Re: [PATCH v2 RESEND 2/2] x86/mm/KASLR: Fix the size of vmemmap section

[Baoquan He]

On 04/15/19 at 09:47pm, Borislav Petkov wrote:
> On Sun, Apr 14, 2019 at 03:28:04PM +0800, Baoquan He wrote:
> > kernel_randomize_memory() hardcodes the size of vmemmap section as 1 TB,
> > to support the maximum amount of system RAM in 4-level paging mode, 64 TB.
> > 
> > However, 1 TB is not enough for vmemmap in 5-level paging mode. Assuming
> > the size of struct page is 64 Bytes, to support 4 PB system RAM in 5-level,
> > 64 TB of vmemmap area is needed. The wrong hardcoding may cause vmemmap
> > stamping into the following cpu_entry_area section, if KASLR puts vmemmap
> > very close to cpu_entry_area, and the actual area of vmemmap is much bigger
> > than 1 TB.
> > 
> > So here calculate the actual size of vmemmap region, then align up to 1 TB
> > boundary. In 4-level it's always 1 TB. In 5-level it's adjusted on demand.
> > The current code reserves 0.5 PB for vmemmap in 5-level. In this new methor,
> 								       ^^^^^^^
> 
> Please introduce a spellchecker into your patch creation workflow.

Sorry, forgot running checkpatch this time. Will update.

> 
> > the left space can be saved to join randomization to increase the entropy.
> > 
> > Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> > ---
> >  arch/x86/mm/kaslr.c | 11 ++++++++++-
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
> > index 387d4ed25d7c..4679a0075048 100644
> > --- a/arch/x86/mm/kaslr.c
> > +++ b/arch/x86/mm/kaslr.c
> > @@ -52,7 +52,7 @@ static __initdata struct kaslr_memory_region {
> >  } kaslr_regions[] = {
> >  	{ &page_offset_base, 0 },
> >  	{ &vmalloc_base, 0 },
> > -	{ &vmemmap_base, 1 },
> > +	{ &vmemmap_base, 0 },
> >  };
> >  
> >  /* Get size in bytes used by the memory region */
> > @@ -78,6 +78,7 @@ void __init kernel_randomize_memory(void)
> >  	unsigned long rand, memory_tb;
> >  	struct rnd_state rand_state;
> >  	unsigned long remain_entropy;
> > +	unsigned long vmemmap_size;
> >  
> >  	vaddr_start = pgtable_l5_enabled() ? __PAGE_OFFSET_BASE_L5 : __PAGE_OFFSET_BASE_L4;
> >  	vaddr = vaddr_start;
> > @@ -109,6 +110,14 @@ void __init kernel_randomize_memory(void)
> >  	if (memory_tb < kaslr_regions[0].size_tb)
> >  		kaslr_regions[0].size_tb = memory_tb;
> >  
> > +	/**
> > +	 * Calculate how many TB vmemmap region needs, and aligned to
> > +	 * 1TB boundary.
> > +	 */
> > +	vmemmap_size = (kaslr_regions[0].size_tb << (TB_SHIFT - PAGE_SHIFT)) *
> > +		sizeof(struct page);
> > +	kaslr_regions[2].size_tb = DIV_ROUND_UP(vmemmap_size, 1UL << TB_SHIFT);
> > +
> >  	/* Calculate entropy available between regions */
> >  	remain_entropy = vaddr_end - vaddr_start;
> >  	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)
> > -- 
> 
> Kirill, ack?
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> Good mailing practices for 400: avoid top-posting and trim the reply.