From d6fd48eff7506bb866a54e40369df8899f2078a9 Mon Sep 17 00:00:00 2001 From: "Borislav Petkov (AMD)" Date: Wed, 15 Feb 2023 11:01:42 +0100 Subject: virt/coco/sev-guest: Check SEV_SNP attribute at probe time 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) Reviewed-by: Tom Lendacky Link: https://lore.kernel.org/r/20230307192449.24732-3-bp@alien8.de --- drivers/virt/coco/sev-guest/sev-guest.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'drivers') diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c index 7b4e9009f335..ed5d6ae1a144 100644 --- a/drivers/virt/coco/sev-guest/sev-guest.c +++ b/drivers/virt/coco/sev-guest/sev-guest.c @@ -703,6 +703,9 @@ 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; -- cgit v1.2.3 From 970ab823743fb54b42002ec76c51481f67436444 Mon Sep 17 00:00:00 2001 From: "Borislav Petkov (AMD)" Date: Wed, 15 Feb 2023 11:39:41 +0100 Subject: virt/coco/sev-guest: Simplify extended guest request handling Return a specific error code - -ENOSPC - to signal the too small cert data buffer instead of checking exit code and exitinfo2. While at it, hoist the *fw_err assignment in snp_issue_guest_request() so that a proper error value is returned to the callers. [ Tom: check override_err instead of err. ] Signed-off-by: Borislav Petkov (AMD) Signed-off-by: Tom Lendacky Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20230307192449.24732-4-bp@alien8.de --- arch/x86/kernel/sev.c | 11 ++++---- drivers/virt/coco/sev-guest/sev-guest.c | 48 ++++++++++++++++++--------------- 2 files changed, 32 insertions(+), 27 deletions(-) (limited to 'drivers') diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c index c644c34372e8..6a3e1425ba17 100644 --- a/arch/x86/kernel/sev.c +++ b/arch/x86/kernel/sev.c @@ -2209,15 +2209,16 @@ 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; 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); - - *fw_err = ghcb->save.sw_exit_info_2; - - ret = -EIO; + ret = -ENOSPC; + } else { + 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 ed5d6ae1a144..e61db0b15b7a 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 @@ -366,15 +375,7 @@ 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; } /* @@ -386,7 +387,10 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in snp_inc_msg_seqno(snp_dev); if (fw_err) - *fw_err = err; + *fw_err = override_err ?: err; + + if (override_npages) + snp_dev->input.data_npages = override_npages; /* * If an extended guest request was issued and the supplied certificate @@ -394,7 +398,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in * prevent IV reuse. If the standard request was successful, return -EIO * back to the caller as would have originally been returned. */ - if (!rc && err == SNP_GUEST_REQ_INVALID_LEN) + if (!rc && override_err == SNP_GUEST_REQ_INVALID_LEN) return -EIO; if (rc) { -- cgit v1.2.3 From c5a338274bdb894f088767bea856be344d0ccaef Mon Sep 17 00:00:00 2001 From: "Borislav Petkov (AMD)" Date: Wed, 15 Feb 2023 11:43:43 +0100 Subject: virt/coco/sev-guest: Remove the disable_vmpck label in handle_guest_request() Call the function directly instead. No functional changes. Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Tom Lendacky Link: https://lore.kernel.org/r/20230307192449.24732-5-bp@alien8.de --- drivers/virt/coco/sev-guest/sev-guest.