[PATCH v12 0/3] Add throttling detection to sev-guest

[PATCH v12 0/3] Add throttling detection to sev-guest

[Dionna Glaze]

The guest request synchronous API from SEV-SNP VMs to the host's security
processor consumes a global resource. For this reason, AMD's docs
recommend that the host implements a throttling mechanism. In order for
the guest to know it's been throttled and should try its request again,
we need some good-faith communication from the host that the request
has been throttled.

These patches work with the existing /dev/sev-guest ABI to detect a
throttling code.

Changes from v11:
  * Squashed all type changing patches into 1 that modifies both sev-guest
    and x86/kernel/sev.c.
  * Removed fw_err field from sev-guest command struct (renamed exitinfo2).
Changes from v10:
  * Added sev_guestreq_err_t typedef early in chain to change a signature
    acress x86/sev and virt/coco/sev-guest in a single change. This makes
    all patches build. I have 3 cleanup patches to change the type and
    subsequently remove the typedef.
  * Changed exitinfo2 initial undefined value back to 0xff since Thomas
    indicated that a firmware error is only 16 bits.
Changes from v9:
  * Rebased on v6.2-rc3
Changes from v8:
  * Added documentation changes.
  * Changed commit messages to use passive voice.
  * Simplified control flow for __sev_platform_init_locked.
Changes from v7:
  * Replaced handle_guest_request arguments msg_ver and fw_err with a
    pointer to the snp_guest_request_ioctl argument struct.
Changes from v6:
  * Rebased on the IV reuse fix patch
  * renamed rate_hz to rate_s and fixed its MODULE_PARM_DESC to use the
    correct variable name.
  * Changed sleep_timeout_interrutible (not defined) to
    schedule_timeout_interruptible.
Changes from v5:
  * Fixed commit prefix text
  * Added all get_maintainers.pl folks to commits' Cc tags
  * Changed SET_RET_NO_FW_CALL commit's metadata to show pgonda signs
    off and is the author.
Changes from v4:
  * Clarified comment on SEV_RET_NO_FW_CALL
  * Changed ratelimit loop to use sleep_timeout_interruptible
Changes from v3:
  * sev-guest ratelimits itself to one request twice a second.
  * Fixed a type signature to use u64 instead of unsigned int
  * Set *exitinfo2 unconditionally after the ghcb_hv_call.
Changes from v2:
  * Codified the non-firmware-call firmware error code as (u32)-1.
  * Changed sev_issue_guest_request unsigned long *fw_err argument to
    u64 *exitinfo2 to more accurately and type-safely describe the
    value that it outputs.
  * Changed sev_issue_guest_request to always set its exitinfo2
    argument to either the non-firmware-call error code, the
    EXIT_INFO_2 returned from the VMM if the request failed, or 0 on
    success. This fixes a bug that returned uninitialized kernel stack
    memory to the user when there is no error.
  * Changed the throttle behavior to retry in the driver instead of
    returning -EAGAIN, due to possible message sequence number reuse
    on different message contents.

Changes from v1:
  * Changed throttle error code to 2

Dionna Glaze (2):
  x86/sev: Change snp_guest_issue_request's fw_err
  virt: sev-guest: interpret VMM errors from guest request

Peter Gonda (1):
  crypto: ccp - Name -1 return value as SEV_RET_NO_FW_CALL

 Documentation/virt/coco/sev-guest.rst   | 21 ++++---
 arch/x86/include/asm/sev-common.h       |  3 -
 arch/x86/include/asm/sev.h              |  4 +-
 arch/x86/kernel/sev.c                   | 13 +++--
 drivers/crypto/ccp/sev-dev.c            | 22 ++++---
 drivers/virt/coco/sev-guest/sev-guest.c | 77 +++++++++++++++++--------
 include/uapi/linux/psp-sev.h            |  7 +++
 include/uapi/linux/sev-guest.h          | 18 +++++-
 8 files changed, 114 insertions(+), 51 deletions(-)

-- 
2.39.0.246.g2a6d74b583-goog

[PATCH v12 1/3] crypto: ccp - Name -1 return value as SEV_RET_NO_FW_CALL

[Dionna Glaze]

From: Peter Gonda <pgonda@google.com>

The PSP can return a "firmware error" code of -1 in circumstances where
the PSP is not actually called. To make this protocol unambiguous, the
value is named SEV_RET_NO_FW_CALL.

