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Date:   Mon, 19 Oct 2020 16:51:53 +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 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?

> > There is also another problem. We have to put into mle_header size of
> > the Linux kernel image. Currently it is done by the bootloader but
> > I think it is not a role of the bootloader. The kernel image should
> > provide all data describing its properties and do not rely on the
> > bootloader to do that. Ross and I investigated various options but we
> > did not find a good/simple way to do that. Could you suggest how we
> > should do that or at least where we should take a look to get some
> > ideas?
> >
> > Daniel
>
> What exactly is the size you need here? Is it just the size of the
> protected mode image, that's startup_32 to _edata. Or is it the size of
> the whole bzImage file, or something else? I guess the same question
> applies to "first valid page of MLE" and "first byte of MLE", and the
> linear entry point -- are those all relative to startup_32 or do they
> need to be relative to the start of the bzImage, i.e. you have to add
> the size of the real-mode boot stub?
>
> If you need to include the size of the bzImage file, that's not known
> when the files in boot/compressed are built. It's only known after the
> real-mode stub is linked. arch/x86/boot/tools/build.c fills in various
> details in the setup header and creates the bzImage file, but it does
> not currently modify anything in the protected-mode portion of the
> compressed kernel (i.e. arch/x86/boot/compressed/vmlinux, which then
> gets converted to binary format as arch/x86/boot/vmlinux.bin), so it
> would need to be extended if you need to modify the MLE header to
> include the bzImage size or anything depending on the size of the
> real-mode stub.

Ross clarified this. So, I not have to add much here.

Daniel