[PATCH 00/11] SEV: Cleanup sev-guest a bit and add throttling

[PATCH 00/11] SEV: Cleanup sev-guest a bit and add throttling

[Borislav Petkov]

From: "Borislav Petkov (AMD)" <bp@alien8.de>

Hi,

so I've been looking at Dionna's patches adding the SEV guest throttling
and that request issuing spaghetti was getting on my nerves. And it
would've become even worse with more stuff piling ontop so here's
a first round of cleanups before adding more stuff and making it an
unmaintainable mess.

The final result is a lot easier to read with proper separation of
functionality between functions. I want to get rid of more input/output
params being passed back'n'forth and use a struct instead and Nikunj's
patches have stuff which goes in that direction but first things first.

After the cleanup, the new stuff being added is a lot less code and
almost trivial. But I've been staring at this for a while now so it
could be only me who thinks it is trivial now. But we'll see.

Initial smoke testing seems to work ok but I might've introduced some
funky bugs, ofc.

Comments and suggestions are appreciated, as always.

Thanks and thanks, Tom, for the help!

Borislav Petkov (AMD) (7):
  virt/coco/sev-guest: Check SEV_SNP attribute at probe time
  virt/coco/sev-guest: Simplify extended guest request handling
  virt/coco/sev-guest: Remove the disable_vmpck label in
    handle_guest_request()
  virt/coco/sev-guest: Carve out the request issuing logic into a helper
  virt/coco/sev-guest: Do some code style cleanups
  virt/coco/sev-guest: Convert the sw_exit_info_2 checking to a
    switch-case
  crypto: ccp: Get rid of __sev_platform_init_locked()'s local function
    pointer

Dionna Glaze (3):
  virt/coco/sev-guest: Add throttling awareness
  virt/coco/sev-guest: Double-buffer messages
  x86/sev: Change snp_guest_issue_request()'s fw_err argument

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

 Documentation/virt/coco/sev-guest.rst   |  20 ++-
 arch/x86/include/asm/sev-common.h       |   3 -
 arch/x86/include/asm/sev.h              |   4 +-
 arch/x86/kernel/sev.c                   |  33 +++--
 drivers/crypto/ccp/sev-dev.c            |  22 +--
 drivers/virt/coco/sev-guest/sev-guest.c | 169 +++++++++++++++---------
 include/uapi/linux/psp-sev.h            |   7 +
 include/uapi/linux/sev-guest.h          |  18 ++-
 8 files changed, 181 insertions(+), 95 deletions(-)

-- 
2.35.1

[PATCH 01/11] crypto: ccp - Name -1 return value as SEV_RET_NO_FW_CALL

[Borislav Petkov]

From: Peter Gonda <pgonda@google.com>

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

  [ bp: Massage a bit. ]

Signed-off-by: Peter Gonda <pgonda@google.com>
Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/20221207010210.2563293-2-dionnaglaze@google.com
---
 Documentation/virt/coco/sev-guest.rst | 4 ++--
 drivers/crypto/ccp/sev-dev.c          | 8 +++++---
 include/uapi/linux/psp-sev.h          | 7 +++++++
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/Documentation/virt/coco/sev-guest.rst b/Documentation/virt/coco/sev-guest.rst
index bf593e88cfd9..aa3e4c6a1f90 100644
--- a/Documentation/virt/coco/sev-guest.rst
+++ b/Documentation/virt/coco/sev-guest.rst
@@ -40,8 +40,8 @@ along with a description:
 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 0x00000000000000ff.
+to execute due to a firmware error, then fw_err code will be set. Otherwise, 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..f60bb73edfda 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -442,10 +442,10 @@ static int __sev_init_ex_locked(int *error)
 
 static int __sev_platform_init_locked(int *error)
 {
+	int rc = 0, psp_ret = SEV_RET_NO_FW_CALL;
 	struct psp_device *psp = psp_master;
-	struct sev_device *sev;
-	int rc = 0, psp_ret = -1;
 	int (*init_function)(int *error);
+	struct sev_device *sev;
 
 	if (!psp || !psp->sev_data)
 		return -ENODEV;
@@ -473,9 +473,11 @@ 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.");
+		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);
 	}
+
 	if (error)
 		*error = psp_ret;
 
diff --git a/include/uapi/linux/psp-sev.h b/include/uapi/linux/psp-sev.h
index 91b4c63d5cbf..1c9da485318f 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. Its purpose is 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,
-- 
2.35.1

