On 09/05/14 at 10:16am, Kees Cook wrote: > On Fri, Sep 5, 2014 at 7:08 AM, Baoquan He <[email protected]> wrote: > > diff --git a/arch/x86/boot/compressed/misc.c > > b/arch/x86/boot/compressed/misc.c > > index 7780a5b..d2a0eaa 100644 > > --- a/arch/x86/boot/compressed/misc.c > > +++ b/arch/x86/boot/compressed/misc.c > > @@ -250,6 +250,11 @@ static void handle_relocations(void *output, unsigned > > long output_len) > > } > > #endif > > > > + if (max_addr > CONFIG_RANDOMIZE_BASE_MAX_OFFSET) { > > + debug_putstr("Random addr is not allowed. No relocation > > needed... \n"); > > + return; > > + } > > + > > It's not clear to me what this is fixing. In aslr.c, > process_e820_entry() should already make it impossible to select > max_addr > CONFIG_RANDOMIZE_BASE_MAX_OFFSET. If you're trying to > detect a non-kaslr boot, I think this is better handled in 1/4 where I > suggest examining the "output" location before/after > choose_kernel_location. > > -Kees
Hi Kees, Yes, process_e820_entry() can make sure the choice+output_len < CONFIG_RANDOMIZE_BASE_MAX_OFFSET, but that can't stop other bootloaders to put kernel in region above CONFIG_RANDOMIZE_BASE_MAX_OFFSET. E.g in kdump, we can set crashkernel=256M@1024M in cmdline. Then the 1st kernel will reserve 256M memory just at 1024M place. So if load kdump kernel now, the output will be 1024M before choose_kernel_location(). With this value, output won't be changed in choose_kernel_location(), then it will do decompress(), then call handle_relocations(). Then since 1024 is not equal to LOAD_PHYSICAL_ADDR, it will start relocatoins handling. And this cause _text stamping into MODULES vaddr range. System will be exceptional. Thanks Baoquan > > > /* > > * Calculate the delta between where vmlinux was linked to load > > * and where it was actually loaded. > > -- > > 1.8.5.3 > > > > > > -- > Kees Cook > Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
