Re: [PATCH v5 04/14] virt: sev-guest: Add SNP guest request structure

Tom Lendacky
2023-10-30T18:16:36Z

On 10/30/23 01:36, Nikunj A Dadhania wrote:
> Add a snp_guest_req structure to simplify the function arguments. The
> structure will be used to call the SNP Guest message request API
> instead of passing a long list of parameters.
>
> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>

Some minor comments below.

> ---
> .../x86/include/asm}/sev-guest.h | 11 ++
> arch/x86/include/asm/sev.h | 8 --
> arch/x86/kernel/sev.c | 15 ++-
> drivers/virt/coco/sev-guest/sev-guest.c | 103 +++++++++++-------
> 4 files changed, 84 insertions(+), 53 deletions(-)
> rename {drivers/virt/coco/sev-guest => arch/x86/include/asm}/sev-guest.h (80%)
>
> diff --git a/drivers/virt/coco/sev-guest/sev-guest.h b/arch/x86/include/asm/sev-guest.h
> similarity index 80%
> rename from drivers/virt/coco/sev-guest/sev-guest.h
> rename to arch/x86/include/asm/sev-guest.h
> index ceb798a404d6..22ef97b55069 100644
> --- a/drivers/virt/coco/sev-guest/sev-guest.h
> +++ b/arch/x86/include/asm/sev-guest.h
> @@ -63,4 +63,15 @@ struct snp_guest_msg {
> u8 payload[4000];
> } __packed;
>
> +struct snp_guest_req {
> + void *req_buf, *resp_buf, *data;
> + size_t req_sz, resp_sz, *data_npages;

For structures like this, I find it easier to group things and keep it one
item per line, e.g.:

void *req_buf;
size_t req_sz;

void *resp_buf;
size_t resp_sz;

void *data;
size_t *data_npages;

And does data_npages have to be a pointer? It looks like you can just use
this variable as the address on the GHCB call and then set it
appropriately without all the indirection, right?

> + u64 exit_code;
> + unsigned int vmpck_id;
> + u8 msg_version;
> + u8 msg_type;
> +};
> +
> +int snp_issue_guest_request(struct snp_guest_req *req, struct snp_req_data *input,
> + struct snp_guest_request_ioctl *rio);
> #endif /* __VIRT_SEVGUEST_H__ */
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index 5b4a1ce3d368..78465a8c7dc6 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -97,8 +97,6 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
> struct snp_req_data {
> unsigned long req_gpa;
> unsigned long resp_gpa;
> - unsigned long data_gpa;
> - unsigned int data_npages;
> };
>
> struct sev_guest_platform_data {
> @@ -209,7 +207,6 @@ void snp_set_memory_private(unsigned long vaddr, unsigned long npages);
> void snp_set_wakeup_secondary_cpu(void);
> bool snp_init(struct boot_params *bp);
> void __init __noreturn snp_abort(void);
> -int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, struct snp_guest_request_ioctl *rio);
> void snp_accept_memory(phys_addr_t start, phys_addr_t end);
> u64 snp_get_unsupported_features(u64 status);
> u64 sev_get_status(void);
> @@ -233,11 +230,6 @@ static inline void snp_set_memory_private(unsigned long vaddr, unsigned long npa
> static inline void snp_set_wakeup_secondary_cpu(void) { }
> static inline bool snp_init(struct boot_params *bp) { return false; }
> static inline void snp_abort(void) { }
> -static inline int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, struct snp_guest_request_ioctl *rio)
> -{
> - return -ENOTTY;
> -}
> -

May want to mention in the commit message why this can be deleted vs changed.