[PATCH 02/11] virt/coco/sev-guest: Check SEV_SNP attribute at probe time

[Borislav Petkov]

From: "Borislav Petkov (AMD)" <bp@alien8.de>

No need to check it on every ioctl. And yes, this is a common SEV driver
but it does only SNP-specific operations currently. This can be
revisited later, when more use cases appear.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 arch/x86/kernel/sev.c                   | 3 ---
 drivers/virt/coco/sev-guest/sev-guest.c | 3 +++
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 679026a640ef..c644c34372e8 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2183,9 +2183,6 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned
 	struct ghcb *ghcb;
 	int ret;
 
-	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
-		return -ENODEV;
-
 	if (!fw_err)
 		return -EINVAL;
 
diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index 4ec4174e05a3..edaf6031c6d9 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -689,6 +689,9 @@ static int __init sev_guest_probe(struct platform_device *pdev)
 	void __iomem *mapping;
 	int ret;
 
+	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+		return -ENODEV;
+
 	if (!dev->platform_data)
 		return -ENODEV;
 
-- 
2.35.1

[PATCH 03/11] virt/coco/sev-guest: Simplify extended guest request handling

[Borislav Petkov]

From: "Borislav Petkov (AMD)" <bp@alien8.de>

Return a specific error code - -ENOSPC - to signal the too small cert
data buffer instead of checking exit code and exitinfo2.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 arch/x86/kernel/sev.c                   |  8 +++--
 drivers/virt/coco/sev-guest/sev-guest.c | 46 ++++++++++++++-----------
 2 files changed, 30 insertions(+), 24 deletions(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index c644c34372e8..ee53cab887fa 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2212,12 +2212,14 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned
 	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_REQ_INVALID_LEN) {
 			input->data_npages = ghcb_get_rbx(ghcb);
+			ret = -ENOSPC;
+		} else {
+			ret = -EIO;
+		}
 
 		*fw_err = ghcb->save.sw_exit_info_2;
-
-		ret = -EIO;
 	}
 
 e_put:
diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index edaf6031c6d9..5b4cddf44a3a 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -322,7 +322,8 @@ 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, override_err = 0;
+	unsigned int override_npages = 0;
 	u64 seqno;
 	int rc;
 
@@ -338,6 +339,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 	if (rc)
 		return rc;
 
+retry_request:
 	/*
 	 * Call firmware to process the request. In this function the encrypted
 	 * message enters shared memory with the host. So after this call the
@@ -346,17 +348,24 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 	 */
 	rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
 
-	/*
-	 * If the extended guest request fails due to having too small of a
-	 * certificate data buffer, retry the same guest request without the
-	 * extended data request in order to increment the sequence number
-	 * and thus avoid IV reuse.
-	 */
-	if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST &&
-	    err == SNP_GUEST_REQ_INVALID_LEN) {
-		const unsigned int certs_npages = snp_dev->input.data_npages;
+	switch (rc) {
+	case -ENOSPC:
+		/*
+		 * If the extended guest request fails due to having too
+		 * small of a certificate data buffer, retry the same
+		 * guest request without the extended data request in
+		 * order to increment the sequence number and thus avoid
+		 * IV reuse.
+		 */
+		override_npages = snp_dev->input.data_npages;
+		exit_code	= SVM_VMGEXIT_GUEST_REQUEST;
 
