From 86bf20cb57b9570262338752c9df580328bc5632 Mon Sep 17 00:00:00 2001 From: Dan Carpenter Date: Sat, 19 May 2018 09:01:36 +0300 Subject: [PATCH] KVM: x86: prevent integer overflows in KVM_MEMORY_ENCRYPT_REG_REGION MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit This is a fix from reviewing the code, but it looks like it might be able to lead to an Oops. It affects 32bit systems. The KVM_MEMORY_ENCRYPT_REG_REGION ioctl uses a u64 for range->addr and range->size but the high 32 bits would be truncated away on a 32 bit system. This is harmless but it's also harmless to prevent it. Then in sev_pin_memory() the "uaddr + ulen" calculation can wrap around. The wrap around can happen on 32 bit or 64 bit systems, but I was only able to figure out a problem for 32 bit systems. We would pick a number which results in "npages" being zero. The sev_pin_memory() would then return ZERO_SIZE_PTR without allocating anything. I made it illegal to call sev_pin_memory() with "ulen" set to zero. Hopefully, that doesn't cause any problems. I also changed the type of "first" and "last" to long, just for cosmetic reasons. Otherwise on a 64 bit system you're saving "uaddr >> 12" in an int and it truncates the high 20 bits away. The math works in the current code so far as I can see but it's just weird. Signed-off-by: Dan Carpenter [Brijesh noted that the code is only reachable on X86_64.] Reviewed-by: Brijesh Singh Signed-off-by: Radim Krčmář --- arch/x86/kvm/svm.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index 220e5a89465a..de21d5c5168b 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -1762,7 +1762,10 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr, unsigned long npages, npinned, size; unsigned long locked, lock_limit; struct page **pages; - int first, last; + unsigned long first, last; + + if (ulen == 0 || uaddr + ulen < uaddr) + return NULL; /* Calculate number of pages. */ first = (uaddr & PAGE_MASK) >> PAGE_SHIFT; @@ -6925,6 +6928,9 @@ static int svm_register_enc_region(struct kvm *kvm, if (!sev_guest(kvm)) return -ENOTTY; + if (range->addr > ULONG_MAX || range->size > ULONG_MAX) + return -EINVAL; + region = kzalloc(sizeof(*region), GFP_KERNEL); if (!region) return -ENOMEM; -- 2.34.1