Cc: Thomas Lendacky <Thomas.Lendacky@amd.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Andy Lutomirsky <luto@kernel.org>
Cc: John Allen <john.allen@amd.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Borislav Petkov <Borislav.Petkov@amd.com>

Signed-off-by: Peter Gonda <pgonda@google.com>
Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
---
 Documentation/virt/coco/sev-guest.rst |  2 +-
 drivers/crypto/ccp/sev-dev.c          | 22 ++++++++++++++--------
 include/uapi/linux/psp-sev.h          |  7 +++++++
 3 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/Documentation/virt/coco/sev-guest.rst b/Documentation/virt/coco/sev-guest.rst
index bf593e88cfd9..e76393e389eb 100644
--- a/Documentation/virt/coco/sev-guest.rst
+++ b/Documentation/virt/coco/sev-guest.rst
@@ -41,7 +41,7 @@ The guest ioctl should be issued on a file descriptor of the /dev/sev-guest devi
 The ioctl accepts struct snp_user_guest_request. The input and output structure is
 specified through the req_data and resp_data field respectively. If the ioctl fails
 to execute due to a firmware error, then fw_err code will be set otherwise the
-fw_err will be set to 0x00000000000000ff.
+fw_err will be set to 0x00000000ffffffff, i.e., the lower 32-bits are -1.
 
 The firmware checks that the message sequence counter is one greater than
 the guests message sequence counter. If guest driver fails to increment message
diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 06fc7156c04f..ac205f78a595 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -440,12 +440,19 @@ static int __sev_init_ex_locked(int *error)
 	return __sev_do_cmd_locked(SEV_CMD_INIT_EX, &data, error);
 }
 
+static inline int __sev_do_init_locked(int *psp_ret)
+{
+	if (sev_init_ex_buffer)
+		return __sev_init_ex_locked(psp_ret);
+	else
+		return __sev_init_locked(psp_ret);
+}
+
 static int __sev_platform_init_locked(int *error)
 {
 	struct psp_device *psp = psp_master;
 	struct sev_device *sev;
-	int rc = 0, psp_ret = -1;
-	int (*init_function)(int *error);
+	int rc = 0, psp_ret = SEV_RET_NO_FW_CALL;
 
 	if (!psp || !psp->sev_data)
 		return -ENODEV;
@@ -456,15 +463,12 @@ static int __sev_platform_init_locked(int *error)
 		return 0;
 
 	if (sev_init_ex_buffer) {
-		init_function = __sev_init_ex_locked;
 		rc = sev_read_init_ex_file();
 		if (rc)
 			return rc;
-	} else {
-		init_function = __sev_init_locked;
 	}
 
-	rc = init_function(&psp_ret);
+	rc = __sev_do_init_locked(&psp_ret);
 	if (rc && psp_ret == SEV_RET_SECURE_DATA_INVALID) {
 		/*
 		 * Initialization command returned an integrity check failure
@@ -473,9 +477,11 @@ static int __sev_platform_init_locked(int *error)
 		 * initialization function should succeed by replacing the state
 		 * with a reset state.
 		 */
-		dev_err(sev->dev, "SEV: retrying INIT command because of SECURE_DATA_INVALID error. Retrying once to reset PSP SEV state.");
-		rc = init_function(&psp_ret);
+		dev_err(sev->dev,
+"SEV: retrying INIT command because of SECURE_DATA_INVALID error. Retrying once to reset PSP SEV state.");
+		rc = __sev_do_init_locked(&psp_ret);
 	}
+
 	if (error)
 		*error = psp_ret;
 
diff --git a/include/uapi/linux/psp-sev.h b/include/uapi/linux/psp-sev.h
index 91b4c63d5cbf..e8cfb8bde0d7 100644
--- a/include/uapi/linux/psp-sev.h
+++ b/include/uapi/linux/psp-sev.h
@@ -36,6 +36,13 @@ enum {
  * SEV Firmware status code
  */
 typedef enum {
+	/*
+	 * This error code is not in the SEV spec but is added to convey that
+	 * there was an error that prevented the SEV Firmware from being called.
+	 * The SEV API error codes are 16 bits, so the -1 value will not overlap
+	 * with possible values from the specification.
+	 */
+	SEV_RET_NO_FW_CALL = -1,
 	SEV_RET_SUCCESS = 0,
 	SEV_RET_INVALID_PLATFORM_STATE,
 	SEV_RET_INVALID_GUEST_STATE,
-- 
2.39.0.246.g2a6d74b583-goog

[PATCH v12 2/3] x86/sev: Change snp_guest_issue_request's fw_err

[Dionna Glaze]

The GHCB specification declares that the firmware error value for a
guest request will be stored in the lower 32 bits of EXIT_INFO_2.
The upper 32 bits are for the VMM's own error code. The fw_err argument
is thus a misnomer, and callers will need access to all 64 bits.

