linux-kernel - Re: Early EFI-related boot freeze in parse_setup

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Tue, 27 Aug 2019 14:23:39 +0800
From:   Daniel Drake <drake@...lessm.com>
To:     linux-efi@...r.kernel.org,
        Linux Kernel <linux-kernel@...r.kernel.org>, x86@...nel.org
Cc:     Linux Upstreaming Team <linux@...lessm.com>
Subject: Re: Early EFI-related boot freeze in parse_setup_data()

On Fri, Aug 16, 2019 at 2:14 PM Daniel Drake <drake@...lessm.com> wrote:
> Anyway, the system freeze occurs in parse_setup_data(), specifically:
>
>         data = early_memremap(pa_data, sizeof(*data));
>         data_len = data->len + sizeof(struct setup_data);
>
> Dereferencing data->len causes the system to hang. I presume it
> triggers an exception handler due to some kind of invalid memory
> access.
>
> By returning early in that function, boot continues basically fine. So
> I could then log the details: pa_data has value 0x892bb018 and
> early_memremap returns address 0xffffffffff200018. Accessing just a
> single byte at that address causes the system hang.

I noticed a complaint about NX in the logs, right where it does the
early_memremap of this data (which is now at address 0x893c0018):

 Notice: NX (Execute Disable) protection missing in CPU!
 e820: update [mem 0x893c0018-0x893cec57] usable ==> usable
 e820: update [mem 0x893c0018-0x893cec57] usable ==> usable
 e820: update [mem 0x893b3018-0x893bf057] usable ==> usable
 e820: update [mem 0x893b3018-0x893bf057] usable ==> usable

Indeed, in the BIOS setup menu, "NX Mode" was Disabled.
Setting it to Enabled avoids the hang and Linux boots as normal. Weird!

Daniel