linux-kernel - Re: [PATCH 2/2] x86/mm/KASLR: Correct the upper boundary of KALSR mm regions if adjacent to EFI

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Date:   Wed, 15 Mar 2017 14:31:42 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-efi@...r.kernel.org, thgarnie@...gle.com,
        keescook@...omium.org, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, x86@...nel.org, bp@...e.de, dyoung@...hat.com
Subject: Re: [PATCH 2/2] x86/mm/KASLR: Correct the upper boundary of KALSR mm
 regions if adjacent to EFI

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@...hat.com>
> > ---
> >  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
> >