Currently userspace can ask for any uint32 size allocation for the
SEV_GET_ID2. Limit this allocation size to the max physically
contiguously allocation: MAX_ORDER.
Reported-by: Andy Nguyen <[email protected]>
Suggested-by: David Rientjes <[email protected]>
Signed-off-by: Peter Gonda <[email protected]>
Cc: [email protected]
Cc: Herbert Xu <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: John Allen <[email protected]>
Cc: Thomas.Lendacky <[email protected]>
---
drivers/crypto/ccp/sev-dev.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 06fc7156c04f..5c16c4406764 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -878,6 +878,10 @@ static int sev_ioctl_do_get_id2(struct sev_issue_cmd *argp)
if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
return -EFAULT;
+ /* Max length that can be allocated physically contiguously */
+ if (get_order(input.length) >= MAX_ORDER)
+ return -ENOMEM;
+
input_address = (void __user *)input.address;
if (input.address && input.length) {
--
2.39.0.rc1.256.g54fd8350bd-goog
On Thu, 15 Dec 2022, Herbert Xu wrote:
> On Wed, Dec 14, 2022 at 12:20:46PM -0800, Peter Gonda wrote:
> > Currently userspace can ask for any uint32 size allocation for the
> > SEV_GET_ID2. Limit this allocation size to the max physically
> > contiguously allocation: MAX_ORDER.
>
> This is just to silence the alloc_pages warning, right? If so
> how about adding __GFP_NOWARN instead?
>
The goal was to be more explicit about that, but setting __GFP_NOWARN
would result in the same functional behavior. If we're to go that route,
it would likely be best to add a comment about the limitation.
That said, if AMD would prefer this to be an EINVAL instead of a ENOMEM by
introducing a more formal limitation on the length that can be used, that
would be preferred so that we don't need to rely on the page allocator's
max length to enforce this arbitrarily.
On Tue, Dec 27, 2022 at 05:42:31PM -0800, David Rientjes wrote:
>
> The goal was to be more explicit about that, but setting __GFP_NOWARN
> would result in the same functional behavior. If we're to go that route,
> it would likely be best to add a comment about the limitation.
>
> That said, if AMD would prefer this to be an EINVAL instead of a ENOMEM by
> introducing a more formal limitation on the length that can be used, that
> would be preferred so that we don't need to rely on the page allocator's
> max length to enforce this arbitrarily.
Ideally the limit should be set according to the object that
you're trying to allocate. But if that is truly unlimited,
and you don't want to see a warning, then GFP_NOWARN seems to
fit the bill.
Thanks,
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
On Wed, 28 Dec 2022, Herbert Xu wrote:
> On Tue, Dec 27, 2022 at 05:42:31PM -0800, David Rientjes wrote:
> >
> > The goal was to be more explicit about that, but setting __GFP_NOWARN
> > would result in the same functional behavior. If we're to go that route,
> > it would likely be best to add a comment about the limitation.
> >
> > That said, if AMD would prefer this to be an EINVAL instead of a ENOMEM by
> > introducing a more formal limitation on the length that can be used, that
> > would be preferred so that we don't need to rely on the page allocator's
> > max length to enforce this arbitrarily.
>
> Ideally the limit should be set according to the object that
> you're trying to allocate. But if that is truly unlimited,
> and you don't want to see a warning, then GFP_NOWARN seems to
> fit the bill.
>
AMD would be able to speak authoritatively on it, but I think the length
of the ID isn't to be assumed by software because it will likely change
later.
I don't think there's an active vulnerability with the currnet code so we
can likely drop [email protected] for this. The kzalloc() will fail
if you try to allocate over 2MB. If you try to allocate >32KB, the page
allocator will attempt to reclaim but won't oom kill. If you try to
allocate <=32KB, there's the potential for oom kill if nothing is
reclaimable, but if memory is that scarce I think we have bigger problems.
So __GFP_NOWARN will work, but I also think it's subtle enough that it
warrants being coupled with a comment.
For SEV_GET_ID2, the user provided length does not have a specified
limitation because the length of the ID may change in the future. The
kernel memory allocation, however, is implicitly limited to 4MB on x86 by
the page allocator, otherwise the kzalloc() will fail.
