On 25 September 2015 at 23:01, Ingo Molnar <mingo@xxxxxxxxxx> wrote: > > * Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx> wrote: > >> From: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> >> >> The new Properties Table feature introduced in UEFIv2.5 may split >> memory regions that cover PE/COFF memory images into separate code >> and data regions. Since these regions only differ in the type (runtime >> code vs runtime data) and the permission bits, but not in the memory >> type attributes (UC/WC/WT/WB), the spec does not require them to be >> aligned to 64 KB. >> >> Since the relative offset of PE/COFF .text and .data segments cannot >> be changed on the fly, this means that we can no longer pad out those >> regions to be mappable using 64 KB pages. >> Unfortunately, there is no annotation in the UEFI memory map that >> identifies data regions that were split off from a code region, so we >> must apply this logic to all adjacent runtime regions whose attributes >> only differ in the permission bits. >> >> So instead of rounding each memory region to 64 KB alignment at both >> ends, only round down regions that are not directly preceded by another >> runtime region with the same type attributes. Since the UEFI spec does >> not mandate that the memory map be sorted, this means we also need to >> sort it first. > > So I think this is fundamentally wrong as well, similarly to the related x86 fix. > > I think for compatibility reasons the whole 'EFI runtime image' should be mapped > in a single go, as closely matching the EFI layouts and offsets as possible. We > are not talking about gigabytes here, right? > As I explained in the other thread, this is really not necessary, and never has been until the firmware started splitting up PE/COFF images into several sections each. As long as we keep those PE/COFF images together, everything will work as before, and the only complication is that the memory map does not contain any clues about which regions belong to a single PE/COFF image, so we need to keep all adjacent EFI_MEMORY_RUNTIME regions adjacent in the VA mapping. > Even if technically they are 'separate sections', the x86 bug shows that they > aren't. So we should not pretend so on the Linux side either and we should not > tear them apart (and then work hard to preserve the interdependencies, some > declared, some hidden!). > This is about relocations and interdependencies at the symbol level, and such interdependencies only exist internally inside PE/COFF images. > If we allocate the EFI runtime as a single virtual memory block then issues like > rounding between sections does not even come up as a problem: we map the original > offsets and sizes byte by byte. > Well, by that reasoning, we should not call SetVirtualAddressMap() in the first place, and just use the 1:1 mapping UEFI uses natively. This is more than feasible on arm64, and I actually fought hard against using SetVirtualAddressMap() at all, but I was overruled by others. I think this is also trivially possible on X64, since the 1:1 mapping is already active alongside the VA mapping. -- Ard. -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