The type of unsigned long also causes problems, since sw_exit_info2 is
u64 (unsigned long long) vs the argument's unsigned long*. This type
is changed for issuing the guest request. The ioctl command struct's
error field is passed directly instead of a local variable, since an
incomplete guest request may not set the error code, and uninitialized
stack memory would be written back to user space.

The firmware might not even be called, so the call is bookended with
the no firmware call error and clearing the error.

Since the "fw_err" field is really exitinfo2 split into the upper bits'
vmm error code and lower bits' firmware error code, sev-guest.h is
updated to represent the 64 bit value as a union.

Cc: Tom Lendacky <Thomas.Lendacky@amd.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Peter Gonda <pgonda@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <Borislav.Petkov@amd.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Venu Busireddy <venu.busireddy@oracle.com>
Cc: Michael Roth <michael.roth@amd.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Michael Sterritt <sterritt@google.com>

Fixes: d5af44dde546 ("x86/sev: Provide support for SNP guest request NAEs")
Reviewed-by: Tom Lendacky <Thomas.Lendacky@amd.com>
Reviewed-by: Borislav Petkov <Borislav.Petkov@amd.com>
Reviewed-by: Peter Gonda <pgonda@google.com>
Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
---
 arch/x86/include/asm/sev-common.h       |  3 --
 arch/x86/include/asm/sev.h              |  4 +--
 arch/x86/kernel/sev.c                   | 13 ++++---
 drivers/virt/coco/sev-guest/sev-guest.c | 46 ++++++++++++-------------
 include/uapi/linux/sev-guest.h          | 18 ++++++++--
 5 files changed, 48 insertions(+), 36 deletions(-)

diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index b8357d6ecd47..0759af9b1acf 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -128,9 +128,6 @@ struct snp_psc_desc {
 	struct psc_entry entries[VMGEXIT_PSC_MAX_ENTRY];
 } __packed;
 
-/* Guest message request error code */
-#define SNP_GUEST_REQ_INVALID_LEN	BIT_ULL(32)
-
 #define GHCB_MSR_TERM_REQ		0x100
 #define GHCB_MSR_TERM_REASON_SET_POS	12
 #define GHCB_MSR_TERM_REASON_SET_MASK	0xf
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index ebc271bb6d8e..05de34d10d89 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -196,7 +196,7 @@ void snp_set_memory_private(unsigned long vaddr, unsigned int 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, unsigned long *fw_err);
+int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, u64 *exitinfo2);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }
@@ -217,7 +217,7 @@ 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,
-					  unsigned long *fw_err)
+					  u64 *exitinfo2)
 {
 	return -ENOTTY;
 }
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 679026a640ef..82aa81fafb71 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -22,6 +22,8 @@
 #include <linux/efi.h>
 #include <linux/platform_device.h>
 #include <linux/io.h>
+#include <linux/psp-sev.h>
+#include <uapi/linux/sev-guest.h>
 
 #include <asm/cpu_entry_area.h>
 #include <asm/stacktrace.h>
@@ -2175,7 +2177,7 @@ 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, unsigned long *fw_err)
+int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, u64 *exitinfo2)
 {
 	struct ghcb_state state;
 	struct es_em_ctxt ctxt;
@@ -2186,9 +2188,11 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned
 	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
 		return -ENODEV;
 
-	if (!fw_err)
+	if (!exitinfo2)
 		return -EINVAL;
 
+	*exitinfo2 = SEV_RET_NO_FW_CALL;
+
 	/*
 	 * __sev_get_ghcb() needs to run with IRQs disabled because it is using
 	 * a per-CPU GHCB.
@@ -2212,14 +2216,13 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned
 	if (ret)
 		goto e_put;
 
+	*exitinfo2 = ghcb->save.sw_exit_info_2;
 	if (ghcb->save.sw_exit_info_2) {
 		/* Number of expected pages are returned in RBX */
 		if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST &&
-		    ghcb->save.sw_exit_info_2 == SNP_GUEST_REQ_INVALID_LEN)
+			ghcb->save.sw_exit_info_2 == SNP_GUEST_VMM_ERR(SNP_GUEST_VMM_ERR_INVALID_LEN))
 			input->data_npages = ghcb_get_rbx(ghcb);
 
-		*fw_err = ghcb->save.sw_exit_info_2;
-
 		ret = -EIO;
 	}
 
diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index 4ec4174e05a3..ed6fc14f6b00 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -318,11 +318,11 @@ static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8
 	return __enc_payload(snp_dev, req, payload, sz);
 }
 
-static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, int msg_ver,
-				u8 type, void *req_buf, size_t req_sz, void *resp_buf,
-				u32 resp_sz, __u64 *fw_err)
+static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
+				struct snp_guest_request_ioctl *arg,
+				u8 type, void *req_buf, size_t req_sz,
+				void *resp_buf, u32 resp_sz)
 {
-	unsigned long err;
 	u64 seqno;
 	int rc;
 
