tboot: non-0 tboot_addr but it is not of type E820_RESERVED

tboot: non-0 tboot_addr but it is not of type E820_RESERVED

[Elliott, Robert (Persistent Memory)]

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

RE: tboot: non-0 tboot_addr but it is not of type E820_RESERVED

[Elliott, Robert (Persistent Memory)]

> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-
> owner@vger.kernel.org] On Behalf Of Elliott, Robert (Persistent Memory)
> Sent: Monday, November 23, 2015 7:58 PM
...
> 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?
... 

Per an hpa suggestion, I compared two versions of grub:

upstream grub (with "linux" in grub.cfg):
tboot_probe boot_params[0] = 0000008000000000 0000000000000070 
tboot_probe boot_params[16] = 1000000400032000 0000009100003000 
tboot_probe boot_params[32] = 3fa3001000100810 0808080008180000 
tboot_probe boot_params[48] = 0000000000000000 0000000000000000 
tboot probe boot_params[64] = 0000000000000000 0000000000000000 
tboot_probe boot_params[80] = 0000000000000000 0000000000000000 
tboot_probe boot_params[96] = 0000000000000000 0000000000000000 
tboot_probe boot_params[112] = 0000000000000000 0000000000000000 
tboot_probe boot_params[128] = 0000000000000000 0000000000000000 
tboot_probe boot_params[144] = 0000000000000000 0000000000000000 
tboot_probe boot_params[160] = 0000000000000000 0000000000000000 
tboot_probe boot_params[176] = 0000000000000000 0000000000000000 
tboot_probe boot_params[192] = 0000000000000000 0000000000000000 
...
<no complaint about tboot_addr>

Fedora 22 grub (with "linuxefi" in grub.cfg):
tboot_probe boot_params[0] = 0000000000000000 0000000000000070
tboot_probe boot_params[16] = 0000000400032000 0000009100003000
tboot_probe boot_params[32] = 0000000000100810 0808080008180000
tboot_probe boot_params[48] = 0000010000000100 0000000000000000
tboot_probe boot_params[64] = 557365206120626f 6f74206c6f616465
tboot_probe boot_params[80] = 722e0d0a0a52656d 6f7665206469736b
tboot_probe boot_params[96] = 20616e6420707265 737320616e79206b
tboot_probe boot_params[112] = 657920746f207265 626f6f742e2e2e0d
tboot_probe boot_params[128] = 0a00504500006486 0400000000000000
tboot_probe boot_params[144] = 000001000000a000 06020b020214f017
tboot_probe boot_params[160] = 5c00000000001076 d200104600000002
tboot_probe boot_params[176] = 0000000000000000 0000200000002000
tboot_probe boot_params[192] = 0000000000000000 0000000000000000
...
[    0.000000] tboot: non-0 tboot_addr 0x6b7369642065766f but it is not of type E820_RESERVED

In both cases, the kernel is compiled with CONFIG_EFI_STUB=y.

tboot_addr is at offset 88.  Offset 64 is an ASCII string that says:
"Use a boot loader.

Remove disk and press any key to reboot..."

and is from arch/x86/boot/header.S, which is placing that string 
at offset 64 (0x3c + 4) from .bstext (which precedes .bsdata) if
CONFIG_EFI_STUB is true.

#ifdef CONFIG_EFI_STUB
        .org    0x3c
        #
        # Offset to the PE header.
        #
        .long   pe_header
#endif /* CONFIG_EFI_STUB */

        .section ".bsdata", "a"
bugger_off_msg:
        .ascii  "Use a boot loader.\r\n"
        .ascii  "\n"
        .ascii  "Remove disk and press any key to reboot...\r\n"
        .byte   0

Re: tboot: non-0 tboot_addr but it is not of type E820_RESERVED

[H. Peter Anvin]

On 12/01/15 17:26, Elliott, Robert (Persistent Memory) wrote:
>
> Per an hpa suggestion, I compared two versions of grub:
>
> upstream grub (with "linux" in grub.cfg):
> tboot_probe boot_params[0] = 0000008000000000 0000000000000070
> tboot_probe boot_params[16] = 1000000400032000 0000009100003000
> tboot_probe boot_params[32] = 3fa3001000100810 0808080008180000
> tboot_probe boot_params[48] = 0000000000000000 0000000000000000
> tboot probe boot_params[64] = 0000000000000000 0000000000000000
> tboot_probe boot_params[80] = 0000000000000000 0000000000000000
> tboot_probe boot_params[96] = 0000000000000000 0000000000000000
> tboot_probe boot_params[112] = 0000000000000000 0000000000000000
> tboot_probe boot_params[128] = 0000000000000000 0000000000000000
> tboot_probe boot_params[144] = 0000000000000000 0000000000000000
> tboot_probe boot_params[160] = 0000000000000000 0000000000000000
> tboot_probe boot_params[176] = 0000000000000000 0000000000000000
> tboot_probe boot_params[192] = 0000000000000000 0000000000000000
> ...
> <no complaint about tboot_addr>
>
> Fedora 22 grub (with "linuxefi" in grub.cfg):
> tboot_probe boot_params[0] = 0000000000000000 0000000000000070
> tboot_probe boot_params[16] = 0000000400032000 0000009100003000
> tboot_probe boot_params[32] = 0000000000100810 0808080008180000
> tboot_probe boot_params[48] = 0000010000000100 0000000000000000
> tboot_probe boot_params[64] = 557365206120626f 6f74206c6f616465
> tboot_probe boot_params[80] = 722e0d0a0a52656d 6f7665206469736b
> tboot_probe boot_params[96] = 20616e6420707265 737320616e79206b
> tboot_probe boot_params[112] = 657920746f207265 626f6f742e2e2e0d
> tboot_probe boot_params[128] = 0a00504500006486 0400000000000000
> tboot_probe boot_params[144] = 000001000000a000 06020b020214f017
> tboot_probe boot_params[160] = 5c00000000001076 d200104600000002
> tboot_probe boot_params[176] = 0000000000000000 0000200000002000
> tboot_probe boot_params[192] = 0000000000000000 0000000000000000
> ...
> [    0.000000] tboot: non-0 tboot_addr 0x6b7369642065766f but it is not of type E820_RESERVED
>
> In both cases, the kernel is compiled with CONFIG_EFI_STUB=y.
>
> tboot_addr is at offset 88.  Offset 64 is an ASCII string that says:
> "Use a boot loader.
>
> Remove disk and press any key to reboot..."
>
> and is from arch/x86/boot/header.S, which is placing that string
> at offset 64 (0x3c + 4) from .bstext (which precedes .bsdata) if
> CONFIG_EFI_STUB is true.
>
> #ifdef CONFIG_EFI_STUB
>          .org    0x3c
>          #
>          # Offset to the PE header.
>          #
>          .long   pe_header
> #endif /* CONFIG_EFI_STUB */
>
>          .section ".bsdata", "a"
> bugger_off_msg:
>          .ascii  "Use a boot loader.\r\n"
>          .ascii  "\n"
>          .ascii  "Remove disk and press any key to reboot...\r\n"
>          .byte   0
>

Most likely the "linuxefi" boot method uses the EFI handover protocol, 
however.  It looks like they don't start with a properly zeroed structure...