Re: [PATCH 07/13] x86: Secure Launch kernel early boot stub

[Arvind Sankar]

On Mon, Oct 19, 2020 at 10:38:08AM -0400, Ross Philipson wrote:
> On 10/16/20 4:51 PM, 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?
> >>
> >> 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
> 
> It is the size of the protected mode image. Though how to reference
> those symbols to get the size might all more relocation issues.
> 

Ok, then I think mleh_rva(_edata) should get you that -- I assume you
don't want to include the uninitialized data in the size? The kernel
will access memory beyond _edata (upto the init_size in the setup
header), but that's not part of the image itself.