When this happens, it is best not to spam the kernel log with the warning.
Simply fail the allocation and return ENOMEM to the user.
Fixes: d6112ea0cb34 ("crypto: ccp - introduce SEV_GET_ID2 command")
Reported-by: Andy Nguyen <[email protected]>
Reported-by: Peter Gonda <[email protected]>
Suggested-by: Herbert Xu <[email protected]>
Signed-off-by: David Rientjes <[email protected]>
---
drivers/crypto/ccp/sev-dev.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -881,7 +881,14 @@ static int sev_ioctl_do_get_id2(struct sev_issue_cmd *argp)
input_address = (void __user *)input.address;
if (input.address && input.length) {
- id_blob = kzalloc(input.length, GFP_KERNEL);
+ /*
+ * The length of the ID shouldn't be assumed by software since
+ * it may change in the future. The allocation size is limited
+ * to 1 << (PAGE_SHIFT + MAX_ORDER - 1) by the page allocator.
+ * If the allocation fails, simply return ENOMEM rather than
+ * warning in the kernel log.
+ */
+ id_blob = kzalloc(input.length, GFP_KERNEL | __GFP_NOWARN);
if (!id_blob)
return -ENOMEM;
On 12/30/22 16:18, David Rientjes wrote:
> For SEV_GET_ID2, the user provided length does not have a specified
> limitation because the length of the ID may change in the future. The
> kernel memory allocation, however, is implicitly limited to 4MB on x86 by
> the page allocator, otherwise the kzalloc() will fail.
>
> When this happens, it is best not to spam the kernel log with the warning.
> Simply fail the allocation and return ENOMEM to the user.
>
> Fixes: d6112ea0cb34 ("crypto: ccp - introduce SEV_GET_ID2 command")
> Reported-by: Andy Nguyen <[email protected]>
> Reported-by: Peter Gonda <[email protected]>
> Suggested-by: Herbert Xu <[email protected]>
> Signed-off-by: David Rientjes <[email protected]>
> ---
> drivers/crypto/ccp/sev-dev.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -881,7 +881,14 @@ static int sev_ioctl_do_get_id2(struct sev_issue_cmd *argp)
> input_address = (void __user *)input.address;
>
> if (input.address && input.length) {
> - id_blob = kzalloc(input.length, GFP_KERNEL);
> + /*
> + * The length of the ID shouldn't be assumed by software since
> + * it may change in the future. The allocation size is limited
> + * to 1 << (PAGE_SHIFT + MAX_ORDER - 1) by the page allocator.
> + * If the allocation fails, simply return ENOMEM rather than
> + * warning in the kernel log.
> + */
> + id_blob = kzalloc(input.length, GFP_KERNEL | __GFP_NOWARN);
We could do this or we could have the driver invoke the API with a zero
length to get the minimum buffer size needed for the call. The driver
could then perform some validation checks comparing the supplied
input.length to the returned length. If the driver can proceed, then if
input.length is exactly 2x the minimum length, then kzalloc the 2 *
minimum length, otherwise kzalloc the minimum length. This is a bit more
complicated, though, compared to this fix.
Either way, is fine with me. Thoughts?
Thanks,
Tom
> if (!id_blob)
> return -ENOMEM;
>
On Tue, 3 Jan 2023, Tom Lendacky wrote:
> On 12/30/22 16:18, David Rientjes wrote:
> > For SEV_GET_ID2, the user provided length does not have a specified
> > limitation because the length of the ID may change in the future. The
> > kernel memory allocation, however, is implicitly limited to 4MB on x86 by
> > the page allocator, otherwise the kzalloc() will fail.
> >
> > When this happens, it is best not to spam the kernel log with the warning.
> > Simply fail the allocation and return ENOMEM to the user.
