On Mon, Apr 15, 2024 at 10:22:53AM -0700, Kees Cook wrote: > On Fri, Apr 12, 2024 at 06:19:40PM -0400, Steven Rostedt wrote: > > On Fri, 12 Apr 2024 23:59:07 +0300 > > Mike Rapoport <r...@kernel.org> wrote: > > > > > On Tue, Apr 09, 2024 at 04:41:24PM -0700, Kees Cook wrote: > > > > On Tue, Apr 09, 2024 at 07:11:56PM -0400, Steven Rostedt wrote: > > > > > On Tue, 9 Apr 2024 15:23:07 -0700 > > > > > Kees Cook <keesc...@chromium.org> wrote: > > > > > > > > > > > Do we need to involve e820 at all? I think it might be possible to > > > > > > just > > > > > > have pstore call request_mem_region() very early? Or does KASLR make > > > > > > that unstable? > > > > > > > > > > Yeah, would that give the same physical memory each boot, and can we > > > > > guarantee that KASLR will not map the kernel over the previous > > > > > location? > > > > > > > > Hm, no, for physical memory it needs to get excluded very early, which > > > > means e820. > > > > > > Whatever memory is reserved in arch/x86/kernel/e820.c, that happens after > > > kaslr, so to begin with, a new memmap parameter should be also added to > > > parse_memmap in arch/x86/boot/compressed/kaslr.c to ensure the same > > > physical address will be available after KASLR. > > > > But doesn't KASLR only affect virtual memory not physical memory? > > KASLR for x86 (and other archs, like arm64) do both physical and virtual > base randomization. > > > This just makes sure the physical memory it finds will not be used by the > > system. Then ramoops does the mapping via vmap() I believe, to get a > > virtual address to access the physical address. > > I was assuming, since you were in the e820 code, that it was > manipulating that before KASLR chose a location. But if not, yeah, Mike > is right -- you need to make sure this is getting done before > decompress_kernel().
Right now kaslr can handle up to 4 memmap regions and parse_memmap() in arch/x86/boot/compressed/kaslr.c should be updated for a new memmap type. But I think it's better to add a new kernel parameter as I suggested in another email and teach mem_avoid_memmap() in kaslr.c to deal with it, as well as with crashkernel=size@offset, btw. > -- > Kees Cook -- Sincerely yours, Mike.
