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 <lkp@intel.com>
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 <dionnaglaze@google.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230214164638.1189804-5-dionnaglaze@google.com
Link: https://lore.kernel.org/r/20230307192449.24732-12-bp@alien8.de
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: d5af44dde5 ("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
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: d5af44dde5 ("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>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: <stable@kernel.org> # d6fd48eff7 ("virt/coco/sev-guest: Check SEV_SNP attribute at probe time")
Cc: <stable@kernel.org> # 970ab82374 (" virt/coco/sev-guest: Simplify extended guest request handling")
Cc: <stable@kernel.org> # c5a338274b ("virt/coco/sev-guest: Remove the disable_vmpck label in handle_guest_request()")
Cc: <stable@kernel.org> # 0fdb6cc7c8 ("virt/coco/sev-guest: Carve out the request issuing logic into a helper")
Cc: <stable@kernel.org> # d25bae7dc7 ("virt/coco/sev-guest: Do some code style cleanups")
Cc: <stable@kernel.org> # fa4ae42cc6 ("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
Remove unnecessary linebreaks, make the code more compact.
No functional changes.
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20230307192449.24732-7-bp@alien8.de
This makes the code flow a lot easier to follow.
No functional changes.
[ Tom: touchups. ]
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230307192449.24732-6-bp@alien8.de
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) <bp@alien8.de>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230307192449.24732-4-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>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20230307192449.24732-3-bp@alien8.de
Commit
47894e0fa6 ("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: 47894e0fa6 ("virt/sev-guest: Prevent IV reuse in the SNP guest driver")
Reported-by: Larry Dewey <larry.dewey@amd.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Tested-by: Larry Dewey <larry.dewey@amd.com>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/2afbcae6daf13f7ad5a4296692e0a0fe1bc1e4ee.1677083979.git.thomas.lendacky@amd.com
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Merge tag 'x86_sev_for_v6.2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
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()
The AMD Secure Processor (ASP) and an SNP guest use a series of
AES-GCM keys called VMPCKs to communicate securely with each other.
The IV to this scheme is a sequence number that both the ASP and the
guest track.
Currently, this sequence number in a guest request must exactly match
the sequence number tracked by the ASP. This means that if the guest
sees an error from the host during a request it can only retry that
exact request or disable the VMPCK to prevent an IV reuse. AES-GCM
cannot tolerate IV reuse, see: "Authentication Failures in NIST version
of GCM" - Antoine Joux et al.
In order to address this, make handle_guest_request() delete the VMPCK
on any non successful return. To allow userspace querying the cert_data
length make handle_guest_request() save the number of pages required by
the host, then have handle_guest_request() retry the request without
requesting the extended data, then return the number of pages required
back to userspace.
[ bp: Massage, incorporate Tom's review comments. ]
Fixes: fce96cf044 ("virt: Add SEV-SNP guest driver")
Reported-by: Peter Gonda <pgonda@google.com>
Signed-off-by: Peter Gonda <pgonda@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: stable@kernel.org
Link: https://lore.kernel.org/r/20221116175558.2373112-1-pgonda@google.com
Fix a sparse warning in sev_guest_probe() where the wrong argument type is
provided to iounmap().
Fixes: fce96cf044 ("virt: Add SEV-SNP guest driver")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/202207150617.jqwQ0Rpz-lkp@intel.com
The GHCB specification section 2.7 states that when SEV-SNP is enabled,
a guest should not rely on the hypervisor to provide the address of the
AP jump table. Instead, if a guest BIOS wants to provide an AP jump
table, it should record the address in the SNP secrets page so the guest
operating system can obtain it directly from there.
Fix this on the guest kernel side by having SNP guests use the AP jump
table address published in the secrets page rather than issuing a GHCB
request to get it.
[ mroth:
- Improve error handling when ioremap()/memremap() return NULL
- Don't mix function calls with declarations
- Add missing __init
- Tweak commit message ]
Fixes: 0afb6b660a ("x86/sev: Use SEV-SNP AP creation to start secondary CPUs")
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220422135624.114172-3-michael.roth@amd.com
Dionna Glaze