APEI/GHES: ARM processor Error: don't go past allocated memory

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

APEI/GHES: ARM processor Error: don't go past allocated memory

If the BIOS generates a very small ARM Processor Error, or
an incomplete one, the current logic will fail to deferrence

err->section_length
and
ctx_info->size

Add checks to avoid that. With such changes, such GHESv2
records won't cause OOPSes like this:

[ 1.492129] Internal error: Oops: 0000000096000005 [#1] SMP
[ 1.495449] Modules linked in:
[ 1.495820] CPU: 0 UID: 0 PID: 9 Comm: kworker/0:0 Not tainted 6.18.0-rc1-00017-gabadcc3553dd-dirty #18 PREEMPT
[ 1.496125] Hardware name: QEMU QEMU Virtual Machine, BIOS unknown 02/02/2022
[ 1.496433] Workqueue: kacpi_notify acpi_os_execute_deferred
[ 1.496967] pstate: 814000c5 (Nzcv daIF +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[ 1.497199] pc : log_arm_hw_error+0x5c/0x200
[ 1.497380] lr : ghes_handle_arm_hw_error+0x94/0x220

0xffff8000811c5324 is in log_arm_hw_error (../drivers/ras/ras.c:75).
70 err_info = (struct cper_arm_err_info *)(err + 1);
71 ctx_info = (struct cper_arm_ctx_info *)(err_info + err->err_info_num);
72 ctx_err = (u8 *)ctx_info;
73
74 for (n = 0; n < err->context_info_num; n++) {
75 sz = sizeof(struct cper_arm_ctx_info) + ctx_info->size;
76 ctx_info = (struct cper_arm_ctx_info *)((long)ctx_info + sz);
77 ctx_len += sz;
78 }
79

and similar ones while trying to access section_length on an
error dump with too small size.

[ rjw: Subject tweaks ]