[PATCH] KVM: x86: Fix off-by-one error in kvm_vcpu_ioctl_x86_setup_mce

[PATCH] KVM: x86: Fix off-by-one error in kvm_vcpu_ioctl_x86_setup_mce

[Jim Mattson]

Bank_num is a one-based count of banks, not a zero-based index. It
overflows the allocated space only when strictly greater than
KVM_MAX_MCE_BANKS.

Fixes: a9e38c3e01ad ("KVM: x86: Catch potential overrun in MCE setup")
Signed-off-by: Jue Wang <juew@google.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Peter Shier <pshier@google.com>
---
 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d786c7d27ce5..5bf45c9aa8e5 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3751,7 +3751,7 @@ static int kvm_vcpu_ioctl_x86_setup_mce(struct kvm_vcpu *vcpu,
 	unsigned bank_num = mcg_cap & 0xff, bank;
 
 	r = -EINVAL;
-	if (!bank_num || bank_num >= KVM_MAX_MCE_BANKS)
+	if (!bank_num || bank_num > KVM_MAX_MCE_BANKS)
 		goto out;
 	if (mcg_cap & ~(kvm_mce_cap_supported | 0xff | 0xff0000))
 		goto out;
-- 
2.26.2.645.ge9eca65c58-goog

Re: [PATCH] KVM: x86: Fix off-by-one error in kvm_vcpu_ioctl_x86_setup_mce

[Jim Mattson]

On Mon, May 11, 2020 at 3:56 PM Jim Mattson <jmattson@google.com> wrote:
>
> Bank_num is a one-based count of banks, not a zero-based index. It
> overflows the allocated space only when strictly greater than
> KVM_MAX_MCE_BANKS.
>
> Fixes: a9e38c3e01ad ("KVM: x86: Catch potential overrun in MCE setup")
> Signed-off-by: Jue Wang <juew@google.com>
> Signed-off-by: Jim Mattson <jmattson@google.com>
> Reviewed-by: Peter Shier <pshier@google.com>
> ---
>  arch/x86/kvm/x86.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d786c7d27ce5..5bf45c9aa8e5 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3751,7 +3751,7 @@ static int kvm_vcpu_ioctl_x86_setup_mce(struct kvm_vcpu *vcpu,
>         unsigned bank_num = mcg_cap & 0xff, bank;
>
>         r = -EINVAL;
> -       if (!bank_num || bank_num >= KVM_MAX_MCE_BANKS)
> +       if (!bank_num || bank_num > KVM_MAX_MCE_BANKS)
>                 goto out;
>         if (mcg_cap & ~(kvm_mce_cap_supported | 0xff | 0xff0000))
>                 goto out;
> --
> 2.26.2.645.ge9eca65c58-goog
>

Ping?

Re: [PATCH] KVM: x86: Fix off-by-one error in kvm_vcpu_ioctl_x86_setup_mce

[Vitaly Kuznetsov]

Jim Mattson <jmattson@google.com> writes:

> Bank_num is a one-based count of banks, not a zero-based index. It
> overflows the allocated space only when strictly greater than
> KVM_MAX_MCE_BANKS.
>
> Fixes: a9e38c3e01ad ("KVM: x86: Catch potential overrun in MCE setup")
> Signed-off-by: Jue Wang <juew@google.com>
> Signed-off-by: Jim Mattson <jmattson@google.com>
> Reviewed-by: Peter Shier <pshier@google.com>
> ---
>  arch/x86/kvm/x86.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d786c7d27ce5..5bf45c9aa8e5 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3751,7 +3751,7 @@ static int kvm_vcpu_ioctl_x86_setup_mce(struct kvm_vcpu *vcpu,
>  	unsigned bank_num = mcg_cap & 0xff, bank;

/* it would be great to get rid of bare unsigned-s in
kvm_vcpu_ioctl_x86_setup_mce/kvm_vcpu_ioctl_x86_set_mce ... */

>  
>  	r = -EINVAL;
> -	if (!bank_num || bank_num >= KVM_MAX_MCE_BANKS)
> +	if (!bank_num || bank_num > KVM_MAX_MCE_BANKS)
>  		goto out;
>  	if (mcg_cap & ~(kvm_mce_cap_supported | 0xff | 0xff0000))
>  		goto out;

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

-- 
Vitaly

Re: [PATCH] KVM: x86: Fix off-by-one error in kvm_vcpu_ioctl_x86_setup_mce

[Paolo Bonzini]

On 12/05/20 00:56, Jim Mattson wrote:
> Bank_num is a one-based count of banks, not a zero-based index. It
> overflows the allocated space only when strictly greater than
> KVM_MAX_MCE_BANKS.
> 
> Fixes: a9e38c3e01ad ("KVM: x86: Catch potential overrun in MCE setup")
> Signed-off-by: Jue Wang <juew@google.com>
> Signed-off-by: Jim Mattson <jmattson@google.com>
> Reviewed-by: Peter Shier <pshier@google.com>
> ---
>  arch/x86/kvm/x86.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d786c7d27ce5..5bf45c9aa8e5 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3751,7 +3751,7 @@ static int kvm_vcpu_ioctl_x86_setup_mce(struct kvm_vcpu *vcpu,
>  	unsigned bank_num = mcg_cap & 0xff, bank;
>  
>  	r = -EINVAL;
> -	if (!bank_num || bank_num >= KVM_MAX_MCE_BANKS)
> +	if (!bank_num || bank_num > KVM_MAX_MCE_BANKS)
>  		goto out;
>  	if (mcg_cap & ~(kvm_mce_cap_supported | 0xff | 0xff0000))
>  		goto out;
> 

Queued, thanks.

Paolo