Hi Akashi, On 24/07/18 07:57, AKASHI Takahiro wrote: > Adding "kaslr-seed" to dtb enables triggering kaslr, or kernel virtual > address randomization, at secondary kernel boot. Hmm, there are three things that get moved by CONFIG_RANDOMIZE_BASE. The kernel physical placement when booted via the EFIstub, the kernel-text VAs and the location of memory in the linear-map region. Adding the kaslr-seed only does the last two. This means the physical placement of the new kernel is predictable from /proc/iomem ... but this also tells you the physical placement of the current kernel, so I don't think this is a problem. > We always do this as it will have no harm on kaslr-incapable kernel. > We don't have any "switch" to turn off this feature directly, but still > can suppress it by passing "nokaslr" as a kernel boot argument. > diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c > index 7356da5a53d5..47a4fbd0dc34 100644 > --- a/arch/arm64/kernel/machine_kexec_file.c > +++ b/arch/arm64/kernel/machine_kexec_file.c > @@ -158,6 +160,12 @@ static int setup_dtb(struct kimage *image, Don't you need to reserve some space in the area you vmalloc()d for the DT? > + /* add kaslr-seed */ > + get_random_bytes(&value, sizeof(value)); What happens if the crng isn't ready? It looks like this will print a warning that these random-bytes aren't really up to standard, but the new kernel doesn't know this happened. crng_ready() isn't exposed, all we could do now is wait_for_random_bytes(), but that may wait forever because we do this unconditionally. I'd prefer to leave this feature until we can check crng_ready(), and skip adding a dodgy-seed if its not-ready. This avoids polluting the next-kernel's entropy pool. > + ret = fdt_setprop(buf, nodeoffset, "kaslr-seed", &value, sizeof(value)); Nit: It would be nice if this string were in a header file somewhere, to void future refactoring typos. Thanks, James _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
