Messages in this thread | | | Subject | Re: [PATCH] KVM: X86: prevent integer overflows in KVM_MEMORY_ENCRYPT_REG_REGION | From | Brijesh Singh <> | Date | Mon, 21 May 2018 10:52:33 -0500 |
| |
Hi Dan,
On 05/19/2018 01:01 AM, Dan Carpenter wrote: > 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. >
Please note that SEV is not available on 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 think this should be fine.
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. >
This change looks good. thanks
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>
> --- > Again, this is a static checker fix. The most risky parts of this > patch are blocking "ulen == 0" and changing the types of "first" and > "last". I felt like those changes made the math easier to understand > > 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; >
| |