@@ -334,7 +334,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 	memset(snp_dev->response, 0, sizeof(struct snp_guest_msg));
 
 	/* Encrypt the userspace provided payload */
-	rc = enc_payload(snp_dev, seqno, msg_ver, type, req_buf, req_sz);
+	rc = enc_payload(snp_dev, seqno, arg->msg_version, type, req_buf, req_sz);
 	if (rc)
 		return rc;
 
@@ -344,7 +344,8 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 	 * 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, &err);
+	rc = snp_issue_guest_request(exit_code, &snp_dev->input,
+				     &arg->exitinfo2);
 
 	/*
 	 * If the extended guest request fails due to having too small of a
@@ -353,7 +354,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 	 * and thus avoid IV reuse.
 	 */
 	if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST &&
-	    err == SNP_GUEST_REQ_INVALID_LEN) {
+	    arg->vmm_error == SNP_GUEST_VMM_ERR_INVALID_LEN) {
 		const unsigned int certs_npages = snp_dev->input.data_npages;
 
 		exit_code = SVM_VMGEXIT_GUEST_REQUEST;
@@ -366,24 +367,22 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 		 * of the VMPCK and the error code being propagated back to the
 		 * user as an ioctl() return code.
 		 */
-		rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
+		rc = snp_issue_guest_request(exit_code, &snp_dev->input,
+					     &arg->exitinfo2);
 
 		/*
 		 * Override the error to inform callers the given extended
 		 * request buffer size was too small and give the caller the
 		 * required buffer size.
 		 */
-		err = SNP_GUEST_REQ_INVALID_LEN;
+		arg->vmm_error = SNP_GUEST_VMM_ERR_INVALID_LEN;
 		snp_dev->input.data_npages = certs_npages;
 	}
 
-	if (fw_err)
-		*fw_err = err;
-
 	if (rc) {
 		dev_alert(snp_dev->dev,
-			  "Detected error from ASP request. rc: %d, fw_err: %llu\n",
-			  rc, *fw_err);
+			  "Detected error from ASP request. rc: %d, exitinfo2: %llu\n",
+			  rc, arg->exitinfo2);
 		goto disable_vmpck;
 	}
 
@@ -430,9 +429,9 @@ 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->msg_version,
+	rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg,
 				  SNP_MSG_REPORT_REQ, &req, sizeof(req), resp->data,
-				  resp_len, &arg->fw_err);
+				  resp_len);
 	if (rc)
 		goto e_free;
 
@@ -470,9 +469,8 @@ 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->msg_version,
-				  SNP_MSG_KEY_REQ, &req, sizeof(req), buf, resp_len,
-				  &arg->fw_err);
+	rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg,
+				  SNP_MSG_KEY_REQ, &req, sizeof(req), buf, resp_len);
 	if (rc)
 		return rc;
 
@@ -532,12 +530,12 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
 		return -ENOMEM;
 
 	snp_dev->input.data_npages = npages;
-	ret = handle_guest_request(snp_dev, SVM_VMGEXIT_EXT_GUEST_REQUEST, arg->msg_version,
+	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, &arg->fw_err);
+				   sizeof(req.data), resp->data, resp_len);
 
 	/* If certs length is invalid then copy the returned length */
-	if (arg->fw_err == SNP_GUEST_REQ_INVALID_LEN) {
+	if (arg->vmm_error == SNP_GUEST_VMM_ERR_INVALID_LEN) {
 		req.certs_len = snp_dev->input.data_npages << PAGE_SHIFT;
 
 		if (copy_to_user((void __user *)arg->req_data, &req, sizeof(req)))
@@ -572,7 +570,7 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
 	if (copy_from_user(&input, argp, sizeof(input)))
 		return -EFAULT;
 
-	input.fw_err = 0xff;
+	input.exitinfo2 = 0xff;
 
 	/* Message version must be non-zero */
 	if (!input.msg_version)
@@ -603,7 +601,7 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
 
 	mutex_unlock(&snp_cmd_mutex);
 
-	if (input.fw_err && copy_to_user(argp, &input, sizeof(input)))
+	if (input.exitinfo2 && copy_to_user(argp, &input, sizeof(input)))
 		return -EFAULT;
 
 	return ret;
diff --git a/include/uapi/linux/sev-guest.h b/include/uapi/linux/sev-guest.h
index 256aaeff7e65..2aa39112cf8d 100644
--- a/include/uapi/linux/sev-guest.h
+++ b/include/uapi/linux/sev-guest.h
@@ -52,8 +52,14 @@ struct snp_guest_request_ioctl {
 	__u64 req_data;
 	__u64 resp_data;
 