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) (limited to 'drivers') diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c index e61db0b15b7a..a51bd4afd5ab 100644 --- a/drivers/virt/coco/sev-guest/sev-guest.c +++ b/drivers/virt/coco/sev-guest/sev-guest.c @@ -405,7 +405,8 @@ retry_request: 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); @@ -413,14 +414,11 @@ retry_request: 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; } 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) -- cgit v1.2.3 From 0fdb6cc7c89cb5e0cbc45dbdbafb8e3fb92ddc95 Mon Sep 17 00:00:00 2001 From: "Borislav Petkov (AMD)" Date: Tue, 7 Mar 2023 09:19:19 -0600 Subject: virt/coco/sev-guest: Carve out the request issuing logic into a helper This makes the code flow a lot easier to follow. No functional changes. [ Tom: touchups. ] Signed-off-by: Borislav Petkov (AMD) Signed-off-by: Tom Lendacky Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20230307192449.24732-6-bp@alien8.de --- drivers/virt/coco/sev-guest/sev-guest.c | 44 ++++++++++++++++++++------------- 1 file changed, 27 insertions(+), 17 deletions(-) (limited to 'drivers') diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c index a51bd4afd5ab..07dafe22b27a 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 @@ retry_request: * prevent reuse of the IV. */ rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err); - switch (rc) { case -ENOSPC: /* @@ -401,7 +385,33 @@ retry_request: if (!rc && override_err == SNP_GUEST_REQ_INVALID_LEN) return -EIO; + 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) { + if (rc == -EIO && *fw_err == SNP_GUEST_REQ_INVALID_LEN) + return rc; + dev_alert(snp_dev->dev, "Detected error from ASP request. rc: %d, fw_err: %llu\n", rc, *fw_err); -- cgit v1.2.3 From d25bae7dc7b0668cb2a1325c64eb32d5fea4e5a9 Mon Sep 17 00:00:00 2001 From: "Borislav Petkov (AMD)" Date: Wed, 15 Feb 2023 11:54:59 +0100 Subject: virt/coco/sev-guest: Do some code style cleanups Remove unnecessary linebreaks, make the code more compact. No functional changes. Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Tom Lendacky Link: https://lore.kernel.org/r/20230307192449.24732-7-bp@alien8.de --- drivers/virt/coco/sev-guest/sev-guest.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) (limited to 'drivers') diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c index 07dafe22b27a..81a53c31ff46 100644 --- a/drivers/virt/coco/sev-guest/sev-guest.c +++ b/drivers/virt/coco/sev-guest/sev-guest.c @@ -412,18 +412,14 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in if (rc == -EIO && *fw_err == SNP_GUEST_REQ_INVALID_LEN) return 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; } -- cgit v1.2.3 From 72f7754dcf31c87c92c0c353dcf747814cc5ce10 Mon Sep 17 00:00:00 2001 From: Dionna Glaze Date: Thu, 16 Feb 2023 11:08:02 +0100 Subject: virt/coco/sev-guest: Add throttling awareness 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. - The stable tags are supposed to denote that a cleanup should go upfront before backporting this so that any future fixes to this can preserve the sanity of the backporter(s). ] Fixes: d5af44dde546 ("x86/sev: Provide support for SNP guest request NAEs") Signed-off-by: Dionna Glaze Co-developed-by: Borislav Petkov (AMD) Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Tom Lendacky Cc: # d6fd48eff750 ("virt/coco/sev-guest: Check SEV_SNP attribute at probe time") Cc: # 970ab823743f (" virt/coco/sev-guest: Simplify extended guest request handling") Cc: # c5a338274bdb ("virt/coco/sev-guest: Remove the disable_vmpck label in handle_guest_request()") Cc: # 0fdb6cc7c89c ("virt/coco/sev-guest: Carve out the request issuing logic into a helper") Cc: # d25bae7dc7b0 ("virt/coco/sev-guest: Do some code style cleanups") Cc: # fa4ae42cc60a ("virt/coco/sev-guest: Convert the sw_exit_info_2 checking to a switch-case") 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(-) (limited to 'drivers') 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 d67884fb38c1..3f664ab277c4 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 81a53c31ff46..46f1a8d558b0 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; @@ -320,7 +323,8 @@ 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 long req_start = jiffies; unsigned int override_npages = 0; int rc; @@ -360,6 +364,19 @@ retry_request: * 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; } /* -- cgit v1.2.3