-		exit_code = SVM_VMGEXIT_GUEST_REQUEST;
+		/*
+		 * Override the error to inform callers the given extended
+		 * request buffer size was too small and give the caller the
+		 * required buffer size.
+		 */
+		override_err	= SNP_GUEST_REQ_INVALID_LEN;
 
 		/*
 		 * If this call to the firmware succeeds, the sequence number can
@@ -366,19 +375,14 @@ 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);
-
-		/*
-		 * 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;
-		snp_dev->input.data_npages = certs_npages;
+		goto retry_request;
 	}
 
 	if (fw_err)
-		*fw_err = err;
+		*fw_err = override_err ?: err;
+
+	if (override_npages)
+		snp_dev->input.data_npages = override_npages;
 
 	if (rc) {
 		dev_alert(snp_dev->dev,
-- 
2.35.1

[PATCH 04/11] virt/coco/sev-guest: Remove the disable_vmpck label in handle_guest_request()

[Borislav Petkov]

From: "Borislav Petkov (AMD)" <bp@alien8.de>

Call the function directly instead.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 drivers/virt/coco/sev-guest/sev-guest.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index 5b4cddf44a3a..c0ecc5885573 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -388,7 +388,8 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 		dev_alert(snp_dev->dev,
 			  "Detected error from ASP request. rc: %d, fw_err: %llu\n",
 			  rc, *fw_err);
-		goto disable_vmpck;
+		snp_disable_vmpck(snp_dev);
+		return rc;
 	}
 
 	rc = verify_and_dec_payload(snp_dev, resp_buf, resp_sz);
@@ -396,17 +397,14 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 		dev_alert(snp_dev->dev,
 			  "Detected unexpected decode failure from ASP. rc: %d\n",
 			  rc);
-		goto disable_vmpck;
+		snp_disable_vmpck(snp_dev);
+		return rc;
 	}
 
 	/* Increment to new message sequence after payload decryption was successful. */
 	snp_inc_msg_seqno(snp_dev);
 
 	return 0;
-
-disable_vmpck:
-	snp_disable_vmpck(snp_dev);
-	return rc;
 }
 
 static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
-- 
2.35.1

[PATCH 05/11] virt/coco/sev-guest: Carve out the request issuing logic into a helper

[Borislav Petkov]

From: "Borislav Petkov (AMD)" <bp@alien8.de>

This makes the code flow a lot easier to follow.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 drivers/virt/coco/sev-guest/sev-guest.c | 41 +++++++++++++++----------
 1 file changed, 24 insertions(+), 17 deletions(-)

diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index c0ecc5885573..e72289de2b28 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -318,27 +318,12 @@ 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, __u64 *fw_err)
 {
 	unsigned long err, override_err = 0;
 	unsigned int override_npages = 0;
-	u64 seqno;
 	int rc;
 
-	/* Get message sequence and verify that its a non-zero */
-	seqno = snp_get_msg_seqno(snp_dev);
-	if (!seqno)
-		return -EIO;
-
-	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);
-	if (rc)
-		return rc;
-
 retry_request:
 	/*
 	 * Call firmware to process the request. In this function the encrypted
@@ -347,7 +332,6 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 	 * prevent reuse of the IV.
 	 */
 	rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
-
 	switch (rc) {
 	case -ENOSPC:
 		/*
@@ -384,6 +368,29 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 	if (override_npages)
 		snp_dev->input.data_npages = override_npages;
 
+	return rc;
+}
+
+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)
+{
+	u64 seqno;
+	int rc;
+
+	/* Get message sequence and verify that its a non-zero */
+	seqno = snp_get_msg_seqno(snp_dev);
+	if (!seqno)
+		return -EIO;
+
+	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);
+	if (rc)
+		return rc;
+
+	rc = __handle_guest_request(snp_dev, exit_code, fw_err);
 	if (rc) {
 		dev_alert(snp_dev->dev,
 			  "Detected error from ASP request. rc: %d, fw_err: %llu\n",
-- 
2.35.1

