linux/drivers/virt/coco, branch v6.4

x86/sev: Change snp_guest_issue_request()'s fw_err argument

2023-03-21T14:43:19Z

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 - Fix a build issue as Reported-by: kernel test robot Link: https://lore.kernel.org/oe-kbuild-all/202303070609.vX6wp2Af-lkp@intel.com - print exitinfo2 in hex Tom: - Correct -EIO exit case. ] Signed-off-by: Dionna Glaze Signed-off-by: Tom Lendacky Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20230214164638.1189804-5-dionnaglaze@google.com Link: https://lore.kernel.org/r/20230307192449.24732-12-bp@alien8.de

virt/coco/sev-guest: Double-buffer messages

2023-03-21T12:20:04Z

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 Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20230214164638.1189804-3-dionnaglaze@google.com

virt/coco/sev-guest: Add throttling awareness

2023-03-13T12:29:27Z

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

virt/coco/sev-guest: Do some code style cleanups

2023-03-13T11:47:55Z

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

virt/coco/sev-guest: Carve out the request issuing logic into a helper

2023-03-13T11:35:02Z

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

virt/coco/sev-guest: Remove the disable_vmpck label in handle_guest_request()

2023-03-13T10:33:41Z

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

virt/coco/sev-guest: Simplify extended guest request handling

2023-03-13T10:27:10Z

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

virt/coco/sev-guest: Check SEV_SNP attribute at probe time

2023-03-13T10:20:20Z

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

virt/sev-guest: Return -EIO if certificate buffer is not large enough

2023-03-01T09:17:46Z

Commit 47894e0fa6a5 ("virt/sev-guest: Prevent IV reuse in the SNP guest driver") changed the behavior associated with the return value when the caller does not supply a large enough certificate buffer. Prior to the commit a value of -EIO was returned. Now, 0 is returned. This breaks the established ABI with the user. Change the code to detect the buffer size error and return -EIO. Fixes: 47894e0fa6a5 ("virt/sev-guest: Prevent IV reuse in the SNP guest driver") Reported-by: Larry Dewey Signed-off-by: Tom Lendacky Signed-off-by: Borislav Petkov (AMD) Tested-by: Larry Dewey Cc: Link: https://lore.kernel.org/r/2afbcae6daf13f7ad5a4296692e0a0fe1bc1e4ee.1677083979.git.thomas.lendacky@amd.com

Merge tag 'x86_sev_for_v6.2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2022-12-13T23:17:55Z

Pull x86 sev updates from Borislav Petkov: - Two minor fixes to the sev-guest driver * tag 'x86_sev_for_v6.2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: virt/sev-guest: Add a MODULE_ALIAS virt/sev-guest: Remove unnecessary free in init_crypto()