-	/* firmware error code on failure (see psp-sev.h) */
-	__u64 fw_err;
+	/* bits[63:32]: VMM error code, bits[31:0] firmware error code (see psp-sev.h) */
+	union {
+		__u64 exitinfo2;
+		struct {
+			__u32 fw_error;
+			__u32 vmm_error;
+		};
+	};
 };
 
 struct snp_ext_report_req {
@@ -77,4 +83,12 @@ struct snp_ext_report_req {
 /* Get SNP extended report as defined in the GHCB specification version 2. */
 #define SNP_GET_EXT_REPORT _IOWR(SNP_GUEST_REQ_IOC_TYPE, 0x2, struct snp_guest_request_ioctl)
 
+/* Guest message request EXIT_INFO_2 constants */
+#define SNP_GUEST_FW_ERR_MASK		GENMASK_ULL(31, 0)
+#define SNP_GUEST_VMM_ERR_SHIFT		32
+#define SNP_GUEST_VMM_ERR(x)		(((u64)x) << SNP_GUEST_VMM_ERR_SHIFT)
+
+#define SNP_GUEST_VMM_ERR_INVALID_LEN	1
+#define SNP_GUEST_VMM_ERR_BUSY		2
+
 #endif /* __UAPI_LINUX_SEV_GUEST_H_ */
-- 
2.39.0.246.g2a6d74b583-goog

Re: [PATCH v12 2/3] x86/sev: Change snp_guest_issue_request's fw_err

[Borislav Petkov]

On Fri, Jan 20, 2023 at 09:48:55PM +0000, Dionna Glaze wrote:
> The GHCB specification declares that the firmware error value for a
> guest request will be stored in the lower 32 bits of EXIT_INFO_2.
> The upper 32 bits are for the VMM's own error code. The fw_err argument
> is thus a misnomer, and callers will need access to all 64 bits.
> 
> The type of unsigned long also causes problems, since sw_exit_info2 is
> u64 (unsigned long long) vs the argument's unsigned long*. This type
> is changed for issuing the guest request. The ioctl command struct's
> error field is passed directly instead of a local variable, since an
> incomplete guest request may not set the error code, and uninitialized
> stack memory would be written back to user space.
> 
> The firmware might not even be called, so the call is bookended with
> the no firmware call error and clearing the error.
> 
> Since the "fw_err" field is really exitinfo2 split into the upper bits'
> vmm error code and lower bits' firmware error code, sev-guest.h is
> updated to represent the 64 bit value as a union.
> 
> Cc: Tom Lendacky <Thomas.Lendacky@amd.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Joerg Roedel <jroedel@suse.de>
> Cc: Peter Gonda <pgonda@google.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <Borislav.Petkov@amd.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Venu Busireddy <venu.busireddy@oracle.com>
> Cc: Michael Roth <michael.roth@amd.com>
> Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
> Cc: Michael Sterritt <sterritt@google.com>
> 
> Fixes: d5af44dde546 ("x86/sev: Provide support for SNP guest request NAEs")
> Reviewed-by: Tom Lendacky <Thomas.Lendacky@amd.com>

> Reviewed-by: Borislav Petkov <Borislav.Petkov@amd.com>

Please don't add tags you haven't received. Especially a Reviewed-by. Have a
look here what they mean, if unsure:

Documentation/process/submitting-patches.rst

I've removed it - you don't have to resend just because of that.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v12 2/3] x86/sev: Change snp_guest_issue_request's fw_err

[Borislav Petkov]

On Fri, Jan 20, 2023 at 09:48:55PM +0000, Dionna Glaze wrote:
> Since the "fw_err" field is really exitinfo2 split into the upper bits'
> vmm error code and lower bits' firmware error code, sev-guest.h is
> updated to represent the 64 bit value as a union.

Yah, documentation needs update too:

diff --git a/Documentation/virt/coco/sev-guest.rst b/Documentation/virt/coco/sev-guest.rst
index 4f0dcc1d16e8..4f9df24b829f 100644
--- a/Documentation/virt/coco/sev-guest.rst
+++ b/Documentation/virt/coco/sev-guest.rst
@@ -57,9 +57,16 @@ counter (e.g. counter overflow), then -EIO will be returned.
                 __u64 req_data;
                 __u64 resp_data;
 
-                /* firmware error code on failure (see psp-sev.h) */
-                __u64 fw_err;
-        };
+                /* bits[63:32]: VMM error code, bits[31:0] firmware error code (see psp-sev.h) */
+                union {
+                        __u64 exitinfo2;
+                        struct {
+                                __u32 fw_error;
+                                __u32 vmm_error;
+                        };
+                };
+	};
+
 
 2.1 SNP_GET_REPORT
 ------------------

/me goes and looks at patch 3...

