Re: [PATCH v5 05/14] virt: sev-guest: Add vmpck_id to snp_guest_dev struct

Tom Lendacky
2023-10-30T17:12:22Z

On 10/30/23 11:16, Dionna Amalie Glaze wrote:
> On Sun, Oct 29, 2023 at 11:38 PM Nikunj A Dadhania <nikunj@amd.com> wrote:
>>
>> Drop vmpck and os_area_msg_seqno pointers so that secret page layout
>> does not need to be exposed to the sev-guest driver after the rework.
>> Instead, add helper APIs to access vmpck and os_area_msg_seqno when
>> needed.
>>
>> Also, change function is_vmpck_empty() to snp_is_vmpck_empty() in
>> preparation for moving to sev.c.
>>
>> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
>> ---
>> drivers/virt/coco/sev-guest/sev-guest.c | 85 ++++++++++++-------------
>> 1 file changed, 42 insertions(+), 43 deletions(-)
>>
>> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
>> index 5801dd52ffdf..4dd094c73e2f 100644
>> --- a/drivers/virt/coco/sev-guest/sev-guest.c
>> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
>> @@ -50,8 +50,7 @@ struct snp_guest_dev {
>>
>> struct snp_secrets_page_layout *layout;
>> struct snp_req_data input;
>> - u32 *os_area_msg_seqno;
>> - u8 *vmpck;
>> + unsigned int vmpck_id;
>> };
>>
>> static u32 vmpck_id;
>> @@ -61,14 +60,22 @@ MODULE_PARM_DESC(vmpck_id, "The VMPCK ID to use when communicating with the PSP.
>> /* Mutex to serialize the shared buffer access and command handling. */
>> static DEFINE_MUTEX(snp_cmd_mutex);
>>
>> -static bool is_vmpck_empty(struct snp_guest_dev *snp_dev)
>> +static inline u8 *snp_get_vmpck(struct snp_guest_dev *snp_dev)
>> {
>> - char zero_key[VMPCK_KEY_LEN] = {0};
>> + return snp_dev->layout->vmpck0 + snp_dev->vmpck_id * VMPCK_KEY_LEN;
>> +}
>>
>> - if (snp_dev->vmpck)
>> - return !memcmp(snp_dev->vmpck, zero_key, VMPCK_KEY_LEN);
>> +static inline u32 *snp_get_os_area_msg_seqno(struct snp_guest_dev *snp_dev)
>> +{
>> + return &snp_dev->layout->os_area.msg_seqno_0 + snp_dev->vmpck_id;
>> +}
>>
>> - return true;
>> +static bool snp_is_vmpck_empty(struct snp_guest_dev *snp_dev)
>> +{
>> + char zero_key[VMPCK_KEY_LEN] = {0};
>> + u8 *key = snp_get_vmpck(snp_dev);
>> +
>> + return !memcmp(key, zero_key, VMPCK_KEY_LEN);
>> }
>>
>> /*
>> @@ -90,20 +97,22 @@ static bool is_vmpck_empty(struct snp_guest_dev *snp_dev)
>> */
>> static void snp_disable_vmpck(struct snp_guest_dev *snp_dev)
>> {
>> + u8 *key = snp_get_vmpck(snp_dev);
>> +
>> dev_alert(snp_dev->dev, "Disabling vmpck_id %d to prevent IV reuse.\n",
>> - vmpck_id);
>> - memzero_explicit(snp_dev->vmpck, VMPCK_KEY_LEN);
>> - snp_dev->vmpck = NULL;
>> + snp_dev->vmpck_id);
>> + memzero_explicit(key, VMPCK_KEY_LEN);
>> }
>
> We disable the VMPCK because we believe the guest to be under attack,
> but this only clears a single key. Shouldn't we clear all VMPCK keys
> in the secrets page for good measure? If at VMPCK > 0, most likely the
> 0..VMPCK-1 keys have been zeroed by whatever was prior in the boot
> stack, but still better to be safe.

Doing that would be a separate patch series and isn't appropriate here.