> >
> > Fixes: d6112ea0cb34 ("crypto: ccp - introduce SEV_GET_ID2 command")
> > Reported-by: Andy Nguyen <[email protected]>
> > Reported-by: Peter Gonda <[email protected]>
> > Suggested-by: Herbert Xu <[email protected]>
> > Signed-off-by: David Rientjes <[email protected]>
> > ---
> > drivers/crypto/ccp/sev-dev.c | 9 ++++++++-
> > 1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> > --- a/drivers/crypto/ccp/sev-dev.c
> > +++ b/drivers/crypto/ccp/sev-dev.c
> > @@ -881,7 +881,14 @@ static int sev_ioctl_do_get_id2(struct sev_issue_cmd
> > *argp)
> > input_address = (void __user *)input.address;
> > if (input.address && input.length) {
> > - id_blob = kzalloc(input.length, GFP_KERNEL);
> > + /*
> > + * The length of the ID shouldn't be assumed by software since
> > + * it may change in the future. The allocation size is
> > limited
> > + * to 1 << (PAGE_SHIFT + MAX_ORDER - 1) by the page allocator.
> > + * If the allocation fails, simply return ENOMEM rather than
> > + * warning in the kernel log.
> > + */
> > + id_blob = kzalloc(input.length, GFP_KERNEL | __GFP_NOWARN);
>
> We could do this or we could have the driver invoke the API with a zero length
> to get the minimum buffer size needed for the call. The driver could then
> perform some validation checks comparing the supplied input.length to the
> returned length. If the driver can proceed, then if input.length is exactly 2x
> the minimum length, then kzalloc the 2 * minimum length, otherwise kzalloc the
> minimum length. This is a bit more complicated, though, compared to this fix.
>
Thanks Tom. IIUC, this could be useful to identify situations where
input.length != min_length and input.length != min_length*2 and, in those
cases, return EINVAL? Or are there situations where this is actually a
valid input.length?
I was assuming that the user was always doing its own SEV_GET_ID2 first to
determine the length and then use it for input.length, but perhaps that's
not the case and they are passing a bogus value.
On 1/3/23 17:18, David Rientjes wrote:
> On Tue, 3 Jan 2023, Tom Lendacky wrote:
>
>> On 12/30/22 16:18, David Rientjes wrote:
>>> For SEV_GET_ID2, the user provided length does not have a specified
>>> limitation because the length of the ID may change in the future. The
>>> kernel memory allocation, however, is implicitly limited to 4MB on x86 by
>>> the page allocator, otherwise the kzalloc() will fail.
>>>
>>> When this happens, it is best not to spam the kernel log with the warning.
>>> Simply fail the allocation and return ENOMEM to the user.
>>>
>>> Fixes: d6112ea0cb34 ("crypto: ccp - introduce SEV_GET_ID2 command")
>>> Reported-by: Andy Nguyen <[email protected]>
>>> Reported-by: Peter Gonda <[email protected]>
>>> Suggested-by: Herbert Xu <[email protected]>
>>> Signed-off-by: David Rientjes <[email protected]>
>>> ---
>>> drivers/crypto/ccp/sev-dev.c | 9 ++++++++-
>>> 1 file changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
>>> --- a/drivers/crypto/ccp/sev-dev.c
>>> +++ b/drivers/crypto/ccp/sev-dev.c
>>> @@ -881,7 +881,14 @@ static int sev_ioctl_do_get_id2(struct sev_issue_cmd
>>> *argp)
>>> input_address = (void __user *)input.address;
>>> if (input.address && input.length) {
>>> - id_blob = kzalloc(input.length, GFP_KERNEL);
>>> + /*
>>> + * The length of the ID shouldn't be assumed by software since
>>> + * it may change in the future. The allocation size is
>>> limited
>>> + * to 1 << (PAGE_SHIFT + MAX_ORDER - 1) by the page allocator.
>>> + * If the allocation fails, simply return ENOMEM rather than
>>> + * warning in the kernel log.
>>> + */
>>> + id_blob = kzalloc(input.length, GFP_KERNEL | __GFP_NOWARN);
>>
>> We could do this or we could have the driver invoke the API with a zero length
>> to get the minimum buffer size needed for the call. The driver could then
>> perform some validation checks comparing the supplied input.length to the
>> returned length. If the driver can proceed, then if input.length is exactly 2x
>> the minimum length, then kzalloc the 2 * minimum length, otherwise kzalloc the
>> minimum length. This is a bit more complicated, though, compared to this fix.