[PATCH 06/11] virt/coco/sev-guest: Do some code style cleanups

[Borislav Petkov]

From: "Borislav Petkov (AMD)" <bp@alien8.de>

Remove unnecessary linebreaks, make the code more compact.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 drivers/virt/coco/sev-guest/sev-guest.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index e72289de2b28..d430e2be2a22 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -392,18 +392,14 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 
 	rc = __handle_guest_request(snp_dev, exit_code, fw_err);
 	if (rc) {
-		dev_alert(snp_dev->dev,
-			  "Detected error from ASP request. rc: %d, fw_err: %llu\n",
-			  rc, *fw_err);
+		dev_alert(snp_dev->dev, "Detected error from ASP request. rc: %d, fw_err: %llu\n", rc, *fw_err);
 		snp_disable_vmpck(snp_dev);
 		return rc;
 	}
 
 	rc = verify_and_dec_payload(snp_dev, resp_buf, resp_sz);
 	if (rc) {
-		dev_alert(snp_dev->dev,
-			  "Detected unexpected decode failure from ASP. rc: %d\n",
-			  rc);
+		dev_alert(snp_dev->dev, "Detected unexpected decode failure from ASP. rc: %d\n", rc);
 		snp_disable_vmpck(snp_dev);
 		return rc;
 	}
-- 
2.35.1

[PATCH 07/11] virt/coco/sev-guest: Convert the sw_exit_info_2 checking to a switch-case

[Borislav Petkov]

From: "Borislav Petkov (AMD)" <bp@alien8.de>

snp_issue_guest_request() checks the value returned by the hypervisor in
sw_exit_info_2 and returns a different error depending on it.

Convert those checks into a switch-case to make it more readable when
more error values are going to be checked in the future.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 arch/x86/kernel/sev.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index ee53cab887fa..d6655fccefc8 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2209,17 +2209,23 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned
 	if (ret)
 		goto e_put;
 
-	if (ghcb->save.sw_exit_info_2) {
+	*fw_err = ghcb->save.sw_exit_info_2;
+	switch (*fw_err) {
+	case 0:
+		break;
+
+	case SNP_GUEST_REQ_INVALID_LEN:
 		/* 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) {
+		if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST) {
 			input->data_npages = ghcb_get_rbx(ghcb);
 			ret = -ENOSPC;
-		} else {
-			ret = -EIO;
+			break;
 		}
+		fallthrough;
 
-		*fw_err = ghcb->save.sw_exit_info_2;
+	default:
+		ret = -EIO;
+		break;
 	}
 
 e_put:
-- 
2.35.1

[PATCH 08/11] virt/coco/sev-guest: Add throttling awareness

[Borislav Petkov]

From: Dionna Glaze <dionnaglaze@google.com>

A potentially malicious SEV guest can constantly hammer the hypervisor
using this driver to send down requests and thus prevent or at least
considerably hinder other guests from issuing requests to the secure
processor which is a shared platform resource.

Therefore, the host is permitted and encouraged to throttle such guest
requests.

Add the capability to handle the case when the hypervisor throttles
excessive numbers of requests issued by the guest. Otherwise, the VM
platform communication key will be disabled, preventing the guest from
attesting itself.

Realistically speaking, a well-behaved guest should not even care about
throttling. During its lifetime, it would end up issuing a handful of
requests which the hardware can easily handle.

This is more to address the case of a malicious guest. Such guest should
get throttled and if its VMPCK gets disabled, then that's its own
wrongdoing and perhaps that guest even deserves it.

To the implementation: the hypervisor signals with SNP_GUEST_REQ_ERR_BUSY
that the guest requests should be throttled. That error code is returned
in the upper 32-bit half of exitinfo2 and this is part of the GHCB spec
v2.

So the guest is given a throttling period of 1 minute in which it
retries the request every 2 seconds. This is a good default but if it
turns out to not pan out in practice, it can be tweaked later.