> static inline void snp_accept_memory(phys_addr_t start, phys_addr_t end) { }
> static inline u64 snp_get_unsupported_features(u64 status) { return 0; }
> static inline u64 sev_get_status(void) { return 0; }
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 6395bfd87b68..f8caf0a73052 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -28,6 +28,7 @@
> #include <asm/cpu_entry_area.h>
> #include <asm/stacktrace.h>
> #include <asm/sev.h>
> +#include <asm/sev-guest.h>
> #include <asm/insn-eval.h>
> #include <asm/fpu/xcr.h>
> #include <asm/processor.h>
> @@ -2167,15 +2168,21 @@ static int __init init_sev_config(char *str)
> }
> __setup("sev=", init_sev_config);
>
> -int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, struct snp_guest_request_ioctl *rio)
> +int snp_issue_guest_request(struct snp_guest_req *req, struct snp_req_data *input,
> + struct snp_guest_request_ioctl *rio)
> {
> struct ghcb_state state;
> struct es_em_ctxt ctxt;
> unsigned long flags;
> struct ghcb *ghcb;
> + u64 exit_code;
> int ret;
>
> rio->exitinfo2 = SEV_RET_NO_FW_CALL;
> + if (!req)
> + return -EINVAL;
> +
> + exit_code = req->exit_code;
>
> /*
> * __sev_get_ghcb() needs to run with IRQs disabled because it is using
> @@ -2192,8 +2199,8 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, struct sn
> vc_ghcb_invalidate(ghcb);
>
> if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST) {
> - ghcb_set_rax(ghcb, input->data_gpa);
> - ghcb_set_rbx(ghcb, input->data_npages);
> + ghcb_set_rax(ghcb, __pa(req->data));
> + ghcb_set_rbx(ghcb, *req->data_npages);
> }
>
> ret = sev_es_ghcb_hv_call(ghcb, &ctxt, exit_code, input->req_gpa, input->resp_gpa);
> @@ -2212,7 +2219,7 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, struct sn
> case SNP_GUEST_VMM_ERR(SNP_GUEST_VMM_ERR_INVALID_LEN):
> /* Number of expected pages are returned in RBX */
> if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST) {
> - input->data_npages = ghcb_get_rbx(ghcb);
> + *req->data_npages = ghcb_get_rbx(ghcb);
> ret = -ENOSPC;
> break;
> }
> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
> index 49bafd2e9f42..5801dd52ffdf 100644
> --- a/drivers/virt/coco/sev-guest/sev-guest.c
> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
> @@ -23,8 +23,7 @@
>
> #include <asm/svm.h>
> #include <asm/sev.h>
> -
> -#include "sev-guest.h"
> +#include <asm/sev-guest.h>
>
> #define DEVICE_NAME "sev-guest"
>
> @@ -192,7 +191,7 @@ static int dec_payload(struct aesgcm_ctx *ctx, struct snp_guest_msg *msg,
> return -EBADMSG;
> }
>
> -static int verify_and_dec_payload(struct snp_guest_dev *snp_dev, void *payload, u32 sz)
> +static int verify_and_dec_payload(struct snp_guest_dev *snp_dev, struct snp_guest_req *guest_req)
> {
> struct snp_guest_msg *resp = &snp_dev->secret_response;
> struct snp_guest_msg *req = &snp_dev->secret_request;
> @@ -220,29 +219,28 @@ static int verify_and_dec_payload(struct snp_guest_dev *snp_dev, void *payload,
> * If the message size is greater than our buffer length then return
> * an error.
> */
> - if (unlikely((resp_hdr->msg_sz + ctx->authsize) > sz))
> + if (unlikely((resp_hdr->msg_sz + ctx->authsize) > guest_req->resp_sz))
> return -EBADMSG;
>
> /* Decrypt the payload */
> - return dec_payload(ctx, resp, payload, resp_hdr->msg_sz);
> + return dec_payload(ctx, resp, guest_req->resp_buf, resp_hdr->msg_sz);
> }
>
> -static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8 type,
> - void *payload, size_t sz)
> +static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, struct snp_guest_req *req)
> {
> - struct snp_guest_msg *req = &snp_dev->secret_request;
> - struct snp_guest_msg_hdr *hdr = &req->hdr;
> + struct snp_guest_msg *msg = &snp_dev->secret_request;
> + struct snp_guest_msg_hdr *hdr = &msg->hdr;
>
> - memset(req, 0, sizeof(*req));
> + memset(msg, 0, sizeof(*msg));
>
> hdr->algo = SNP_AEAD_AES_256_GCM;
> hdr->hdr_version = MSG_HDR_VER;
> hdr->hdr_sz = sizeof(*hdr);
> - hdr->msg_type = type;
> - hdr->msg_version = version;
> + hdr->msg_type = req->msg_type;
> + hdr->msg_version = req->msg_version;
> hdr->msg_seqno = seqno;
> - hdr->msg_vmpck = vmpck_id;
> - hdr->msg_sz = sz;
> + hdr->msg_vmpck = req->vmpck_id;
> + hdr->msg_sz = req->req_sz;
>
> /* Verify the sequence number is non-zero */
> if (!hdr->msg_seqno)
> @@ -251,10 +249,10 @@ static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8
> pr_debug("request [seqno %lld type %d version %d sz %d]\n",
> hdr->msg_seqno, hdr->msg_type, hdr->msg_version, hdr->msg_sz);
>
> - return __enc_payload(snp_dev->ctx, req, payload, sz);
> + return __enc_payload(snp_dev->ctx, msg, req->req_buf, req->req_sz);
> }
>
> -static int __handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
> +static int __handle_guest_request(struct snp_guest_dev *snp_dev, struct snp_guest_req *req,
> struct snp_guest_request_ioctl *rio)
> {
> unsigned long req_start = jiffies;
