linux-kernel - Re: [RFC v1 3/4] x86, boot: Implement ASLR for kernel memory sections (x86

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Message-ID: <20160419142741.GI3886@suse.de>
Date:	Tue, 19 Apr 2016 16:27:41 +0200
From:	Joerg Roedel <jroedel@...e.de>
To:	Thomas Garnier <thgarnie@...gle.com>
Cc:	"H . Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...e.de>,
	Andy Lutomirski <luto@...nel.org>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Kees Cook <keescook@...omium.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Seth Jennings <sjennings@...iantweb.net>,
	Kefeng Wang <wangkefeng.wang@...wei.com>,
	Jonathan Corbet <corbet@....net>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Toshi Kani <toshi.kani@....com>,
	Alexander Kuleshov <kuleshovmail@...il.com>,
	Alexander Popov <alpopov@...ecurity.com>,
	Dave Young <dyoung@...hat.com>, Baoquan He <bhe@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Mark Salter <msalter@...hat.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	gthelen@...gle.com, kernel-hardening@...ts.openwall.com
Subject: Re: [RFC v1 3/4] x86, boot: Implement ASLR for kernel memory
 sections (x86_64)

Hi Thomas,

On Fri, Apr 15, 2016 at 03:03:12PM -0700, Thomas Garnier wrote:
> +/*
> + * Create PGD aligned trampoline table to allow real mode initialization
> + * of additional CPUs. Consume only 1 additonal low memory page.
> + */
> +void __meminit kaslr_trampoline_init(unsigned long page_size_mask)
> +{
> +	unsigned long addr, next, end;
> +	pgd_t *pgd;
> +	pud_t *pud_page, *tr_pud_page;
> +	int i;
> +
> +	if (!kaslr_enabled()) {
> +		trampoline_pgd_entry = init_level4_pgt[pgd_index(PAGE_OFFSET)];
> +		return;
> +	}
> +
> +	tr_pud_page = alloc_low_page();
> +	set_pgd(&trampoline_pgd_entry, __pgd(_PAGE_TABLE | __pa(tr_pud_page)));
> +
> +	addr = 0;
> +	end = ISA_END_ADDRESS;
> +	pgd = pgd_offset_k((unsigned long)__va(addr));
> +	pud_page = (pud_t *) pgd_page_vaddr(*pgd);
> +
> +	for (i = pud_index(addr); i < PTRS_PER_PUD; i++, addr = next) {
> +		pud_t *pud, *tr_pud;
> +		pmd_t *pmd;
> +
> +		tr_pud = tr_pud_page + pud_index(addr);
> +		pud = pud_page + pud_index((unsigned long)__va(addr));
> +		next = (addr & PUD_MASK) + PUD_SIZE;
> +
> +		if (addr >= end || !pud_val(*pud)) {
> +			if (!after_bootmem &&
> +			    !e820_any_mapped(addr & PUD_MASK, next, E820_RAM) &&
> +			    !e820_any_mapped(addr & PUD_MASK, next,
> +					    E820_RESERVED_KERN))
> +				set_pud(tr_pud, __pud(0));
> +			continue;
> +		}
> +
> +		if (page_size_mask & (1<<PG_LEVEL_1G)) {
> +			set_pte((pte_t *)tr_pud,
> +				pfn_pte((__pa(addr) & PUD_MASK) >> PAGE_SHIFT,

Hmm, why do you treat addr as virtual here, before it was a physical
address, no?

> +					PAGE_KERNEL_LARGE));
> +			continue;
> +		}

Why do you need to check these two cases above, can't you just copy the
pud-entries like done below? The direct mapping should already take care
of unmapped regions and 1gb pages.

> +		pmd = pmd_offset(pud, 0);
> +		set_pud(tr_pud, __pud(_PAGE_TABLE | __pa(pmd)));
> +	}
> +}


	Joerg