Re: [PATCH v6 00/12] implement KASLR for powerpc/fsl_booke/32

[Jason Yan]

On 2019/8/28 12:05, Scott Wood wrote:
> On Fri, 2019-08-09 at 18:07 +0800, Jason Yan wrote:
> > This series implements KASLR for powerpc/fsl_booke/32, as a security
> > feature that deters exploit attempts relying on knowledge of the location
> > of kernel internals.
> >
> > Since CONFIG_RELOCATABLE has already supported, what we need to do is
> > map or copy kernel to a proper place and relocate.
>
> Have you tested this with a kernel that was loaded at a non-zero address?  I
> tried loading a kernel at 0x04000000 (by changing the address in the uImage,
> and setting bootm_low to 04000000 in U-Boot), and it works without
> CONFIG_RANDOMIZE and fails with.

Not yet. I will test this kind of cases in the next days. Thank you so
much. If there are any other corner cases that have to be tested, please
let me know.

> >   Freescale Book-E
> > parts expect lowmem to be mapped by fixed TLB entries(TLB1). The TLB1
> > entries are not suitable to map the kernel directly in a randomized
> > region, so we chose to copy the kernel to a proper place and restart to
> > relocate.
> >
> > Entropy is derived from the banner and timer base, which will change every
> > build and boot. This not so much safe so additionally the bootloader may
> > pass entropy via the /chosen/kaslr-seed node in device tree.
>
> How complicated would it be to directly access the HW RNG (if present) that
> early in the boot?  It'd be nice if a U-Boot update weren't required (and
> particularly concerning that KASLR would appear to work without a U-Boot
> update, but without decent entropy).
>
> -Scott
>
>
>
> .