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x86/PVH: Support relocatable dom0 kernels
Xen tries to load a PVH dom0 kernel at the fixed guest physical address from the elf headers. For Linux, this defaults to 0x1000000 (16MB), but it can be configured. Unfortunately there exist firmwares that have reserved regions at this address, so Xen fails to load the dom0 kernel since it's not RAM. The PVH entry code is not relocatable - it loads from absolute addresses, which fail when the kernel is loaded at a different address. With a suitably modified kernel, a reloctable entry point is possible. Add XEN_ELFNOTE_PHYS32_RELOC which specifies optional alignment, minimum, and maximum addresses needed for the kernel. The presence of the NOTE indicates the kernel supports a relocatable entry path. Change the loading to check for an acceptable load address. If the kernel is relocatable, support finding an alternate load address. The primary motivation for an explicit align field is that Linux has a configurable CONFIG_PHYSICAL_ALIGN field. This value is present in the bzImage setup header, but not the ELF program headers p_align, which report 2MB even when CONFIG_PHYSICAL_ALIGN is greater. Since a kernel is only considered relocatable if the PHYS32_RELOC elf note is present, the alignment contraints can just be specified within the note instead of searching for an alignment value via a heuristic. Load alignment uses the PHYS32_RELOC note value if specified. Otherwise, the maxmum ELF PHDR p_align value is selected if greater than or equal to PAGE_SIZE. Finally, the fallback default is 2MB. libelf-private.h includes common-macros.h to satisfy the fuzzer build. Link: https://gitlab.com/xen-project/xen/-/issues/180 Signed-off-by: Jason Andryuk <jason.andryuk@amd.com> Reviewed-by: Jan Beulich <jbeulich@suse.com>
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