linux-kernel - Re: [PATCH v3] crypto: ccp - Use kzalloc for sev ioctl interfaces to prevent kernel memory leak

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Date:   Tue, 17 May 2022 11:06:07 -0500
From:   John Allen <john.allen@....com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     herbert@...dor.apana.org.au, linux-crypto@...r.kernel.org,
        seanjc@...gle.com, Ashish.Kalra@....com,
        linux-kernel@...r.kernel.org, theflow@...gle.com,
        rientjes@...gle.com, pgonda@...gle.com, stable@...r.kernel.org
Subject: Re: [PATCH v3] crypto: ccp - Use kzalloc for sev ioctl interfaces to
 prevent kernel memory leak

On Tue, May 17, 2022 at 10:50:08AM -0500, Tom Lendacky wrote:
> On 5/17/22 10:39, 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 and memset the data buffer to zero in
> > sev_ioctl_do_platform_status.
> > 
> > Fixes: e799035609e15 ("crypto: ccp: Implement SEV_PEK_CSR ioctl command")
> > Fixes: 76a2b524a4b1d ("crypto: ccp: Implement SEV_PDH_CERT_EXPORT ioctl command")
> > Fixes: d6112ea0cb344 ("crypto: ccp - introduce SEV_GET_ID2 command")
> > Cc: stable@...r.kernel.org
> > Reported-by: Andy Nguyen <theflow@...gle.com>
> > Suggested-by: David Rientjes <rientjes@...gle.com>
> > Suggested-by: Peter Gonda <pgonda@...gle.com>
> > Signed-off-by: John Allen <john.allen@....com>
> > ---
> > v2:
> >    - Add fixes tags and CC stable@...r.kernel.org
> > v3:
> >    - memset data buffer to zero in sev_ioctl_do_platform_status
> > ---
> >   drivers/crypto/ccp/sev-dev.c | 10 ++++++----
> >   1 file changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> > index 6ab93dfd478a..da143cc3a8f5 100644
> > --- a/drivers/crypto/ccp/sev-dev.c
> > +++ b/drivers/crypto/ccp/sev-dev.c
> > @@ -551,6 +551,8 @@ static int sev_ioctl_do_platform_status(struct sev_issue_cmd *argp)
> >   	struct sev_user_data_status data;
> >   	int ret;
> > +	memset(&data, 0, sizeof(data));
> > +
> 
> Probably needs an additional Fixes: tag now?
> 
> Fixes: 38103671aad3 ("crypto: ccp: Use the stack and common buffer for status commands")

Thanks, Tom. I'll add the additional tag in the next revision.

Thanks,
John

> 
> Thanks,
> Tom
> 
> >   	ret = __sev_do_cmd_locked(SEV_CMD_PLATFORM_STATUS, &data, &argp->error);
> >   	if (ret)
> >   		return ret;
> > @@ -604,7 +606,7 @@ 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 +830,7 @@ 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 +949,14 @@ 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;