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Date:   Wed, 21 Oct 2020 17:28:33 +0200
From:   Daniel Kiper <daniel.kiper@oracle.com>
To:     Arvind Sankar <nivedita@alum.mit.edu>
Cc:     Ross Philipson <ross.philipson@oracle.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        iommu@lists.linux-foundation.org, linux-integrity@vger.kernel.org,
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        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
        luto@amacapital.net, trenchboot-devel@googlegroups.com
Subject: Re: [PATCH 07/13] x86: Secure Launch kernel early boot stub
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On Mon, Oct 19, 2020 at 01:18:22PM -0400, Arvind Sankar wrote:
> On Mon, Oct 19, 2020 at 04:51:53PM +0200, Daniel Kiper wrote:
> > On Fri, Oct 16, 2020 at 04:51:51PM -0400, Arvind Sankar wrote:
> > > On Thu, Oct 15, 2020 at 08:26:54PM +0200, Daniel Kiper wrote:
> > > >
> > > > I am discussing with Ross the other option. We can create
> > > > .rodata.mle_header section and put it at fixed offset as
> > > > kernel_info is. So, we would have, e.g.:
> > > >
> > > > arch/x86/boot/compressed/vmlinux.lds.S:
> > > >         .rodata.kernel_info KERNEL_INFO_OFFSET : {
> > > >                 *(.rodata.kernel_info)
> > > >         }
> > > >         ASSERT(ABSOLUTE(kernel_info) == KERNEL_INFO_OFFSET, "kernel_info at bad address!")
> > > >
> > > >         .rodata.mle_header MLE_HEADER_OFFSET : {
> > > >                 *(.rodata.mle_header)
> > > >         }
> > > >         ASSERT(ABSOLUTE(mle_header) == MLE_HEADER_OFFSET, "mle_header at bad address!")
> > > >
> > > > arch/x86/boot/compressed/sl_stub.S:
> > > > #define mleh_rva(X) (((X) - mle_header) + MLE_HEADER_OFFSET)
> > > >
> > > >         .section ".rodata.mle_header", "a"
> > > >
> > > > SYM_DATA_START(mle_header)
> > > >         .long   0x9082ac5a    /* UUID0 */
> > > >         .long   0x74a7476f    /* UUID1 */
> > > >         .long   0xa2555c0f    /* UUID2 */
> > > >         .long   0x42b651cb    /* UUID3 */
> > > >         .long   0x00000034    /* MLE header size */
> > > >         .long   0x00020002    /* MLE version 2.2 */
> > > >         .long   mleh_rva(sl_stub_entry)    /* Linear entry point of MLE (virt. address) */
> > > >         .long   0x00000000    /* First valid page of MLE */
> > > >         .long   0x00000000    /* Offset within binary of first byte of MLE */
> > > >         .long   0x00000000    /* Offset within binary of last byte + 1 of MLE */
> > > >         .long   0x00000223    /* Bit vector of MLE-supported capabilities */
> > > >         .long   0x00000000    /* Starting linear address of command line (unused) */
> > > >         .long   0x00000000    /* Ending linear address of command line (unused) */
> > > > SYM_DATA_END(mle_header)
> > > >
> > > > Of course MLE_HEADER_OFFSET has to be defined as a constant somewhere.
> > > > Anyway, is it acceptable?
> >
> > What do you think about my MLE_HEADER_OFFSET and related stuff proposal?
> >
>
> I'm wondering if it would be easier to just allow relocations in these
> special "header" sections. I need to check how easy/hard it is to do
> that without triggering linker warnings.

Ross and I still bouncing some ideas. We came to the conclusion that
putting mle_header into kernel .rodata.kernel_info section or even
arch/x86/boot/compressed/kernel_info.S file would be the easiest thing
to do at this point. Of course I would suggest some renaming too. E.g.
.rodata.kernel_info to .rodata.kernel_headers, etc. Does it make sense
for you?

Daniel