linux-kernel - Re: [PATCH 08/62] x86/boot/compressed/64: Add IDT Infrastructure

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Date:   Wed, 12 Feb 2020 12:19:24 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Linux Virtualization <virtualization@...ts.linux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 08/62] x86/boot/compressed/64: Add IDT Infrastructure

Hi Andy,

thanks a lot for your valuable reviews!

On Tue, Feb 11, 2020 at 02:18:52PM -0800, Andy Lutomirski wrote:
> On Tue, Feb 11, 2020 at 5:53 AM Joerg Roedel <joro@...tes.org> wrote:
> > +       entry.offset_low    = (u16)(address & 0xffff);
> > +       entry.segment       = __KERNEL_CS;
> > +       entry.bits.type     = GATE_TRAP;
> 
> ^^^
> 
> I realize we're not running a real kernel here, but GATE_TRAP is
> madness.  Please use GATE_INTERRUPT.

Changed that.

> > +       /* Build pt_regs */
> > +       .if \error_code == 0
> > +       pushq   $0
> > +       .endif
> 
> cld

Added.

> > +       popq    %rdi
> 
> if error_code?

The code above pushes a $0 for exceptions without an error code, so it
needs to be removed unconditionally.

> > +
> > +       /* Remove error code and return */
> > +       addq    $8, %rsp
> > +
> > +       /*
> > +        * Make sure we return to __KERNEL_CS - the CS selector on
> > +        * the IRET frame might still be from an old BIOS GDT
> > +        */
> > +       movq    $__KERNEL_CS, 8(%rsp)
> > +
> 
> If this actually happens, you have a major bug.  Please sanitize all
> the segment registers after installing the GDT rather than hacking
> around it here.

Okay, will change that. I thought I could safe some instructions in the
head_64.S code, but you are right that its better to setup a defined
environment first.


Thanks,

	Joerg