[Xen-devel] is_loadable_phdr

[Brad Plant <bplant@xxxxxxxxxxxx>]

Hi,

I'm attempting to boot the latest mainline kernel patched with PaX. The PaX 
patch marks some segments as read-only (R--) which is resulting in these 
segments not being loaded due to is_loadable_phdr returning zero for read-only 
segments:

int elf_phdr_is_loadable(struct elf_binary *elf, const elf_phdr * phdr)
{
        uint64_t p_type = elf_uval(elf, phdr, p_type);
        uint64_t p_flags = elf_uval(elf, phdr, p_flags);

        return ((p_type == PT_LOAD) && (p_flags & (PF_W | PF_X)) != 0);
}

I'm trying to get an understanding of why a segment has to be writeable or 
executable for xen to load it. Does anyone know why this is so?

Also, is it likely that this behaviour could be changed? My understanding is 
that it's perfectly valid to have an ELF kernel with read-only segments in it. 
Attempting to use an image with a read-only segment leads to the kernel failing 
to boot with weird and hard to debug crashes.

Cheers,

Brad

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