EFI/CPER: don't go past the ARM processor CPER record buffer

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

EFI/CPER: don't go past the ARM processor CPER record buffer

There's a logic inside GHES/CPER to detect if the section_length

is too small, but it doesn't detect if it is too big.

Currently, if the firmware receives an ARM processor CPER record

stating that a section length is big, kernel will blindly trust

section_length, producing a very long dump. For instance, a 67

bytes record with ERR_INFO_NUM set 46198 and section length

set to 854918320 would dump a lot of data going a way past the

firmware memory-mapped area.

Fix it by adding a logic to prevent it to go past the buffer

if ERR_INFO_NUM is too big, making it report instead:

[Hardware Error]: Hardware error from APEI Generic Hardware Error Source: 1

[Hardware Error]: event severity: recoverable

[Hardware Error]: Error 0, type: recoverable

[Hardware Error]: section_type: ARM processor error

[Hardware Error]: MIDR: 0xff304b2f8476870a

[Hardware Error]: section length: 854918320, CPER size: 67

[Hardware Error]: section length is too big

[Hardware Error]: firmware-generated error record is incorrect

[Hardware Error]: ERR_INFO_NUM is 46198

[ rjw: Subject and changelog tweaks ]