linux-kernel - Re: [PATCH v1 01/13] KVM: Add KVM_MEM

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Message-ID: <20241206224658.2833655-1-jthoughton@google.com>
Date: Fri,  6 Dec 2024 22:46:58 +0000
From: James Houghton <jthoughton@...gle.com>
To: lkp@...el.com
Cc: amoorthy@...gle.com, corbet@....net, dmatlack@...gle.com, 
	jthoughton@...gle.com, kalyazin@...zon.com, kvm@...r.kernel.org, 
	kvmarm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, maz@...nel.org, 
	oe-kbuild-all@...ts.linux.dev, oliver.upton@...ux.dev, pbonzini@...hat.com, 
	peterx@...hat.com, pgonda@...gle.com, seanjc@...gle.com, wei.w.wang@...el.com, 
	yan.y.zhao@...el.com
Subject: Re: [PATCH v1 01/13] KVM: Add KVM_MEM_USERFAULT memslot flag and bitmap

>    arch/x86/kvm/../../../virt/kvm/kvm_main.c: In function '__kvm_set_memory_region':
> >> arch/x86/kvm/../../../virt/kvm/kvm_main.c:2049:41: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
>     2049 |                 new->userfault_bitmap = (unsigned long *)mem->userfault_bitmap;
>          |                                         ^

I realize that, not only have I done this cast slightly wrong, I'm
missing a few checks on userfault_bitmap that I should have. Applying
this diff, or at least something like it, to fix it:

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b552cdef2850..30f09141df64 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1977,6 +1977,12 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		return -EINVAL;
 	if ((mem->memory_size >> PAGE_SHIFT) > KVM_MEM_MAX_NR_PAGES)
 		return -EINVAL;
+	if (mem->flags & KVM_MEM_USERFAULT &&
+	    ((mem->userfault_bitmap != untagged_addr(mem->userfault_bitmap)) ||
+	     !access_ok((void __user *)(unsigned long)mem->userfault_bitmap,
+			DIV_ROUND_UP(mem->memory_size >> PAGE_SHIFT, BITS_PER_LONG)
+			 * sizeof(long))))
+		return -EINVAL;
 
 	slots = __kvm_memslots(kvm, as_id);
 
@@ -2053,7 +2059,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			goto out;
 	}
 	if (mem->flags & KVM_MEM_USERFAULT)
-		new->userfault_bitmap = (unsigned long *)mem->userfault_bitmap;
+		new->userfault_bitmap =
+		  (unsigned long __user *)(unsigned long)mem->userfault_bitmap;
 
 	r = kvm_set_memslot(kvm, old, new, change);
 	if (r)