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 <theflow@xxxxxxxxxx>
Reported-by: Peter Gonda <pgonda@xxxxxxxxxx>
Suggested-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
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 <thomas.lendacky@xxxxxxx>
