linux-kernel - [PATCH] KVM: Use previously computed array

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Date:   Sat, 30 May 2020 17:35:58 +0300
From:   Denis Efremov <efremov@...ux.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Denis Efremov <efremov@...ux.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: Use previously computed array_size()

array_size() is used in alloc calls to compute the allocation
size. Next, "raw" multiplication is used to compute the size
for copy_from_user(). The patch removes duplicated computation
by saving the size in a var. No security concerns, just a small
optimization.

Signed-off-by: Denis Efremov <efremov@...ux.com>
---
 arch/x86/kvm/cpuid.c | 9 ++++-----
 virt/kvm/kvm_main.c  | 8 ++++----
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 901cd1fdecd9..3363b7531af1 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -184,14 +184,13 @@ int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
 		goto out;
 	r = -ENOMEM;
 	if (cpuid->nent) {
-		cpuid_entries =
-			vmalloc(array_size(sizeof(struct kvm_cpuid_entry),
-					   cpuid->nent));
+		const size_t size = array_size(sizeof(struct kvm_cpuid_entry),
+					       cpuid->nent);
+		cpuid_entries = vmalloc(size);
 		if (!cpuid_entries)
 			goto out;
 		r = -EFAULT;
-		if (copy_from_user(cpuid_entries, entries,
-				   cpuid->nent * sizeof(struct kvm_cpuid_entry)))
+		if (copy_from_user(cpuid_entries, entries, size))
 			goto out;
 	}
 	for (i = 0; i < cpuid->nent; i++) {
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 731c1e517716..001e1929e01c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3722,15 +3722,15 @@ static long kvm_vm_ioctl(struct file *filp,
 		if (routing.flags)
 			goto out;
 		if (routing.nr) {
+			const size_t size = array_size(sizeof(*entries),
+						       routing.nr);
 			r = -ENOMEM;
-			entries = vmalloc(array_size(sizeof(*entries),
-						     routing.nr));
+			entries = vmalloc(size);
 			if (!entries)
 				goto out;
 			r = -EFAULT;
 			urouting = argp;
-			if (copy_from_user(entries, urouting->entries,
-					   routing.nr * sizeof(*entries)))
+			if (copy_from_user(entries, urouting->entries, size))
 				goto out_free_irq_routing;
 		}
 		r = kvm_set_irq_routing(kvm, entries, routing.nr,
-- 
2.26.2