On Tue, Oct 22, 2019 at 6:15 PM Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote: > > On Tue, 22 Oct 2019 at 09:45, Borislav Petkov <bp@xxxxxxxxx> wrote: > > > > On Tue, Oct 22, 2019 at 08:13:56AM +0200, Ard Biesheuvel wrote: > > > On Thu, 17 Oct 2019 at 11:30, Kairui Song <kasong@xxxxxxxxxx> wrote: > > > > > > > > Currently, kernel fails to boot on some HyperV VMs when using EFI. > > > > And it's a potential issue on all platforms. > > > > > > > > It's caused by broken kernel relocation on EFI systems, when below three > > > > conditions are met: > > > > > > > > 1. Kernel image is not loaded to the default address (LOAD_PHYSICAL_ADDR) > > > > by the loader. > > > > 2. There isn't enough room to contain the kernel, starting from the > > > > default load address (eg. something else occupied part the region). > > > > 3. In the memmap provided by EFI firmware, there is a memory region > > > > starts below LOAD_PHYSICAL_ADDR, and suitable for containing the > > > > kernel. > > > > > > > > EFI stub will perform a kernel relocation when condition 1 is met. But > > > > due to condition 2, EFI stub can't relocate kernel to the preferred > > > > address, so it fallback to ask EFI firmware to alloc lowest usable memory > > > > region, got the low region mentioned in condition 3, and relocated > > > > kernel there. > > > > > > > > It's incorrect to relocate the kernel below LOAD_PHYSICAL_ADDR. This > > > > is the lowest acceptable kernel relocation address. > > > > > > > > The first thing goes wrong is in arch/x86/boot/compressed/head_64.S. > > > > Kernel decompression will force use LOAD_PHYSICAL_ADDR as the output > > > > address if kernel is located below it. Then the relocation before > > > > decompression, which move kernel to the end of the decompression buffer, > > > > will overwrite other memory region, as there is no enough memory there. > > > > > > > > To fix it, just don't let EFI stub relocate the kernel to any address > > > > lower than lowest acceptable address. > > > > > > > > Signed-off-by: Kairui Song <kasong@xxxxxxxxxx> > > > > Acked-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx> > > > > > > > > > > Ingo, Boris, could you please comment on this? > > > > Yah, the commit message makes more sense now. > > > > > Thanks Boris. > > Kairui, I will apply the requested changes myself - no need to spin a v5 Thanks for review and the suggestion, that change is a good idea. -- Best Regards, Kairui Song