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
guest to make another request but with different message contents. This
is IV reuse, and breaks cryptographic protections.

  [ bp: Rewrite commit message and do a simplified version. ]

Fixes: d5af44dde546 ("x86/sev: Provide support for SNP guest request NAEs")
Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
Co-developed-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230214164638.1189804-2-dionnaglaze@google.com
---
 arch/x86/include/asm/sev-common.h       |  3 ++-
 arch/x86/kernel/sev.c                   |  4 ++++
 drivers/virt/coco/sev-guest/sev-guest.c | 19 ++++++++++++++++++-
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index b8357d6ecd47..b63be696b776 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -128,8 +128,9 @@ struct snp_psc_desc {
 	struct psc_entry entries[VMGEXIT_PSC_MAX_ENTRY];
 } __packed;
 
-/* Guest message request error code */
+/* Guest message request error codes */
 #define SNP_GUEST_REQ_INVALID_LEN	BIT_ULL(32)
+#define SNP_GUEST_REQ_ERR_BUSY		BIT_ULL(33)
 
 #define GHCB_MSR_TERM_REQ		0x100
 #define GHCB_MSR_TERM_REASON_SET_POS	12
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index d6655fccefc8..612453eb7ab3 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2214,6 +2214,10 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned
 	case 0:
 		break;
 
+	case SNP_GUEST_REQ_ERR_BUSY:
+		ret = -EAGAIN;
+		break;
+
 	case SNP_GUEST_REQ_INVALID_LEN:
 		/* Number of expected pages are returned in RBX */
 		if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST) {
diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index d430e2be2a22..ca501d119233 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -31,6 +31,9 @@
 #define AAD_LEN		48
 #define MSG_HDR_VER	1
 
+#define SNP_REQ_MAX_RETRY_DURATION	(60*HZ)
+#define SNP_REQ_RETRY_DELAY		(2*HZ)
+
 struct snp_guest_crypto {
 	struct crypto_aead *tfm;
 	u8 *iv, *authtag;
@@ -320,8 +323,9 @@ static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8
 
 static int __handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, __u64 *fw_err)
 {
-	unsigned long err, override_err = 0;
+	unsigned long err = 0xff, override_err = 0;
 	unsigned int override_npages = 0;
+	unsigned long req_start = jiffies;
 	int rc;
 
 retry_request:
@@ -360,6 +364,19 @@ static int __handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
 		 * user as an ioctl() return code.
 		 */
 		goto retry_request;
+
+	/*
+	 * The host may return SNP_GUEST_REQ_ERR_EBUSY if the request has been
+	 * throttled. Retry in the driver to avoid returning and reusing the
+	 * message sequence number on a different message.
+	 */
+	case -EAGAIN:
+		if (jiffies - req_start > SNP_REQ_MAX_RETRY_DURATION) {
+			rc = -ETIMEDOUT;
+			break;
+		}
+		schedule_timeout_killable(SNP_REQ_RETRY_DELAY);
+		goto retry_request;
 	}
 
 	if (fw_err)
-- 
2.35.1

[PATCH 09/11] virt/coco/sev-guest: Double-buffer messages

[Borislav Petkov]

From: Dionna Glaze <dionnaglaze@google.com>

The encryption algorithms read and write directly to shared unencrypted
memory, which may leak information as well as permit the host to tamper
with the message integrity. Instead, copy whole messages in or out as
needed before doing any computation on them.

