Re: [PATCH 2/2] x86/mm/KASLR: Correct the upper boundary of KALSR mm regions if adjacent to EFI
From: Baoquan He
Date: Wed Mar 15 2017 - 02:31:50 EST
On 03/15/17 at 02:13pm, Baoquan He wrote:
> PING!
>
> Is there any suggestion for this code bug fix?
>
> Boris added comment in patch 1/2 thread that it can also be fixed by
> swapping the naming - EFI_VA_START and EFI_VA_END. As he said the
> swapping can remove the confusion about the naming, while the con is
> changing it now could confuse more people who have the current
> mental picture of the mapping direction.
If swapping the naming is suggested, I can post v2 to change efi code.
Both of them is fine to me.
>
> And there's also a well known similar use case, stack, like stack_end
> naming in arch/x86/boot/main.c which is the low addr boundary of stack
> region.
>
> Any idea?
>
> Thanks
> Baoquan
>
> On 03/08/17 at 03:47pm, Baoquan He wrote:
> > EFI allocates runtime services regions top-down, starting from EFI_VA_START
> > to EFI_VA_END. So EFI_VA_START is bigger than EFI_VA_END and is the end of
> > EFI region. The upper boundary of memory regions randomized by KASLR should
> > be EFI_VA_END if it's adjacent to EFI region, but not EFI_VA_START.
> >
> > Correct it in this patch.
> >
> > Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> > ---
> > arch/x86/mm/kaslr.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
> > index 887e571..aed2064 100644
> > --- a/arch/x86/mm/kaslr.c
> > +++ b/arch/x86/mm/kaslr.c
> > @@ -48,7 +48,7 @@ static const unsigned long vaddr_start = __PAGE_OFFSET_BASE;
> > #if defined(CONFIG_X86_ESPFIX64)
> > static const unsigned long vaddr_end = ESPFIX_BASE_ADDR;
> > #elif defined(CONFIG_EFI)
> > -static const unsigned long vaddr_end = EFI_VA_START;
> > +static const unsigned long vaddr_end = EFI_VA_END;
> > #else
> > static const unsigned long vaddr_end = __START_KERNEL_map;
> > #endif
> > @@ -105,7 +105,7 @@ void __init kernel_randomize_memory(void)
> > */
> > BUILD_BUG_ON(vaddr_start >= vaddr_end);
> > BUILD_BUG_ON(IS_ENABLED(CONFIG_X86_ESPFIX64) &&
> > - vaddr_end >= EFI_VA_START);
> > + vaddr_end >= EFI_VA_END);
> > BUILD_BUG_ON((IS_ENABLED(CONFIG_X86_ESPFIX64) ||
> > IS_ENABLED(CONFIG_EFI)) &&
> > vaddr_end >= __START_KERNEL_map);
> > --
> > 2.5.5
> >