Yap, that change adding the union should all belong together in a single patch.

> @@ -366,24 +367,22 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
>  		 * of the VMPCK and the error code being propagated back to the
>  		 * user as an ioctl() return code.
>  		 */
> -		rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
> +		rc = snp_issue_guest_request(exit_code, &snp_dev->input,
> +					     &arg->exitinfo2);
>  
>  		/*
>  		 * Override the error to inform callers the given extended
>  		 * request buffer size was too small and give the caller the
>  		 * required buffer size.
>  		 */
> -		err = SNP_GUEST_REQ_INVALID_LEN;
> +		arg->vmm_error = SNP_GUEST_VMM_ERR_INVALID_LEN;
>  		snp_dev->input.data_npages = certs_npages;
>  	}
>  
> -	if (fw_err)
> -		*fw_err = err;
> -
>  	if (rc) {
>  		dev_alert(snp_dev->dev,
> -			  "Detected error from ASP request. rc: %d, fw_err: %llu\n",
> -			  rc, *fw_err);
> +			  "Detected error from ASP request. rc: %d, exitinfo2: %llu\n",
> +			  rc, arg->exitinfo2);

I guess that's better off dumped in binary now:

diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index d4973d2dbc24..a5d6ea3eebe9 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -380,7 +380,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
 
 	if (rc) {
 		dev_alert(snp_dev->dev,
-			  "Detected error from ASP request. rc: %d, exitinfo2: %llu\n",
+			  "Detected error from ASP request. rc: %d, exitinfo2: 0x%llx\n",
 			  rc, arg->exitinfo2);
 		goto disable_vmpck;
 	}

Anyway, that's a lot of changes for a fix which needs to go to stable. I don't
mind them but not in a minimal fix.

So how is this for a minimal fix to go in now, ontop of your first patch? The
cleanups can then go later...

---
diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index 4ec4174e05a3..20b560a45bc1 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -322,7 +322,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 				u8 type, void *req_buf, size_t req_sz, void *resp_buf,
 				u32 resp_sz, __u64 *fw_err)
 {
-	unsigned long err;
+	unsigned long err = SEV_RET_NO_FW_CALL;
 	u64 seqno;
 	int rc;
 

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v12 2/3] x86/sev: Change snp_guest_issue_request's fw_err

[Dionna Amalie Glaze]

>
> Anyway, that's a lot of changes for a fix which needs to go to stable. I don't
> mind them but not in a minimal fix.
>

> So how is this for a minimal fix to go in now, ontop of your first patch? The
> cleanups can then go later...
>
> ---
> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
> index 4ec4174e05a3..20b560a45bc1 100644
> --- a/drivers/virt/coco/sev-guest/sev-guest.c
> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
> @@ -322,7 +322,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
>                                 u8 type, void *req_buf, size_t req_sz, void *resp_buf,
>                                 u32 resp_sz, __u64 *fw_err)
>  {
> -       unsigned long err;
> +       unsigned long err = SEV_RET_NO_FW_CALL;
>         u64 seqno;
>         int rc;
>

This isn't the primary problem that needs fixing, although it is part
of it. The problem is that the host can provide a throttling error and
the guest will need to continue trying the exact same request or else
end up locking themself out of the vmpck due to the IV reuse patch
Peter sent.

I think Sean's request to keep throttling a host problem in user space
is not the right one in this case. That would avoid scheduling the
whole vCPU, but the guest code I'm proposing can do other useful work
while waiting. There will be no other code that depends on that
particular control flow.

If we call this one-liner the fix, then the VM guest still has the IV
reuse problem unless it can guarantee that globally no other thread
than the one requesting an attestation report will continue to retry
upon a throttling error in the exitinfo2 value. I wouldn't call that a
fix.

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

Re: [PATCH v12 2/3] x86/sev: Change snp_guest_issue_request's fw_err

[Borislav Petkov]

On Mon, Jan 23, 2023 at 01:22:07PM -0800, Dionna Amalie Glaze wrote:
> This isn't the primary problem that needs fixing, although it is part
> of it.

I'm replying to the 2/3 patch which is addressing this part.

> The problem is that the host can provide a throttling error and
> the guest will need to continue trying the exact same request or else
> end up locking themself out of the vmpck due to the IV reuse patch
> Peter sent.
> 
> I think Sean's request to keep throttling a host problem in user space

+ Sean.

> is not the right one in this case. That would avoid scheduling the
> whole vCPU, but the guest code I'm proposing can do other useful work
> while waiting. There will be no other code that depends on that
> particular control flow.

