Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into KASLR VA space for randomization

[Ingo Molnar]

* Baoquan He <bhe@xxxxxxxxxx> wrote:

> Currently KASLR is enabled on three regions: the direct mapping of physical
> memory, vamlloc and vmemmap. However EFI region is also mistakenly included
> for VA space randomization because of misusing EFI_VA_START macro and
> assuming EFI_VA_START < EFI_VA_END.
> 
> The EFI region is reserved for EFI runtime services virtual mapping which
> should not be included in kaslr ranges. In Documentation/x86/x86_64/mm.txt,
> we can see:
>   ffffffef00000000 - fffffffeffffffff (=64 GB) EFI region mapping space
> EFI use the space from -4G to -64G thus EFI_VA_START > EFI_VA_END,
> Here EFI_VA_START = -4G, and EFI_VA_END = -64G.
> 
> Changing EFI_VA_START to EFI_VA_END in mm/kaslr.c fixes this problem.
> 
> Cc: <stable@xxxxxxxxxxxxxxx> #4.8+
> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> Acked-by: Dave Young <dyoung@xxxxxxxxxx>
> Reviewed-by: Bhupesh Sharma <bhsharma@xxxxxxxxxx>
> Acked-by: Thomas Garnier <thgarnie@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: linux-efi@xxxxxxxxxxxxxxx
> Cc: Thomas Garnier <thgarnie@xxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> Cc: Dave Young <dyoung@xxxxxxxxxx>
> Cc: Bhupesh Sharma <bhsharma@xxxxxxxxxx>

So I applied this kexec fix and extended the changelog to clearly show why this 
fix matters in practice.

Also, to make sure I understood it correctly: these addresses are all dynamic on 
64-bit kernels, i.e. we are establishing and then tearing down these page tables 
around EFI calls, and they are 'normally' not present at all, right?

Thanks,

	Ingo