Re: [PATCH] KVM: x86: Assertions to check no overrun in MSR lists

[Paolo Bonzini]

Il 24/07/2014 14:06, Nadav Amit ha scritto:
> Currently there is no check whether shared MSRs list overrun the allocated size
> which can results in bugs. In addition there is no check that vmx->guest_msrs
> has sufficient space to accommodate all the VMX msrs.  This patch adds the
> assertions.
> 
> Signed-off-by: Nadav Amit <namit@xxxxxxxxxxxxxxxxx>
> ---
>  arch/x86/kvm/vmx.c | 2 ++
>  arch/x86/kvm/x86.c | 1 +
>  2 files changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 7534a9f..286a931 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -7585,6 +7585,8 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>  		goto free_vcpu;
>  
>  	vmx->guest_msrs = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +	BUILD_BUG_ON(PAGE_SIZE / sizeof(struct shared_msr_entry) < NR_VMX_MSR);
> +
>  	err = -ENOMEM;
>  	if (!vmx->guest_msrs) {
>  		goto uninit_vcpu;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f750b69..f5cd7876 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -212,6 +212,7 @@ static void shared_msr_update(unsigned slot, u32 msr)
>  
>  void kvm_define_shared_msr(unsigned slot, u32 msr)
>  {
> +	BUG_ON(slot >= KVM_NR_SHARED_MSRS);
>  	if (slot >= shared_msrs_global.nr)
>  		shared_msrs_global.nr = slot + 1;
>  	shared_msrs_global.msrs[slot] = msr;
> 

Thanks, both are good improvements.  I'm adding this patch on top.

-------------------- 8< ---------------------
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Subject: [PATCH] Replace NR_VMX_MSR with its definition

Using ARRAY_SIZE directly makes it easier to read the code.  While touching
the code, replace the division by a multiplication in the recently added
BUILD_BUG_ON.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 3397a88b7463..906f9e49d0e7 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -823,7 +823,6 @@ static const u32 vmx_msr_index[] = {
 #endif
 	MSR_EFER, MSR_TSC_AUX, MSR_STAR,
 };
-#define NR_VMX_MSR ARRAY_SIZE(vmx_msr_index)
 
 static inline bool is_page_fault(u32 intr_info)
 {
@@ -4441,7 +4440,7 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
 		vmx->vcpu.arch.pat = host_pat;
 	}
 
-	for (i = 0; i < NR_VMX_MSR; ++i) {
+	for (i = 0; i < ARRAY_SIZE(vmx_msr_index); ++i) {
 		u32 index = vmx_msr_index[i];
 		u32 data_low, data_high;
 		int j = vmx->nmsrs;
@@ -7608,7 +7607,8 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
 		goto free_vcpu;
 
 	vmx->guest_msrs = kmalloc(PAGE_SIZE, GFP_KERNEL);
-	BUILD_BUG_ON(PAGE_SIZE / sizeof(struct shared_msr_entry) < NR_VMX_MSR);
+	BUILD_BUG_ON(ARRAY_SIZE(vmx_msr_index) * sizeof(vmx->guest_msrs[0])
+		     > PAGE_SIZE);
 
 	err = -ENOMEM;
 	if (!vmx->guest_msrs) {
@@ -8960,7 +8960,7 @@ static int __init vmx_init(void)
 
 	rdmsrl_safe(MSR_EFER, &host_efer);
 
-	for (i = 0; i < NR_VMX_MSR; ++i)
+	for (i = 0; i < ARRAY_SIZE(vmx_msr_index); ++i)
 		kvm_define_shared_msr(i, vmx_msr_index[i]);
 
 	vmx_io_bitmap_a = (unsigned long *)__get_free_page(GFP_KERNEL);

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