I know there's another issue but my angle is this:

You have a patch with Fixes tags and they all are fixing some shortcomings. Now,
those are good candidates for stable.

In order to be backportable to stable, those fixes should be as minimal as
possible so that a stable backport does not turn into a nightmare. By the looks
of it, your patches could be simplified to the bare minimum fixes. Cleanups and
improvements can go ontop.

That is, provided we want them in stable and by the looks of it, we probably do.

Which then means, you could do the minimal fixes first and then the cleanups
ontop.

Then, please try to structure your commit messages in a format close to:

Problem is A.

It happens because of B.

Fix it by doing C.

(Potentially do D).

I'm having hard time parsing

https://lore.kernel.org/all/20230120214857.835931-4-dionnaglaze@google.com/

Only in the second paragraph it is talking about what the problem is. And by the
looks of it, if the host throttles, then the guest should not return from that
request.

And adding module params for this are most of the time the wrong solution
because then people would have to *know* how to use them.

And before we add module params, the kernel should try to solve this without any
user interaction, if possible.

But I'm not 100% clear on what exactly we're fixing here so let's start first,
please, with a proper description of what the exact issue is and how it happens.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v12 2/3] x86/sev: Change snp_guest_issue_request's fw_err

[Sean Christopherson]

On Tue, Jan 24, 2023, Borislav Petkov wrote:
> On Mon, Jan 23, 2023 at 01:22:07PM -0800, Dionna Amalie Glaze wrote:
> > This isn't the primary problem that needs fixing, although it is part
> > of it.
> 
> I'm replying to the 2/3 patch which is addressing this part.
> 
> > The problem is that the host can provide a throttling error and
> > the guest will need to continue trying the exact same request or else
> > end up locking themself out of the vmpck due to the IV reuse patch
> > Peter sent.
> > 
> > I think Sean's request to keep throttling a host problem in user space
> 
> + Sean.

It was not a request, it was a question[*].  In the same paragraph I even asked
if the guest was expected to schedule out the blocked task.

 : Why does throttling just punt back to the guest?  E.g. why not exit to userspace
 : and let userspace stall the vCPU?  Is the guest expected to schedule out the task
 : that's trying to make the request?

[*] https://lore.kernel.org/all/Y8rEFpbMV58yJIKy@google.com

> > is not the right one in this case. That would avoid scheduling the
> > whole vCPU, but the guest code I'm proposing can do other useful work
> > while waiting. There will be no other code that depends on that
> > particular control flow.

Relying on host behavior for this sort of thing is also a bad idea.   There is no
contract between the guest and host beyond the host being able to say "you've been
throttled".

Similar to Boris's comments about splitting this patch to fix bugs, separate the
handling of SNP_GUEST_VMM_ERR_BUSY from the internal ratelimiting.  For all intents
and purpsoses, gracefully handling SNP_GUEST_VMM_ERR_BUSY is mandatory.  Ratelimiting
requests from the guest side is a completely different story.

[PATCH v12 3/3] virt: sev-guest: interpret VMM errors from guest request

[Dionna Glaze]

The GHCB specification states that the upper 32 bits of exitinfo2 are
for the VMM's error codes. The sev-guest ABI has already locked in
that the fw_err status of the input will be 64 bits, and that
BIT_ULL(32) means that the extended guest request's data buffer was too
small. Add BIT_ULL(33) for "host refused the request for throttling
reasons".

The driver interprets the upper 32 bits of exitinfo2 for the user
anyway in case the request gets throttled. For safety, since the
encryption algorithm in GHCBv2 is AES_GCM, control must remain in the
kernel to complete the request with the current sequence number.
Returning without finishing the request allows the the guest to make
another request but with different message contents. This is IV reuse,
and breaks cryptographic protections.

When throttled, the driver will reschedule itself and then try
again after sleeping half its ratelimit time to avoid a big wait queue.
The ioctl may block indefinitely, but that has always been the case
when deferring these requests to the host.

Cc: Tom Lendacky <Thomas.Lendacky@amd.com>
Cc: Peter Gonda <pgonda@google.com>
Cc: Borislav Petkov <Borislav.Petkov@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Liam Merwick <liam.merwick@oracle.com>
Cc: Yang Yingliang <yangyingliang@huawei.com>
Cc: Haowen Bai <baihaowen@meizu.com>

Reviewed-by: Tom Lendacky <Thomas.Lendacky@amd.com>
Reviewed-by: Peter Gonda <pgonda@google.com>
Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
---
 Documentation/virt/coco/sev-guest.rst   | 21 +++++++++++------
 drivers/virt/coco/sev-guest/sev-guest.c | 31 +++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/Documentation/virt/coco/sev-guest.rst b/Documentation/virt/coco/sev-guest.rst
index e76393e389eb..fd8bf833f1cd 100644
--- a/Documentation/virt/coco/sev-guest.rst
+++ b/Documentation/virt/coco/sev-guest.rst
@@ -37,11 +37,12 @@ along with a description:
       the return value.  General error numbers (-ENOMEM, -EINVAL)
       are not detailed, but errors with specific meanings are.
 
