crypto: ccp - Always pass in an error pointer to __sev_platform_shutdown_locked()

In the Linux kernel, the following vulnerability has been resolved:

crypto: ccp - Always pass in an error pointer to __sev_platform_shutdown_locked()

When

9770b428b1a2 ("crypto: ccp - Move dev_info/err messages for SEV/SNP init and shutdown")

moved the error messages dumping so that they don't need to be issued by
the callers, it missed the case where __sev_firmware_shutdown() calls
__sev_platform_shutdown_locked() with a NULL argument which leads to
a NULL ptr deref on the shutdown path, during suspend to disk:

#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: Oops: 0000 [#1] SMP NOPTI
CPU: 0 UID: 0 PID: 983 Comm: hib.sh Not tainted 6.17.0-rc4+ #1 PREEMPT(voluntary)
Hardware name: Supermicro Super Server/H12SSL-i, BIOS 2.5 09/08/2022
RIP: 0010:__sev_platform_shutdown_locked.cold+0x0/0x21 [ccp]

That rIP is:

00000000000006fd <__sev_platform_shutdown_locked.cold>:
6fd: 8b 13 mov (%rbx),%edx
6ff: 48 8b 7d 00 mov 0x0(%rbp),%rdi
703: 89 c1 mov %eax,%ecx

Code: 74 05 31 ff 41 89 3f 49 8b 3e 89 ea 48 c7 c6 a0 8e 54 a0 41 bf 92 ff ff ff e8 e5 2e 09 e1 c6 05 2a d4 38 00 01 e9 26 af ff ff <8b> 13 48 8b 7d 00 89 c1 48 c7 c6 18 90 54 a0 89 44 24 04 e8 c1 2e
RSP: 0018:ffffc90005467d00 EFLAGS: 00010282
RAX: 00000000ffffff92 RBX: 0000000000000000 RCX: 0000000000000000
^^^^^^^^^^^^^^^^
and %rbx is nice and clean.

Call Trace:
<TASK>
__sev_firmware_shutdown.isra.0
sev_dev_destroy
psp_dev_destroy
sp_destroy
pci_device_shutdown
device_shutdown
kernel_power_off
hibernate.cold
state_store
kernfs_fop_write_iter
vfs_write
ksys_write
do_syscall_64
entry_SYSCALL_64_after_hwframe

Pass in a pointer to the function-local error var in the caller.

With that addressed, suspending the ccp shows the error properly at
least:

ccp 0000:47:00.1: sev command 0x2 timed out, disabling PSP
ccp 0000:47:00.1: SEV: failed to SHUTDOWN error 0x0, rc -110
SEV-SNP: Leaking PFN range 0x146800-0x146a00
SEV-SNP: PFN 0x146800 unassigned, dumping non-zero entries in 2M PFN region: [0x146800 - 0x146a00]
...
ccp 0000:47:00.1: SEV-SNP firmware shutdown failed, rc -16, error 0x0
ACPI: PM: Preparing to enter system sleep state S5
kvm: exiting hardware virtualization
reboot: Power down

Btw, this driver is crying to be cleaned up to pass in a proper I/O
struct which can be used to store information between the different
functions, otherwise stuff like that will happen in the future again.