linux-kernel - Re: [PATCH 5/5] x86/head/64: Disable stack protection for head$(BITS).o

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Date:   Thu, 8 Oct 2020 10:42:19 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] x86/head/64: Disable stack protection for
 head$(BITS).o

On Wed, Oct 07, 2020 at 03:53:51PM -0400, Arvind Sankar wrote:
> On 64-bit, the startup_64_setup_env() function added in
>   866b556efa12 ("x86/head/64: Install startup GDT")
> has stack protection enabled because of set_bringup_idt_handler().
> 
> At this point, %gs is not yet initialized, and this doesn't cause a
> crash only because the #PF handler from the decompressor stub is still
> installed and handles the page fault.

Hmm, that is weird. Can you please share your config with which this
happens? I have a commit in my local branch which disables page-faulting
in the pre-decompression code before jumping to the uncompressed kernel
image, and it did not break anything here.

Also, what compiler did you use to trigger this?