Re: [PATCH] acpi: skip NULL entries in RSDT and XSDT

[Daniel Kiper]

On Mon, Sep 25, 2023 at 01:58:18PM +0800, Michael Chang via Grub-devel wrote:
> During attempts to configure a serial console, a Page Fault Exception
> and system reset were encountered, specifically on release 2.12-rc1.
> This issue was not present in prior versions and seemed to affect only a
> specific machine, potentially pointing to hardware or firmware flaw.
>
> After investigation, it was discovered that the invalid page access
> occurred during the discovery of serial MMIO ports as specified by
> ACPI's SPCR table [1]. The recent change uncovered an issue in Grub's
> ACPI driver.
>
> In certain cases, the XSDT/RSDT root table might contain a null entry as
> a terminator, depending on how the tables are assembled. Grub cannot
> blindly trust the address in the root table to be valid and should
> perform a sanity check for null entries. This patch introduces this
> simple check.
>
> This fix is also inspired by a related Linux kernel fix [2]:
>
> [1] 7b192ec4c term/ns8250: Use ACPI SPCR table when available to configure 
> serial
> [2] 0f929fbf0 ACPICA: Tables: Add new mechanism to skip NULL entries in RSDT 
> and XSDT.
>
> Signed-off-by: Michael Chang <mchang@suse.com>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Daniel