Re: Problem loading linux 5.19 as PV dom0

[Juergen Gross <jgross@xxxxxxxx>]

On 23.06.22 09:55, Jan Beulich wrote:
> On 22.06.2022 18:06, Juergen Gross wrote:
> > A Linux kernel 5.19 can only be loaded as dom0, if it has been
> > built with CONFIG_AMD_MEM_ENCRYPT enabled. This is due to the
> > fact that otherwise the (relevant) last section of the built
> > kernel has the NOLOAD flag set (it is still marked with
> > SHF_ALLOC).
> >
> > I think at least the hypervisor needs to be changed to support
> > this layout. Otherwise it will put the initial page tables for
> > dom0 at the same position as this last section, leading to
> > early crashes.
> Isn't Xen using the bzImage header there, rather than any ELF
> one? In which case it would matter how the NOLOAD section is
For a PV kernel? No, I don't think so. Just sent a patch repairing
the issue, BTW.

> actually represented in that header. Can you provide a dump (or
> binary representation) of both headers?
Program Header:
    LOAD off    0x0000000000200000 vaddr 0xffffffff81000000 paddr 
0x0000000001000000 align 2**21
         filesz 0x000000000145e114 memsz 0x000000000145e114 flags r-x
    LOAD off    0x0000000001800000 vaddr 0xffffffff82600000 paddr 
0x0000000002600000 align 2**21
         filesz 0x00000000006b7000 memsz 0x00000000006b7000 flags rw-
    LOAD off    0x0000000002000000 vaddr 0x0000000000000000 paddr 
0x0000000002cb7000 align 2**21
         filesz 0x00000000000312a8 memsz 0x00000000000312a8 flags rw-
    LOAD off    0x00000000020e9000 vaddr 0xffffffff82ce9000 paddr 
0x0000000002ce9000 align 2**21
         filesz 0x00000000001fd000 memsz 0x0000000000317000 flags rwx
    NOTE off    0x000000000165df10 vaddr 0xffffffff8245df10 paddr 
0x000000000245df10 align 2**2
         filesz 0x0000000000000204 memsz 0x0000000000000204 flags ---


Sections:
Idx Name          Size      VMA               LMA               File off  Algn
...
 30 .smp_locks    00009000  ffffffff82edc000  0000000002edc000  022dc000  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
 31 .data_nosave  00001000  ffffffff82ee5000  0000000002ee5000  022e5000  2**2
                  CONTENTS, ALLOC, LOAD, DATA
 32 .bss          0011a000  ffffffff82ee6000  0000000002ee6000  022e6000  2**12
                  ALLOC
 33 .brk          00026000  ffffffff83000000  ffffffff83000000  00000000  2**0
                  ALLOC

And the related linker script part:

        __end_of_kernel_reserve = .;

        . = ALIGN(PAGE_SIZE);
        .brk (NOLOAD) : AT(ADDR(.brk) - LOAD_OFFSET) {
                __brk_base = .;
                . += 64 * 1024;         /* 64k alignment slop space */
                *(.bss..brk)            /* areas brk users have reserved */
                __brk_limit = .;
        }

        . = ALIGN(PAGE_SIZE);           /* keep VO_INIT_SIZE page aligned */
        _end = .;


Juergen

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