Fixes: d5af44dde546 ("x86/sev: Provide support for SNP guest request NAEs")
Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230214164638.1189804-3-dionnaglaze@google.com
---
 drivers/virt/coco/sev-guest/sev-guest.c | 27 +++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index ca501d119233..070c6f414bfd 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -46,7 +46,15 @@ struct snp_guest_dev {
 
 	void *certs_data;
 	struct snp_guest_crypto *crypto;
+	/* request and response are in unencrypted memory */
 	struct snp_guest_msg *request, *response;
+
+	/*
+	 * Avoid information leakage by double-buffering shared messages
+	 * in fields that are in regular encrypted memory.
+	 */
+	struct snp_guest_msg secret_request, secret_response;
+
 	struct snp_secrets_page_layout *layout;
 	struct snp_req_data input;
 	u32 *os_area_msg_seqno;
@@ -266,14 +274,17 @@ static int dec_payload(struct snp_guest_dev *snp_dev, struct snp_guest_msg *msg,
 static int verify_and_dec_payload(struct snp_guest_dev *snp_dev, void *payload, u32 sz)
 {
 	struct snp_guest_crypto *crypto = snp_dev->crypto;
-	struct snp_guest_msg *resp = snp_dev->response;
-	struct snp_guest_msg *req = snp_dev->request;
+	struct snp_guest_msg *resp = &snp_dev->secret_response;
+	struct snp_guest_msg *req = &snp_dev->secret_request;
 	struct snp_guest_msg_hdr *req_hdr = &req->hdr;
 	struct snp_guest_msg_hdr *resp_hdr = &resp->hdr;
 
 	dev_dbg(snp_dev->dev, "response [seqno %lld type %d version %d sz %d]\n",
 		resp_hdr->msg_seqno, resp_hdr->msg_type, resp_hdr->msg_version, resp_hdr->msg_sz);
 
+	/* Copy response from shared memory to encrypted memory. */
+	memcpy(resp, snp_dev->response, sizeof(*resp));
+
 	/* Verify that the sequence counter is incremented by 1 */
 	if (unlikely(resp_hdr->msg_seqno != (req_hdr->msg_seqno + 1)))
 		return -EBADMSG;
@@ -297,7 +308,7 @@ static int verify_and_dec_payload(struct snp_guest_dev *snp_dev, void *payload,
 static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8 type,
 			void *payload, size_t sz)
 {
-	struct snp_guest_msg *req = snp_dev->request;
+	struct snp_guest_msg *req = &snp_dev->secret_request;
 	struct snp_guest_msg_hdr *hdr = &req->hdr;
 
 	memset(req, 0, sizeof(*req));
@@ -400,13 +411,21 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 	if (!seqno)
 		return -EIO;
 
+	/* Clear shared memory's response for the host to populate. */
 	memset(snp_dev->response, 0, sizeof(struct snp_guest_msg));
 
-	/* Encrypt the userspace provided payload */
+	/* Encrypt the userspace provided payload in snp_dev->secret_request. */
 	rc = enc_payload(snp_dev, seqno, msg_ver, type, req_buf, req_sz);
 	if (rc)
 		return rc;
 
+	/*
+	 * Write the fully encrypted request to the shared unencrypted
+	 * request page.
+	 */
+	memcpy(snp_dev->request, &snp_dev->secret_request,
+	       sizeof(snp_dev->secret_request));
+
 	rc = __handle_guest_request(snp_dev, exit_code, fw_err);
 	if (rc) {
 		dev_alert(snp_dev->dev, "Detected error from ASP request. rc: %d, fw_err: %llu\n", rc, *fw_err);
-- 
2.35.1

[PATCH 10/11] crypto: ccp: Get rid of __sev_platform_init_locked()'s local function pointer

[Borislav Petkov]

From: "Borislav Petkov (AMD)" <bp@alien8.de>

Add a wrapper instead.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 drivers/crypto/ccp/sev-dev.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index f60bb73edfda..c54cc8f9a284 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -440,11 +440,18 @@ 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)
 {
 	int rc = 0, psp_ret = SEV_RET_NO_FW_CALL;
 	struct psp_device *psp = psp_master;
-	int (*init_function)(int *error);
 	struct sev_device *sev;
 
 	if (!psp || !psp->sev_data)
@@ -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
@@ -475,7 +479,7 @@ static int __sev_platform_init_locked(int *error)
 		 */
 		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);
+		rc = __sev_do_init_locked(&psp_ret);
 	}
 
 	if (error)
-- 
2.35.1

[PATCH 11/11] x86/sev: Change snp_guest_issue_request()'s fw_err argument

[Borislav Petkov]

From: Dionna Glaze <dionnaglaze@google.com>

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 to
snp_guest_issue_request() 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*. Change this
type for issuing the guest request. Pass the ioctl command struct's error
field directly instead of in 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 bookend the call with the no
firmware call error and clear the error.