>>
>
> Thanks Tom. IIUC, this could be useful to identify situations where
> input.length != min_length and input.length != min_length*2 and, in those
> cases, return EINVAL? Or are there situations where this is actually a
> valid input.length?
>
> I was assuming that the user was always doing its own SEV_GET_ID2 first to
> determine the length and then use it for input.length, but perhaps that's
> not the case and they are passing a bogus value.
Except that if the user was always doing that, then we wouldn't be worried
about this case then. But, I think my method is overkill and the simple
approach of this patch is the way to go.
Thanks,
Tom
On Wed, 4 Jan 2023, Tom Lendacky wrote:
> > > > For SEV_GET_ID2, the user provided length does not have a specified
> > > > limitation because the length of the ID may change in the future. The
> > > > kernel memory allocation, however, is implicitly limited to 4MB on x86
> > > > by
> > > > the page allocator, otherwise the kzalloc() will fail.
> > > >
> > > > When this happens, it is best not to spam the kernel log with the
> > > > warning.
> > > > Simply fail the allocation and return ENOMEM to the user.
> > > >
> > > > Fixes: d6112ea0cb34 ("crypto: ccp - introduce SEV_GET_ID2 command")
> > > > Reported-by: Andy Nguyen <[email protected]>
> > > > Reported-by: Peter Gonda <[email protected]>
> > > > Suggested-by: Herbert Xu <[email protected]>
> > > > Signed-off-by: David Rientjes <[email protected]>
> > > > ---
> > > > drivers/crypto/ccp/sev-dev.c | 9 ++++++++-
> > > > 1 file changed, 8 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> > > > --- a/drivers/crypto/ccp/sev-dev.c
> > > > +++ b/drivers/crypto/ccp/sev-dev.c
> > > > @@ -881,7 +881,14 @@ static int sev_ioctl_do_get_id2(struct
> > > > sev_issue_cmd
> > > > *argp)
> > > > input_address = (void __user *)input.address;
> > > > if (input.address && input.length) {
> > > > - id_blob = kzalloc(input.length, GFP_KERNEL);
> > > > + /*
> > > > + * The length of the ID shouldn't be assumed by software since
> > > > + * it may change in the future. The allocation size is
> > > > limited
> > > > + * to 1 << (PAGE_SHIFT + MAX_ORDER - 1) by the page allocator.
> > > > + * If the allocation fails, simply return ENOMEM rather than
> > > > + * warning in the kernel log.
> > > > + */
> > > > + id_blob = kzalloc(input.length, GFP_KERNEL | __GFP_NOWARN);
> > >
> > > We could do this or we could have the driver invoke the API with a zero
> > > length
> > > to get the minimum buffer size needed for the call. The driver could then
> > > perform some validation checks comparing the supplied input.length to the
> > > returned length. If the driver can proceed, then if input.length is
> > > exactly 2x
> > > the minimum length, then kzalloc the 2 * minimum length, otherwise kzalloc
> > > the
> > > minimum length. This is a bit more complicated, though, compared to this
> > > fix.
> > >
> >
> > Thanks Tom. IIUC, this could be useful to identify situations where
> > input.length != min_length and input.length != min_length*2 and, in those
> > cases, return EINVAL? Or are there situations where this is actually a
> > valid input.length?
> >
> > I was assuming that the user was always doing its own SEV_GET_ID2 first to
> > determine the length and then use it for input.length, but perhaps that's
> > not the case and they are passing a bogus value.
>
> Except that if the user was always doing that, then we wouldn't be worried
> about this case then. But, I think my method is overkill and the simple
> approach of this patch is the way to go.
>
Makes sense, thanks for the clarification. Does that translate into an
acked-by? :)
On 1/4/23 19:49, David Rientjes wrote:
> On Wed, 4 Jan 2023, Tom Lendacky wrote:
>
>>>>> For SEV_GET_ID2, the user provided length does not have a specified
>>>>> limitation because the length of the ID may change in the future. The
>>>>> kernel memory allocation, however, is implicitly limited to 4MB on x86
>>>>> by
>>>>> the page allocator, otherwise the kzalloc() will fail.
