* [PATCH] KVM: X86: prevent integer overflows in KVM_MEMORY_ENCRYPT_REG_REGION
@ 2018-05-19 6:01 Dan Carpenter
2018-05-21 15:52 ` Brijesh Singh
0 siblings, 1 reply; 3+ messages in thread
From: Dan Carpenter @ 2018-05-19 6:01 UTC (permalink / raw)
To: Joerg Roedel
Cc: Paolo Bonzini, Radim Krčmář,
Thomas Gleixner, Ingo Molnar, H. Peter Anvin, x86, kvm,
linux-kernel, kernel-janitors
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 <dan.carpenter@oracle.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;
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: X86: prevent integer overflows in KVM_MEMORY_ENCRYPT_REG_REGION
2018-05-19 6:01 [PATCH] KVM: X86: prevent integer overflows in KVM_MEMORY_ENCRYPT_REG_REGION Dan Carpenter
@ 2018-05-21 15:52 ` Brijesh Singh
2018-05-26 14:24 ` Radim Krčmář
0 siblings, 1 reply; 3+ messages in thread
From: Brijesh Singh @ 2018-05-21 15:52 UTC (permalink / raw)
To: Dan Carpenter, Joerg Roedel
Cc: brijesh.singh, Paolo Bonzini, Radim Krčmář,
Thomas Gleixner, Ingo Molnar, H. Peter Anvin, x86, kvm,
linux-kernel, kernel-janitors
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;
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] KVM: X86: prevent integer overflows in KVM_MEMORY_ENCRYPT_REG_REGION
2018-05-21 15:52 ` Brijesh Singh
@ 2018-05-26 14:24 ` Radim Krčmář
0 siblings, 0 replies; 3+ messages in thread
From: Radim Krčmář @ 2018-05-26 14:24 UTC (permalink / raw)
To: Brijesh Singh
Cc: Dan Carpenter, Joerg Roedel, Paolo Bonzini, Thomas Gleixner,
Ingo Molnar, H. Peter Anvin, x86, kvm, linux-kernel,
kernel-janitors
2018-05-21 10:52-0500, Brijesh Singh:
> 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.
Added this note and queued, thanks.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2018-05-19 6:01 [PATCH] KVM: X86: prevent integer overflows in KVM_MEMORY_ENCRYPT_REG_REGION Dan Carpenter
2018-05-21 15:52 ` Brijesh Singh
2018-05-26 14:24 ` Radim Krčmář
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