Messages in this thread | | | Date | Fri, 24 Mar 2017 09:08:33 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH v2] x86/mm/KASLR: EFI region is mistakenly included into KASLR VA space for randomization |
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* Baoquan He <bhe@redhat.com> 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@vger.kernel.org> #4.8+ > Signed-off-by: Baoquan He <bhe@redhat.com> > Acked-by: Dave Young <dyoung@redhat.com> > Reviewed-by: Bhupesh Sharma <bhsharma@redhat.com> > Acked-by: Thomas Garnier <thgarnie@google.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: "H. Peter Anvin" <hpa@zytor.com> > Cc: x86@kernel.org > Cc: linux-efi@vger.kernel.org > Cc: Thomas Garnier <thgarnie@google.com> > Cc: Kees Cook <keescook@chromium.org> > Cc: Borislav Petkov <bp@alien8.de> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Masahiro Yamada <yamada.masahiro@socionext.com> > Cc: Dave Young <dyoung@redhat.com> > Cc: Bhupesh Sharma <bhsharma@redhat.com>
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
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