>>>>>
>>>>> When this happens, it is best not to spam the kernel log with the
>>>>> warning.
>>>>> Simply fail the allocation and return ENOMEM to the user.
>>>>>
>>>>> Fixes: d6112ea0cb34 ("crypto: ccp - introduce SEV_GET_ID2 command")
>>>>> Reported-by: Andy Nguyen <[email protected]>
>>>>> Reported-by: Peter Gonda <[email protected]>
>>>>> Suggested-by: Herbert Xu <[email protected]>
>>>>> Signed-off-by: David Rientjes <[email protected]>
>>>>> ---
>>>>> drivers/crypto/ccp/sev-dev.c | 9 ++++++++-
>>>>> 1 file changed, 8 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
>>>>> --- a/drivers/crypto/ccp/sev-dev.c
>>>>> +++ b/drivers/crypto/ccp/sev-dev.c
>>>>> @@ -881,7 +881,14 @@ static int sev_ioctl_do_get_id2(struct
>>>>> sev_issue_cmd
>>>>> *argp)
>>>>> input_address = (void __user *)input.address;
>>>>> if (input.address && input.length) {
>>>>> - id_blob = kzalloc(input.length, GFP_KERNEL);
>>>>> + /*
>>>>> + * The length of the ID shouldn't be assumed by software since
>>>>> + * it may change in the future. The allocation size is
>>>>> limited
>>>>> + * to 1 << (PAGE_SHIFT + MAX_ORDER - 1) by the page allocator.
>>>>> + * If the allocation fails, simply return ENOMEM rather than
>>>>> + * warning in the kernel log.
>>>>> + */
>>>>> + id_blob = kzalloc(input.length, GFP_KERNEL | __GFP_NOWARN);
>>>>
>>>> We could do this or we could have the driver invoke the API with a zero
>>>> length
>>>> to get the minimum buffer size needed for the call. The driver could then
>>>> perform some validation checks comparing the supplied input.length to the
>>>> returned length. If the driver can proceed, then if input.length is
>>>> exactly 2x
>>>> the minimum length, then kzalloc the 2 * minimum length, otherwise kzalloc
>>>> the
>>>> minimum length. This is a bit more complicated, though, compared to this
>>>> fix.
>>>>
>>>
>>> Thanks Tom. IIUC, this could be useful to identify situations where
>>> input.length != min_length and input.length != min_length*2 and, in those
>>> cases, return EINVAL? Or are there situations where this is actually a
>>> valid input.length?
>>>
>>> I was assuming that the user was always doing its own SEV_GET_ID2 first to
>>> determine the length and then use it for input.length, but perhaps that's
>>> not the case and they are passing a bogus value.
>>
>> Except that if the user was always doing that, then we wouldn't be worried
>> about this case then. But, I think my method is overkill and the simple
>> approach of this patch is the way to go.
>>
>
> Makes sense, thanks for the clarification. Does that translate into an
> acked-by? :)
Ah, yeah, forgot about that!
Acked-by: Tom Lendacky <[email protected]>
On Fri, Dec 30, 2022 at 02:18:46PM -0800, David Rientjes wrote:
> For SEV_GET_ID2, the user provided length does not have a specified
> limitation because the length of the ID may change in the future. The
> kernel memory allocation, however, is implicitly limited to 4MB on x86 by
> the page allocator, otherwise the kzalloc() will fail.
>
> When this happens, it is best not to spam the kernel log with the warning.
> Simply fail the allocation and return ENOMEM to the user.
>
> Fixes: d6112ea0cb34 ("crypto: ccp - introduce SEV_GET_ID2 command")
> Reported-by: Andy Nguyen <[email protected]>
> Reported-by: Peter Gonda <[email protected]>
> Suggested-by: Herbert Xu <[email protected]>
> Signed-off-by: David Rientjes <[email protected]>
> ---
> drivers/crypto/ccp/sev-dev.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
Patch applied. Thanks.
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt