On 02.05.2023 16:59, Roger Pau Monne wrote: > Ensure that the base address is 2M aligned, or else the page table > entries created would be corrupt as reserved bits on the PDE end up > set. > > We have encountered a broken firmware where grub2 would end up loading > Xen at a non 2M aligned region when using the multiboot2 protocol, and > that caused a very difficult to debug triple fault. > > If the alignment is not as required by the page tables print an error > message and stop the boot. Also add a build time check that the > calculation of symbol offsets don't break alignment of passed > addresses. > > The check could be performed earlier, but so far the alignment is > required by the page tables, and hence feels more natural that the > check lives near to the piece of code that requires it. > > Note that when booted as an EFI application from the PE entry point > the alignment check is already performed by > efi_arch_load_addr_check(), and hence there's no need to add another > check at the point where page tables get built in > efi_arch_memory_setup(). > > Signed-off-by: Roger Pau Monné <roger....@citrix.com>
Reviewed-by: Jan Beulich <jbeul...@suse.com> Would you mind if, while committing, ... > @@ -146,6 +148,9 @@ bad_cpu: > not_multiboot: > add $sym_offs(.Lbad_ldr_msg),%esi # Error message > jmp .Lget_vtb > +not_aligned: ... a .L prefix was added to this label, bringing it out of sync with the earlier one, but in line with e.g. ... > + add $sym_offs(.Lbag_alg_msg),%esi # Error message > + jmp .Lget_vtb > .Lmb2_no_st: ... this one? I don't think the label is particularly useful to have in the symbol table (nor are not_multiboot and likely a few others). Jan
