[i];
>> - int j, nent = vcpu->arch.cpuid_nent;
>> + struct kvm_cpuid_entry2 *ej;
>> + int j = i, nent = vcpu->arch.cpuid_nent;
>>
>> e->flags &= ~KVM_CPUID_FLAG_STATE_READ_NEXT;
>> +
>> /* when no next entry is found, the current entry[i] is reselected */
>> - for (j = i + 1; ; j = (j + 1) % nent) {
>> - struct kvm_cpuid_entry2 *ej = &vcpu->arch.cpuid_entries[j];
>> - if (ej->function = e->function) {
>> - ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
>> - return j;
>> - }
>> - }
>> - return 0; /* silence gcc, even though control never reaches here */
>> + do {
>> + j = (j + 1) % nent;
>> + ej = &vcpu->arch.cpuid_entries[j];
>> + } while (ej->function != e->function);
>> +
>> + ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
>> + return j;
>> }
>>
>> /* find an entry with matching function, matching index (if needed), and that
>>
>> What do you think?
>>
>
> Is there any guaranty that this will not loop forever ?
>
> an if (i=j) return 0; would be on the save side. (I guess that
> these was the idea behind the for).
Once i=j you'll get ej->function = e->function and exit.
Paolo
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [patch RFC] kvm, cpuid: silence a buffer overflow warning
@ 2014-02-20 13:19 ` Paolo Bonzini
0 siblings, 0 replies; 10+ messages in thread
From: Paolo Bonzini @ 2014-02-20 13:19 UTC (permalink / raw)
To: wharms
Cc: Dan Carpenter, Gleb Natapov, Thomas Gleixner, Ingo Molnar,
H. Peter Anvin, x86, kvm, kernel-janitors
Il 20/02/2014 14:18, walter harms ha scritto:
>
>
> Am 20.02.2014 14:07, schrieb Paolo Bonzini:
>> Il 20/02/2014 13:34, Dan Carpenter ha scritto:
>>> This seems like a harmless off by one overflow if "i" is the last
>>> element in the vcpu->arch.cpuid_entries[] array.
>>>
>>> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
>>> ---
>>> Not tested. I always wonder if it's worth fixing these or if it's worth
>>> reporting them? Either of those seem like a lot of work for something
>>> harmless.
>>
>> Could it oops if cpuid_nent is INT_MAX? If so, it's not entirely harmless.
>> In this case I'd rather take the occasion to cleanup the code like this
>> (compile-tested):
>>
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index 9fed5bedaad6..2fd6e7169936 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -656,18 +656,19 @@ out:
>> static int move_to_next_stateful_cpuid_entry(struct kvm_vcpu *vcpu, int i)
>> {
>> struct kvm_cpuid_entry2 *e = &vcpu->arch.cpuid_entries[i];
>> - int j, nent = vcpu->arch.cpuid_nent;
>> + struct kvm_cpuid_entry2 *ej;
>> + int j = i, nent = vcpu->arch.cpuid_nent;
>>
>> e->flags &= ~KVM_CPUID_FLAG_STATE_READ_NEXT;
>> +
>> /* when no next entry is found, the current entry[i] is reselected */
>> - for (j = i + 1; ; j = (j + 1) % nent) {
>> - struct kvm_cpuid_entry2 *ej = &vcpu->arch.cpuid_entries[j];
>> - if (ej->function == e->function) {
>> - ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
>> - return j;
>> - }
>> - }
>> - return 0; /* silence gcc, even though control never reaches here */
>> + do {
>> + j = (j + 1) % nent;
>> + ej = &vcpu->arch.cpuid_entries[j];
>> + } while (ej->function != e->function);
>> +
>> + ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
>> + return j;
>> }
>>
>> /* find an entry with matching function, matching index (if needed), and that
>>
>> What do you think?
>>
>
> Is there any guaranty that this will not loop forever ?
>
> an if (i==j) return 0; would be on the save side. (I guess that
> these was the idea behind the for).
Once i==j you'll get ej->function == e->function and exit.
Paolo
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [patch RFC] kvm, cpuid: silence a buffer overflow warning
2014-02-20 13:07 ` Paolo Bonzini
@ 2014-02-20 13:23 ` Dan Carpenter
-1 siblings, 0 replies; 10+ messages in thread
From: Dan Carpenter @ 2014-02-20 13:23 UTC (permalink / raw)
To: Paolo Bonzini
Cc: Gleb Natapov, Thomas Gleixner, Ingo Molnar, H. Peter Anvin, x86,
kvm, kernel-janitors
On Thu, Feb 20, 2014 at 02:07:42PM +0100, Paolo Bonzini wrote:
> Il 20/02/2014 13:34, Dan Carpenter ha scritto:
> > This seems like a harmless off by one overflow if "i" is the last
> > element in the vcpu->arch.cpuid_entries[] array.
> >
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > ---
> > Not tested. I always wonder if it's worth fixing these or if it's worth
> > reporting them? Either of those seem like a lot of work for something
> > harmless.
>
> Could it oops if cpuid_nent is INT_MAX?
cpuid_nent is capped at KVM_MAX_CPUID_ENTRIES (80).
regards,
dan carpenter
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [patch RFC] kvm, cpuid: silence a buffer overflow warning
@ 2014-02-20 13:23 ` Dan Carpenter
0 siblings, 0 replies; 10+ messages in thread
From: Dan Carpenter @ 2014-02-20 13:23 UTC (permalink / raw)
To: Paolo Bonzini
Cc: Gleb Natapov, Thomas Gleixner, Ingo Molnar, H. Peter Anvin, x86,
kvm, kernel-janitors
On Thu, Feb 20, 2014 at 02:07:42PM +0100, Paolo Bonzini wrote:
> Il 20/02/2014 13:34, Dan Carpenter ha scritto:
> > This seems like a harmless off by one overflow if "i" is the last
> > element in the vcpu->arch.cpuid_entries[] array.
> >
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > ---
> > Not tested. I always wonder if it's worth fixing these or if it's worth
> > reporting them? Either of those seem like a lot of work for something
> > harmless.
>
> Could it oops if cpuid_nent is INT_MAX?
cpuid_nent is capped at KVM_MAX_CPUID_ENTRIES (80).
regards,
dan carpenter
^ permalink raw reply [flat|nested] 10+ messages in thread