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

    >
    > 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
    >


    --
    -Dionna Glaze, PhD (she/her)

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