grub: fix CVE-2020-14372 and CVE-2020-27779

grub: fix CVE-2020-14372 and CVE-2020-27779

Fix issues with grub in secure boot mode where an attacker could circumvent
secure boot by using acpi and cutmem commands. Also include patches fixing
similar issues.

Most patches are backported directly from grub. One patch
(no-insmod-on-sb.patch) comes from Debian, as the upstream implementation is
too complicated to backport.

CVE-2020-14372 description (from NVD [1]):
A flaw was found in grub2 in versions prior to 2.06, where it incorrectly
enables the usage of the ACPI command when Secure Boot is enabled.
This flaw allows an attacker with privileged access to craft a Secondary
System Description Table (SSDT) containing code to overwrite the Linux
kernel lockdown variable content directly into memory. The table is
further loaded and executed by the kernel, defeating its Secure Boot
lockdown and allowing the attacker to load unsigned code. The highest
threat from this vulnerability is to data confidentiality and integrity,
as well as system availability.

CVE-2020-27779 description (from NVD [2]):
A flaw was found in grub2 in versions prior to 2.06. The cutmem command
does not honor secure boot locking allowing an privileged attacker to
remove address ranges from memory creating an opportunity to circumvent
SecureBoot protections after proper triage about grub's memory layout.
The highest threat from this vulnerability is to data confidentiality
and integrity as well as system availability.

[1] https://nvd.nist.gov/vuln/detail/CVE-2020-14372
[2] https://nvd.nist.gov/vuln/detail/CVE-2020-27779

Signed-off-by: Marta Rybczynska <marta.rybczynska@huawei.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>