linux-kernel - tboot: non-0 tboot_addr but it is not of type E820

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Message-ID: <94D0CD8314A33A4D9D801C0FE68B40295BE5000E@G9W0745.americas.hpqcorp.net>
Date:	Tue, 24 Nov 2015 01:57:39 +0000
From:	"Elliott, Robert (Persistent Memory)" <elliott@....com>
To:	"joseph.cihula@...el.com" <joseph.cihula@...el.com>,
	"richard.l.maliszewski@...el.com" <richard.l.maliszewski@...el.com>,
	"gang.wei@...el.com" <gang.wei@...el.com>,
	"shane.wang@...el.com" <shane.wang@...el.com>
CC:	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
	"tboot-devel@...ts.sourceforge.net" 
	<tboot-devel@...ts.sourceforge.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Knippers, Linda" <linda.knippers@....com>,
	"Kani, Toshimitsu" <toshi.kani@....com>
Subject: tboot: non-0 tboot_addr but it is not of type E820_RESERVED

I noticed this being reported on our UEFI-based machines booting 
with grub2 (and not using trusted boot):
[    0.000000] tboot: non-0 tboot_addr but it is not of type E820_RESERVED

The alleged address is:
                0x6b7369642065766f
which is actually an ASCII string "ksid evo".

That comes from arch/c86/kernel/tboot.c checking if the address is
in the E820 table.

Is that supposed to be initialized to 0 by the EFI boot stub
in arch/x86/boot/compressed/eboot.c, and we're just lucky that it
doesn't appear to be a valid address?

void __init tboot_probe(void)
{
        /* Look for valid page-aligned address for shared page. */
        if (!boot_params.tboot_addr)
                return;
        /*
         * also verify that it is mapped as we expect it before calling
         * set_fixmap(), to reduce chance of garbage value causing crash
         */
        if (!e820_any_mapped(boot_params.tboot_addr,
                             boot_params.tboot_addr, E820_RESERVED)) {
                pr_warning("non-0 tboot_addr but it is not of type E820_RESERVED\n");
                return;
        }

That's part of this structure:
struct boot_params {
        struct screen_info screen_info;                 /* 0x000 */
       struct apm_bios_info apm_bios_info;             /* 0x040 */
        __u8  _pad2[4];                                 /* 0x054 */
        __u64  tboot_addr;                              /* 0x058 */
        struct ist_info ist_info;                       /* 0x060 */
...

---
Robert Elliott, HPE Persistent Memory

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