Since the "fw_err" field is really exitinfo2 split into the upper bits'
vmm error code and lower bits' firmware error code, convert the 64 bit
value to a union.

  [ bp: Massage commit message, adjust code. ]

Signed-off-by: Dionna Glaze <dionnaglaze@google.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230214164638.1189804-5-dionnaglaze@google.com
---
 Documentation/virt/coco/sev-guest.rst   | 20 ++++++----
 arch/x86/include/asm/sev-common.h       |  4 --
 arch/x86/include/asm/sev.h              |  4 +-
 arch/x86/kernel/sev.c                   | 16 +++++---
 drivers/virt/coco/sev-guest/sev-guest.c | 51 ++++++++++++-------------
 include/uapi/linux/sev-guest.h          | 18 ++++++++-
 6 files changed, 66 insertions(+), 47 deletions(-)

diff --git a/Documentation/virt/coco/sev-guest.rst b/Documentation/virt/coco/sev-guest.rst
index aa3e4c6a1f90..68b0d2363af8 100644
--- a/Documentation/virt/coco/sev-guest.rst
+++ b/Documentation/virt/coco/sev-guest.rst
@@ -37,11 +37,11 @@ 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, 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 +57,14 @@ 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/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index b63be696b776..0759af9b1acf 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -128,10 +128,6 @@ struct snp_psc_desc {
 	struct psc_entry entries[VMGEXIT_PSC_MAX_ENTRY];
 } __packed;
 
-/* Guest message request error codes */
-#define SNP_GUEST_REQ_INVALID_LEN	BIT_ULL(32)
-#define SNP_GUEST_REQ_ERR_BUSY		BIT_ULL(33)
-
 #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 612453eb7ab3..1035d3eed77e 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;
@@ -2183,9 +2185,11 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned
 	struct ghcb *ghcb;
 	int ret;
 
-	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.
@@ -2209,16 +2213,16 @@ int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned
 	if (ret)
 		goto e_put;
 
-	*fw_err = ghcb->save.sw_exit_info_2;
-	switch (*fw_err) {
+	*exitinfo2 = ghcb->save.sw_exit_info_2;
+	switch (*exitinfo2) {
 	case 0:
 		break;
 
-	case SNP_GUEST_REQ_ERR_BUSY:
+	case SNP_GUEST_VMM_ERR(SNP_GUEST_VMM_ERR_BUSY):
 		ret = -EAGAIN;
 		break;
 
-	case SNP_GUEST_REQ_INVALID_LEN:
+	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);
diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index 070c6f414bfd..a5b68e43fa27 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -332,11 +332,11 @@ 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, __u64 *fw_err)
+static int __handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
+				  struct snp_guest_request_ioctl *req_ioctl)
 {
-	unsigned long err = 0xff, override_err = 0;
-	unsigned int override_npages = 0;
 	unsigned long req_start = jiffies;
+	unsigned int override_npages = 0;
 	int rc;
 
 retry_request:
@@ -346,7 +346,7 @@ 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, &err);
+	rc = snp_issue_guest_request(exit_code, &snp_dev->input, &req_ioctl->exitinfo2);
 	switch (rc) {
 	case -ENOSPC:
 		/*
@@ -357,14 +357,14 @@ static int __handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
 		 * IV reuse.
 		 */
 		override_npages = snp_dev->input.data_npages;
-		exit_code	= SVM_VMGEXIT_GUEST_REQUEST;
+		exit_code = SVM_VMGEXIT_GUEST_REQUEST;
 