> @@ -269,7 +267,7 @@ static int __handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
> * sequence number must be incremented or the VMPCK must be deleted to
> * prevent reuse of the IV.
> */
> - rc = snp_issue_guest_request(exit_code, &snp_dev->input, rio);
> + rc = snp_issue_guest_request(req, &snp_dev->input, rio);
> switch (rc) {
> case -ENOSPC:
> /*
> @@ -279,8 +277,8 @@ static int __handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
> * order to increment the sequence number and thus avoid
> * IV reuse.
> */
> - override_npages = snp_dev->input.data_npages;
> - exit_code = SVM_VMGEXIT_GUEST_REQUEST;
> + override_npages = *req->data_npages;
> + req->exit_code = SVM_VMGEXIT_GUEST_REQUEST;
>
> /*
> * Override the error to inform callers the given extended
> @@ -335,15 +333,13 @@ static int __handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
> }
>
> if (override_npages)
> - snp_dev->input.data_npages = override_npages;
> + *req->data_npages = override_npages;
>
> return rc;
> }
>
> -static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
> - struct snp_guest_request_ioctl *rio, u8 type,
> - void *req_buf, size_t req_sz, void *resp_buf,
> - u32 resp_sz)
> +static int snp_send_guest_request(struct snp_guest_dev *snp_dev, struct snp_guest_req *req,
> + struct snp_guest_request_ioctl *rio)
> {
> u64 seqno;
> int rc;
> @@ -357,7 +353,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
> memset(snp_dev->response, 0, sizeof(struct snp_guest_msg));
>
> /* Encrypt the userspace provided payload in snp_dev->secret_request. */
> - rc = enc_payload(snp_dev, seqno, rio->msg_version, type, req_buf, req_sz);
> + rc = enc_payload(snp_dev, seqno, req);
> if (rc)
> return rc;
>
> @@ -368,7 +364,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
> memcpy(snp_dev->request, &snp_dev->secret_request,
> sizeof(snp_dev->secret_request));
>
> - rc = __handle_guest_request(snp_dev, exit_code, rio);
> + rc = __handle_guest_request(snp_dev, req, rio);
> if (rc) {
> if (rc == -EIO &&
> rio->exitinfo2 == SNP_GUEST_VMM_ERR(SNP_GUEST_VMM_ERR_INVALID_LEN))
> @@ -377,12 +373,11 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
> dev_alert(snp_dev->dev,
> "Detected error from ASP request. rc: %d, exitinfo2: 0x%llx\n",
> rc, rio->exitinfo2);
> -
> snp_disable_vmpck(snp_dev);
> return rc;
> }
>
> - rc = verify_and_dec_payload(snp_dev, resp_buf, resp_sz);
> + rc = verify_and_dec_payload(snp_dev, req);
> if (rc) {
> dev_alert(snp_dev->dev, "Detected unexpected decode failure from ASP. rc: %d\n", rc);
> snp_disable_vmpck(snp_dev);
> @@ -394,6 +389,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
>
> static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
> {
> + struct snp_guest_req guest_req = {0};
> struct snp_report_resp *resp;
> struct snp_report_req req;
> int rc, resp_len;
> @@ -416,9 +412,16 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
> if (!resp)
> return -ENOMEM;
>
> - rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg,
> - SNP_MSG_REPORT_REQ, &req, sizeof(req), resp->data,
> - resp_len);
> + guest_req.msg_version = arg->msg_version;
> + guest_req.msg_type = SNP_MSG_REPORT_REQ;
> + guest_req.vmpck_id = vmpck_id;
> + guest_req.req_buf = &req;
> + guest_req.req_sz = sizeof(req);
> + guest_req.resp_buf = resp->data;
> + guest_req.resp_sz = resp_len;
> + guest_req.exit_code = SVM_VMGEXIT_GUEST_REQUEST;
> +
> + rc = snp_send_guest_request(snp_dev, &guest_req, arg);
> if (rc)
> goto e_free;
>
> @@ -433,6 +436,7 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
> static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
> {
> struct snp_derived_key_resp resp = {0};
> + struct snp_guest_req guest_req = {0};
> struct snp_derived_key_req req;
> int rc, resp_len;
> /* Response data is 64 bytes and max authsize for GCM is 16 bytes. */
> @@ -455,8 +459,16 @@ static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_reque
> if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
> return -EFAULT;
>
> - rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg,
> - SNP_MSG_KEY_REQ, &req, sizeof(req), buf, resp_len);
> + guest_req.msg_version = arg->msg_version;
> + guest_req.msg_type = SNP_MSG_KEY_REQ;
> + guest_req.vmpck_id = vmpck_id;
> + guest_req.req_buf = &req;
> + guest_req.req_sz = sizeof(req);
> + guest_req.resp_buf = buf;
> + guest_req.resp_sz = resp_len;
> + guest_req.exit_code = SVM_VMGEXIT_GUEST_REQUEST;
> +
> + rc = snp_send_guest_request(snp_dev, &guest_req, arg);
> if (rc)
> return rc;
>
> @@ -472,9 +484,11 @@ static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_reque
>
> static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
> {
> + struct snp_guest_req guest_req = {0};
> struct snp_ext_report_req req;
> struct snp_report_resp *resp;
> - int ret, npages = 0, resp_len;
> + int ret, resp_len;
> + size_t npages = 0;

