Re: [PATCH] x86/boot/64: Fix crash if kernel images crosses page table boundary

[Thomas Gleixner]

On Tue, 25 Jun 2019, Thomas Gleixner wrote:

> On Tue, 25 Jun 2019, Kirill A. Shutemov wrote:
> > On Tue, Jun 25, 2019 at 09:04:39PM +0200, Thomas Gleixner wrote:
> > 
> > > > +		pmd[idx % PTRS_PER_PMD] = pmd_entry + i * PMD_SIZE;
> > > 
> > > This part is functionally equivivalent. So what's the value of this change?
> > 
> > Precedence of operators were broken
> > 
> > 	idx =  i + (physaddr >> PMD_SHIFT) % PTRS_PER_PMD;
> > 
> > reads by compiler as
> > 
> > 	idx = i + ((physaddr >> PMD_SHIFT) % PTRS_PER_PMD);
> > 
> > not as
> > 
> > 	idx =  (i + (physaddr >> PMD_SHIFT)) % PTRS_PER_PMD;
> > 
> > Therefore 'idx' can become >= PTRS_PER_PMD.
> 
> Indeed. Please mention it in the change log. I did not spot it right away.

I fixed it up already. No need to resend.

Thanks,

	tglx