APEI/GHES: ensure that won't go past CPER allocated record

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

APEI/GHES: ensure that won't go past CPER allocated record

The logic at ghes_new() prevents allocating too large records, by
checking if they're bigger than GHES_ESTATUS_MAX_SIZE (currently, 64KB).
Yet, the allocation is done with the actual number of pages from the
CPER bios table location, which can be smaller.

Yet, a bad firmware could send data with a different size, which might
be bigger than the allocated memory, causing an OOPS:

Unable to handle kernel paging request at virtual address fff00000f9b40000
Mem abort info:
ESR = 0x0000000096000007
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x07: level 3 translation fault
Data abort info:
ISV = 0, ISS = 0x00000007, ISS2 = 0x00000000
CM = 0, WnR = 0, TnD = 0, TagAccess = 0
GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
swapper pgtable: 4k pages, 52-bit VAs, pgdp=000000008ba16000
[fff00000f9b40000] pgd=180000013ffff403, p4d=180000013fffe403, pud=180000013f85b403, pmd=180000013f68d403, pte=0000000000000000
Internal error: Oops: 0000000096000007 [#1] SMP
Modules linked in:
CPU: 0 UID: 0 PID: 303 Comm: kworker/0:1 Not tainted 6.19.0-rc1-00002-gda407d200220 #34 PREEMPT
Hardware name: QEMU QEMU Virtual Machine, BIOS unknown 02/02/2022
Workqueue: kacpi_notify acpi_os_execute_deferred
pstate: 214020c5 (nzCv daIF +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
pc : hex_dump_to_buffer+0x30c/0x4a0
lr : hex_dump_to_buffer+0x328/0x4a0
sp : ffff800080e13880
x29: ffff800080e13880 x28: ffffac9aba86f6a8 x27: 0000000000000083
x26: fff00000f9b3fffc x25: 0000000000000004 x24: 0000000000000004
x23: ffff800080e13905 x22: 0000000000000010 x21: 0000000000000083
x20: 0000000000000001 x19: 0000000000000008 x18: 0000000000000010
x17: 0000000000000001 x16: 00000007c7f20fec x15: 0000000000000020
x14: 0000000000000008 x13: 0000000000081020 x12: 0000000000000008
x11: ffff800080e13905 x10: ffff800080e13988 x9 : 0000000000000000
x8 : 0000000000000000 x7 : 0000000000000001 x6 : 0000000000000020
x5 : 0000000000000030 x4 : 00000000fffffffe x3 : 0000000000000000
x2 : ffffac9aba78c1c8 x1 : ffffac9aba76d0a8 x0 : 0000000000000008
Call trace:
hex_dump_to_buffer+0x30c/0x4a0 (P)
print_hex_dump+0xac/0x170
cper_estatus_print_section+0x90c/0x968
cper_estatus_print+0xf0/0x158
__ghes_print_estatus+0xa0/0x148
ghes_proc+0x1bc/0x220
ghes_notify_hed+0x5c/0xb8
notifier_call_chain+0x78/0x148
blocking_notifier_call_chain+0x4c/0x80
acpi_hed_notify+0x28/0x40
acpi_ev_notify_dispatch+0x50/0x80
acpi_os_execute_deferred+0x24/0x48
process_one_work+0x15c/0x3b0
worker_thread+0x2d0/0x400
kthread+0x148/0x228
ret_from_fork+0x10/0x20
Code: 6b14033f 540001ad a94707e2 f100029f (b8747b44)
---[ end trace 0000000000000000 ]---

Prevent that by taking the actual allocated are into account when
checking for CPER length.

[ rjw: Subject tweaks ]