This becomes unnecessary if you don't define data_npages as a pointer in
the snp_guest_req structure.

Thanks,
Tom

>
> lockdep_assert_held(&snp_dev->cmd_mutex);
>
> @@ -514,14 +528,22 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
> if (!resp)
> return -ENOMEM;
>
> - snp_dev->input.data_npages = npages;
> - ret = handle_guest_request(snp_dev, SVM_VMGEXIT_EXT_GUEST_REQUEST, arg,
> - SNP_MSG_REPORT_REQ, &req.data,
> - sizeof(req.data), resp->data, resp_len);
> + guest_req.msg_version = arg->msg_version;
> + guest_req.msg_type = SNP_MSG_REPORT_REQ;
> + guest_req.vmpck_id = vmpck_id;
> + guest_req.req_buf = &req.data;
> + guest_req.req_sz = sizeof(req.data);
> + guest_req.resp_buf = resp->data;
> + guest_req.resp_sz = resp_len;
> + guest_req.exit_code = SVM_VMGEXIT_EXT_GUEST_REQUEST;
> + guest_req.data = snp_dev->certs_data;
> + guest_req.data_npages = &npages;
> +
> + ret = snp_send_guest_request(snp_dev, &guest_req, arg);
>
> /* If certs length is invalid then copy the returned length */
> if (arg->vmm_error == SNP_GUEST_VMM_ERR_INVALID_LEN) {
> - req.certs_len = snp_dev->input.data_npages << PAGE_SHIFT;
> + req.certs_len = npages << PAGE_SHIFT;
>
> if (copy_to_user((void __user *)arg->req_data, &req, sizeof(req)))
> ret = -EFAULT;
> @@ -530,7 +552,7 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
> if (ret)
> goto e_free;
>
> - if (npages &&
> + if (npages && req.certs_len &&
> copy_to_user((void __user *)req.certs_address, snp_dev->certs_data,
> req.certs_len)) {
> ret = -EFAULT;
> @@ -734,7 +756,6 @@ static int __init sev_guest_probe(struct platform_device *pdev)
> /* initial the input address for guest request */
> snp_dev->input.req_gpa = __pa(snp_dev->request);
> snp_dev->input.resp_gpa = __pa(snp_dev->response);
> - snp_dev->input.data_gpa = __pa(snp_dev->certs_data);
>
> ret = misc_register(misc);
> if (ret)