-The guest ioctl should be issued on a file descriptor of the /dev/sev-guest device.
-The ioctl accepts struct snp_user_guest_request. The input and output structure is
-specified through the req_data and resp_data field respectively. If the ioctl fails
-to execute due to a firmware error, then fw_err code will be set otherwise the
-fw_err will be set to 0x00000000ffffffff, i.e., the lower 32-bits are -1.
+The guest ioctl should be issued on a file descriptor of the
+/dev/sev-guest device.  The ioctl accepts struct
+snp_user_guest_request. The input and output structure is specified
+through the req_data and resp_data field respectively. If the ioctl
+fails to execute due to a firmware error, then the fw_error code will
+be set, otherwise fw_error will be set to -1.
 
 The firmware checks that the message sequence counter is one greater than
 the guests message sequence counter. If guest driver fails to increment message
@@ -57,8 +58,14 @@ counter (e.g. counter overflow), then -EIO will be returned.
                 __u64 req_data;
                 __u64 resp_data;
 
-                /* firmware error code on failure (see psp-sev.h) */
-                __u64 fw_err;
+		/* bits[63:32]: VMM error code, bits[31:0] firmware error code (see psp-sev.h) */
+		union {
+			__u64 exitinfo2;
+			struct {
+				__u32 fw_error;
+		                __u32 vmm_error;
+			};
+		};
         };
 
 2.1 SNP_GET_REPORT
diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index ed6fc14f6b00..1bffd9b1b7dc 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -14,6 +14,7 @@
 #include <linux/io.h>
 #include <linux/platform_device.h>
 #include <linux/miscdevice.h>
+#include <linux/ratelimit.h>
 #include <linux/set_memory.h>
 #include <linux/fs.h>
 #include <crypto/aead.h>
@@ -48,12 +49,22 @@ struct snp_guest_dev {
 	struct snp_req_data input;
 	u32 *os_area_msg_seqno;
 	u8 *vmpck;
+
+	struct ratelimit_state rs;
 };
 
 static u32 vmpck_id;
 module_param(vmpck_id, uint, 0444);
 MODULE_PARM_DESC(vmpck_id, "The VMPCK ID to use when communicating with the PSP.");
 
+static int rate_s = 1;
+module_param(rate_s, int, 0444);
+MODULE_PARM_DESC(rate_s, "The rate limit interval in seconds to limit requests to.");
+
+static int rate_burst = 2;
+module_param(rate_burst, int, 0444);
+MODULE_PARM_DESC(rate_burst, "The rate limit burst amount to limit requests to.");
+
 /* Mutex to serialize the shared buffer access and command handling. */
 static DEFINE_MUTEX(snp_cmd_mutex);
 
@@ -338,6 +349,16 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
 	if (rc)
 		return rc;
 
+retry:
+	/*
+	 * Rate limit commands internally since the host can also throttle, and
+	 * the guest shouldn't create a tight request spin that could end up
+	 * getting this VM throttled more heavily.
+	 */
+	if (!__ratelimit(&snp_dev->rs)) {
+		schedule_timeout_interruptible((rate_s * HZ) / 2);
+		goto retry;
+	}
 	/*
 	 * Call firmware to process the request. In this function the encrypted
 	 * message enters shared memory with the host. So after this call the
@@ -347,6 +368,14 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
 	rc = snp_issue_guest_request(exit_code, &snp_dev->input,
 				     &arg->exitinfo2);
 
+	/*
+	 * The host may return EBUSY if the request has been throttled.
+	 * We retry in the driver to avoid returning and reusing the message
+	 * sequence number on a different message.
+	 */
+	if (arg->vmm_error == SNP_GUEST_VMM_ERR_BUSY)
+		goto retry;
+
 	/*
 	 * If the extended guest request fails due to having too small of a
 	 * certificate data buffer, retry the same guest request without the
@@ -751,6 +780,8 @@ static int __init sev_guest_probe(struct platform_device *pdev)
 	if (ret)
 		goto e_free_cert_data;
 
+	ratelimit_state_init(&snp_dev->rs, rate_s * HZ, rate_burst);
+
 	dev_info(dev, "Initialized SEV guest driver (using vmpck_id %d)\n", vmpck_id);
 	return 0;
 
-- 
2.39.0.246.g2a6d74b583-goog