 		/*
 		 * Override the error to inform callers the given extended
 		 * request buffer size was too small and give the caller the
 		 * required buffer size.
 		 */
-		override_err	= SNP_GUEST_REQ_INVALID_LEN;
+		req_ioctl->vmm_error = SNP_GUEST_VMM_ERR_INVALID_LEN;
 
 		/*
 		 * If this call to the firmware succeeds, the sequence number can
@@ -377,7 +377,7 @@ static int __handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
 		goto retry_request;
 
 	/*
-	 * The host may return SNP_GUEST_REQ_ERR_EBUSY if the request has been
+	 * The host may return SNP_GUEST_VMM_ERR_BUSY if the request has been
 	 * throttled. Retry in the driver to avoid returning and reusing the
 	 * message sequence number on a different message.
 	 */
@@ -390,18 +390,16 @@ static int __handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
 		goto retry_request;
 	}
 
-	if (fw_err)
-		*fw_err = override_err ?: err;
-
 	if (override_npages)
 		snp_dev->input.data_npages = override_npages;
 
 	return rc;
 }
 
-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 *req_ioctl, u8 type,
+				void *req_buf, size_t req_sz, void *resp_buf,
+				u32 resp_sz)
 {
 	u64 seqno;
 	int rc;
@@ -415,7 +413,7 @@ 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 in snp_dev->secret_request. */
-	rc = enc_payload(snp_dev, seqno, msg_ver, type, req_buf, req_sz);
+	rc = enc_payload(snp_dev, seqno, req_ioctl->msg_version, type, req_buf, req_sz);
 	if (rc)
 		return rc;
 
@@ -426,9 +424,11 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
 	memcpy(snp_dev->request, &snp_dev->secret_request,
 	       sizeof(snp_dev->secret_request));
 
-	rc = __handle_guest_request(snp_dev, exit_code, fw_err);
+	rc = __handle_guest_request(snp_dev, exit_code, req_ioctl);
 	if (rc) {
-		dev_alert(snp_dev->dev, "Detected error from ASP request. rc: %d, fw_err: %llu\n", rc, *fw_err);
+		dev_alert(snp_dev->dev,
+			  "Detected error from ASP request. rc: %d, exitinfo2: %llu\n",
+			  rc, req_ioctl->exitinfo2);
 		snp_disable_vmpck(snp_dev);
 		return rc;
 	}
@@ -471,9 +471,9 @@ 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;
 
@@ -511,9 +511,8 @@ 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;
 
@@ -573,12 +572,12 @@ 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)))
@@ -613,7 +612,7 @@ 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)
@@ -644,7 +643,7 @@ 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_ */
-- 
2.35.1

Re: [PATCH 03/11] virt/coco/sev-guest: Simplify extended guest request handling

[Dionna Amalie Glaze]

>         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_REQ_INVALID_LEN) {
>                         input->data_npages = ghcb_get_rbx(ghcb);
> +                       ret = -ENOSPC;
> +               } else {
> +                       ret = -EIO;
> +               }
>
>                 *fw_err = ghcb->save.sw_exit_info_2;
> -
> -               ret = -EIO;
>         }

I think *fw_err still needs to be hoisted out of this if block so that
a 0 fw_err gets written back to user space rather than the 0xff
placeholder. The 0 would more correctly indicate the lack of an error.


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

Re: [PATCH 11/11] x86/sev: Change snp_guest_issue_request()'s fw_err argument

[Borislav Petkov]

On Thu, Feb 16, 2023 at 01:46:02PM +0100, Borislav Petkov wrote:
> @@ -390,18 +390,16 @@ static int __handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code,
>  		goto retry_request;
>  	}
>  
> -	if (fw_err)
> -		*fw_err = override_err ?: err;
> -

As Tom pointed out offlist, we still need to do the error override.
Frankly, I'm not crazy about this request retrying as we do it but
I guess it is what it is and it is too late to change that now.

-- 
Regards/Gruss,
    Boris.

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