Thanks,
Tom

>
>>
>> static inline u64 __snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
>> {
>> + u32 *os_area_msg_seqno = snp_get_os_area_msg_seqno(snp_dev);
>> u64 count;
>>
>> lockdep_assert_held(&snp_dev->cmd_mutex);
>>
>> /* Read the current message sequence counter from secrets pages */
>> - count = *snp_dev->os_area_msg_seqno;
>> + count = *os_area_msg_seqno;
>>
>> return count + 1;
>> }
>> @@ -131,11 +140,13 @@ static u64 snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
>>
>> static void snp_inc_msg_seqno(struct snp_guest_dev *snp_dev)
>> {
>> + u32 *os_area_msg_seqno = snp_get_os_area_msg_seqno(snp_dev);
>> +
>> /*
>> * The counter is also incremented by the PSP, so increment it by 2
>> * and save in secrets page.
>> */
>> - *snp_dev->os_area_msg_seqno += 2;
>> + *os_area_msg_seqno += 2;
>> }
>>
>> static inline struct snp_guest_dev *to_snp_dev(struct file *file)
>> @@ -145,15 +156,22 @@ static inline struct snp_guest_dev *to_snp_dev(struct file *file)
>> return container_of(dev, struct snp_guest_dev, misc);
>> }
>>
>> -static struct aesgcm_ctx *snp_init_crypto(u8 *key, size_t keylen)
>> +static struct aesgcm_ctx *snp_init_crypto(struct snp_guest_dev *snp_dev)
>> {
>> struct aesgcm_ctx *ctx;
>> + u8 *key;
>> +
>> + if (snp_is_vmpck_empty(snp_dev)) {
>> + pr_err("SNP: vmpck id %d is null\n", snp_dev->vmpck_id);
>> + return NULL;
>> + }
>>
>> ctx = kzalloc(sizeof(*ctx), GFP_KERNEL_ACCOUNT);
>> if (!ctx)
>> return NULL;
>>
>> - if (aesgcm_expandkey(ctx, key, keylen, AUTHTAG_LEN)) {
>> + key = snp_get_vmpck(snp_dev);
>> + if (aesgcm_expandkey(ctx, key, VMPCK_KEY_LEN, AUTHTAG_LEN)) {
>> pr_err("SNP: crypto init failed\n");
>> kfree(ctx);
>> return NULL;
>> @@ -586,7 +604,7 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
>> mutex_lock(&snp_dev->cmd_mutex);
>>
>> /* Check if the VMPCK is not empty */
>> - if (is_vmpck_empty(snp_dev)) {
>> + if (snp_is_vmpck_empty(snp_dev)) {
>> dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
>> mutex_unlock(&snp_dev->cmd_mutex);
>> return -ENOTTY;
>> @@ -656,32 +674,14 @@ static const struct file_operations snp_guest_fops = {
>> .unlocked_ioctl = snp_guest_ioctl,
>> };
>>
>> -static u8 *get_vmpck(int id, struct snp_secrets_page_layout *layout, u32 **seqno)
>> +bool snp_assign_vmpck(struct snp_guest_dev *dev, int vmpck_id)
>> {
>> - u8 *key = NULL;
>> + if (WARN_ON(vmpck_id > 3))
>> + return false;
>
> The vmpck_id is an int for some reason, so < 0 is also a problem. Can
> we not use unsigned int?
>
>>
>> - switch (id) {
>> - case 0:
>> - *seqno = &layout->os_area.msg_seqno_0;
>> - key = layout->vmpck0;
>> - break;
>> - case 1:
>> - *seqno = &layout->os_area.msg_seqno_1;
>> - key = layout->vmpck1;
>> - break;
>> - case 2:
>> - *seqno = &layout->os_area.msg_seqno_2;
>> - key = layout->vmpck2;
>> - break;
>> - case 3:
>> - *seqno = &layout->os_area.msg_seqno_3;
>> - key = layout->vmpck3;
>> - break;
>> - default:
>> - break;
>> - }
>> + dev->vmpck_id = vmpck_id;
>>
>> - return key;
>> + return true;
>> }
>>
>> static int __init sev_guest_probe(struct platform_device *pdev)
>> @@ -713,14 +713,14 @@ static int __init sev_guest_probe(struct platform_device *pdev)
>> goto e_unmap;
>>
>> ret = -EINVAL;
>> - snp_dev->vmpck = get_vmpck(vmpck_id, layout, &snp_dev->os_area_msg_seqno);
>> - if (!snp_dev->vmpck) {
>> + snp_dev->layout = layout;
>> + if (!snp_assign_vmpck(snp_dev, vmpck_id)) {
>> dev_err(dev, "invalid vmpck id %d\n", vmpck_id);
>> goto e_unmap;
>> }
>>
>> /* Verify that VMPCK is not zero. */
>> - if (is_vmpck_empty(snp_dev)) {
>> + if (snp_is_vmpck_empty(snp_dev)) {
>> dev_err(dev, "vmpck id %d is null\n", vmpck_id);
>> goto e_unmap;
>> }
>> @@ -728,7 +728,6 @@ static int __init sev_guest_probe(struct platform_device *pdev)
>> mutex_init(&snp_dev->cmd_mutex);
>> platform_set_drvdata(pdev, snp_dev);
>> snp_dev->dev = dev;
>> - snp_dev->layout = layout;
>>
>> /* Allocate the shared page used for the request and response message. */
>> snp_dev->request = alloc_shared_pages(dev, sizeof(struct snp_guest_msg));
>> @@ -744,7 +743,7 @@ static int __init sev_guest_probe(struct platform_device *pdev)
>> goto e_free_response;
>>
>> ret = -EIO;
>> - snp_dev->ctx = snp_init_crypto(snp_dev->vmpck, VMPCK_KEY_LEN);
>> + snp_dev->ctx = snp_init_crypto(snp_dev);
>> if (!snp_dev->ctx)
>> goto e_free_cert_data;
>>
>> --
>> 2.34.1
>>
>
>