For some sev ioctl interfaces, input may be passed that is less than or
equal to SEV_FW_BLOB_MAX_SIZE, but larger than the data that PSP
firmware returns. In this case, kmalloc will allocate memory that is the
size of the input rather than the size of the data. Since PSP firmware
doesn't fully overwrite the buffer, the sev ioctl interfaces with the
issue may return uninitialized slab memory.

Currently, all of the ioctl interfaces in the ccp driver are safe, but
to prevent future problems, change all ioctl interfaces that allocate
memory with kmalloc to use kzalloc.

Reported-by: Andy Nguyen <theflow@google.com>
Suggested-by: David Rientjes <rientjes@google.com>
Suggested-by: Peter Gonda <pgonda@google.com>
Signed-off-by: John Allen <john.allen@amd.com>
---
 drivers/crypto/ccp/sev-dev.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 6ab93dfd478a..e2298843ea8a 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -604,7 +604,7 @@ static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp, bool writable)
 	if (input.length > SEV_FW_BLOB_MAX_SIZE)
 		return -EFAULT;
 
-	blob = kmalloc(input.length, GFP_KERNEL);
+	blob = kzalloc(input.length, GFP_KERNEL);
 	if (!blob)
 		return -ENOMEM;
 
@@ -828,7 +828,7 @@ 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 = kmalloc(input.length, GFP_KERNEL);
+		id_blob = kzalloc(input.length, GFP_KERNEL);
 		if (!id_blob)
 			return -ENOMEM;
 
@@ -947,14 +947,14 @@ static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp, bool writable)
 	if (input.cert_chain_len > SEV_FW_BLOB_MAX_SIZE)
 		return -EFAULT;
 
-	pdh_blob = kmalloc(input.pdh_cert_len, GFP_KERNEL);
+	pdh_blob = kzalloc(input.pdh_cert_len, GFP_KERNEL);
 	if (!pdh_blob)
 		return -ENOMEM;
 
 	data.pdh_cert_address = __psp_pa(pdh_blob);
 	data.pdh_cert_len = input.pdh_cert_len;
 
-	cert_blob = kmalloc(input.cert_chain_len, GFP_KERNEL);
+	cert_blob = kzalloc(input.cert_chain_len, GFP_KERNEL);
 	if (!cert_blob) {
 		ret = -ENOMEM;
 		goto e_free_pdh;
-- 
2.34.1

On Thu, May 12, 2022 at 08:34:55PM +0000, John Allen wrote:
> For some sev ioctl interfaces, input may be passed that is less than or
> equal to SEV_FW_BLOB_MAX_SIZE, but larger than the data that PSP
> firmware returns. In this case, kmalloc will allocate memory that is the
> size of the input rather than the size of the data. Since PSP firmware
> doesn't fully overwrite the buffer, the sev ioctl interfaces with the
> issue may return uninitialized slab memory.
> 
> Currently, all of the ioctl interfaces in the ccp driver are safe, but
> to prevent future problems, change all ioctl interfaces that allocate
> memory with kmalloc to use kzalloc.

I should have CC'd stable@vger.kernel.org and added a Fixes tag for
this. I'll send a v2 with these, but I'll give it a couple days for
comments before I do.

Thanks,
John

> 
> Reported-by: Andy Nguyen <theflow@google.com>
> Suggested-by: David Rientjes <rientjes@google.com>
> Suggested-by: Peter Gonda <pgonda@google.com>
> Signed-off-by: John Allen <john.allen@amd.com>
> ---
>  drivers/crypto/ccp/sev-dev.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index 6ab93dfd478a..e2298843ea8a 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -604,7 +604,7 @@ static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp, bool writable)
>  	if (input.length > SEV_FW_BLOB_MAX_SIZE)
>  		return -EFAULT;
>  
> -	blob = kmalloc(input.length, GFP_KERNEL);
> +	blob = kzalloc(input.length, GFP_KERNEL);
>  	if (!blob)
>  		return -ENOMEM;
>  
> @@ -828,7 +828,7 @@ 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 = kmalloc(input.length, GFP_KERNEL);
> +		id_blob = kzalloc(input.length, GFP_KERNEL);
>  		if (!id_blob)
>  			return -ENOMEM;
>  
> @@ -947,14 +947,14 @@ static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp, bool writable)
>  	if (input.cert_chain_len > SEV_FW_BLOB_MAX_SIZE)
>  		return -EFAULT;
>  
> -	pdh_blob = kmalloc(input.pdh_cert_len, GFP_KERNEL);
> +	pdh_blob = kzalloc(input.pdh_cert_len, GFP_KERNEL);
>  	if (!pdh_blob)
>  		return -ENOMEM;
>  
>  	data.pdh_cert_address = __psp_pa(pdh_blob);
>  	data.pdh_cert_len = input.pdh_cert_len;
>  
> -	cert_blob = kmalloc(input.cert_chain_len, GFP_KERNEL);
> +	cert_blob = kzalloc(input.cert_chain_len, GFP_KERNEL);
>  	if (!cert_blob) {
>  		ret = -ENOMEM;
>  		goto e_free_pdh;
> -- 
> 2.34.1
>