On Fri, Apr 12, 2024 at 06:19:40PM -0400, Steven Rostedt wrote: > On Fri, 12 Apr 2024 23:59:07 +0300 > Mike Rapoport <rppt@xxxxxxxxxx> 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 <keescook@xxxxxxxxxxxx> 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(). -- Kees Cook
