arch/x86/kernel/espfix_64.c - linux - Git at Google

 /* ----------------------------------------------------------------------- *
  *
  *   Copyright 2014 Intel Corporation; author: H. Peter Anvin
  *
  *   This program is free software; you can redistribute it and/or modify it
  *   under the terms and conditions of the GNU General Public License,
  *   version 2, as published by the Free Software Foundation.
  *
  *   This program is distributed in the hope it will be useful, but WITHOUT
  *   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  *   FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  *   more details.
  *
  * ----------------------------------------------------------------------- */

 /*
  * The IRET instruction, when returning to a 16-bit segment, only
  * restores the bottom 16 bits of the user space stack pointer.  This
  * causes some 16-bit software to break, but it also leaks kernel state
  * to user space.
  *
  * This works around this by creating percpu "ministacks", each of which
  * is mapped 2^16 times 64K apart.  When we detect that the return SS is
  * on the LDT, we copy the IRET frame to the ministack and use the
  * relevant alias to return to userspace.  The ministacks are mapped
  * readonly, so if the IRET fault we promote #GP to #DF which is an IST
  * vector and thus has its own stack; we then do the fixup in the #DF
  * handler.
  *
  * This file sets up the ministacks and the related page tables.  The
  * actual ministack invocation is in entry_64.S.
  */

 #include <linux/init.h>
 #include <linux/init_task.h>
 #include <linux/kernel.h>
 #include <linux/percpu.h>
 #include <linux/gfp.h>
 #include <linux/random.h>
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
 #include <asm/setup.h>
 #include <asm/espfix.h>

 /*
  * Note: we only need 6*8 = 48 bytes for the espfix stack, but round
  * it up to a cache line to avoid unnecessary sharing.
  */
 #define ESPFIX_STACK_SIZE	(8*8UL)
 #define ESPFIX_STACKS_PER_PAGE	(PAGE_SIZE/ESPFIX_STACK_SIZE)

 /* There is address space for how many espfix pages? */
 #define ESPFIX_PAGE_SPACE	(1UL << (P4D_SHIFT-PAGE_SHIFT-16))

 #define ESPFIX_MAX_CPUS		(ESPFIX_STACKS_PER_PAGE * ESPFIX_PAGE_SPACE)
 #if CONFIG_NR_CPUS > ESPFIX_MAX_CPUS
 # error "Need more virtual address space for the ESPFIX hack"
 #endif

 #define PGALLOC_GFP (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO)

 /* This contains the *bottom* address of the espfix stack */
 DEFINE_PER_CPU_READ_MOSTLY(unsigned long, espfix_stack);
 DEFINE_PER_CPU_READ_MOSTLY(unsigned long, espfix_waddr);

 /* Initialization mutex - should this be a spinlock? */
 static DEFINE_MUTEX(espfix_init_mutex);

 /* Page allocation bitmap - each page serves ESPFIX_STACKS_PER_PAGE CPUs */
 #define ESPFIX_MAX_PAGES  DIV_ROUND_UP(CONFIG_NR_CPUS, ESPFIX_STACKS_PER_PAGE)
 static void *espfix_pages[ESPFIX_MAX_PAGES];

 static __page_aligned_bss pud_t espfix_pud_page[PTRS_PER_PUD]
 	__aligned(PAGE_SIZE);

 static unsigned int page_random, slot_random;

 /*
  * This returns the bottom address of the espfix stack for a specific CPU.
  * The math allows for a non-power-of-two ESPFIX_STACK_SIZE, in which case
  * we have to account for some amount of padding at the end of each page.
  */
 static inline unsigned long espfix_base_addr(unsigned int cpu)
 {
 	unsigned long page, slot;
 	unsigned long addr;

 	page = (cpu / ESPFIX_STACKS_PER_PAGE) ^ page_random;
 	slot = (cpu + slot_random) % ESPFIX_STACKS_PER_PAGE;
 	addr = (page << PAGE_SHIFT) + (slot * ESPFIX_STACK_SIZE);
 	addr = (addr & 0xffffUL) | ((addr & ~0xffffUL) << 16);
 	addr += ESPFIX_BASE_ADDR;
 	return addr;
 }

 #define PTE_STRIDE        (65536/PAGE_SIZE)
 #define ESPFIX_PTE_CLONES (PTRS_PER_PTE/PTE_STRIDE)
 #define ESPFIX_PMD_CLONES PTRS_PER_PMD
 #define ESPFIX_PUD_CLONES (65536/(ESPFIX_PTE_CLONES*ESPFIX_PMD_CLONES))

 #define PGTABLE_PROT	  ((_KERNPG_TABLE & ~_PAGE_RW) | _PAGE_NX)

 static void init_espfix_random(void)
 {
 	unsigned long rand;

 	/*
 	 * This is run before the entropy pools are initialized,
 	 * but this is hopefully better than nothing.
 	 */
 	if (!arch_get_random_long(&rand)) {
 		/* The constant is an arbitrary large prime */
 		rand = rdtsc();
 		rand *= 0xc345c6b72fd16123UL;
 	}

 	slot_random = rand % ESPFIX_STACKS_PER_PAGE;
 	page_random = (rand / ESPFIX_STACKS_PER_PAGE)
 		& (ESPFIX_PAGE_SPACE - 1);
 }

 void __init init_espfix_bsp(void)
 {
 	pgd_t *pgd;
 	p4d_t *p4d;

 	/* Install the espfix pud into the kernel page directory */
 	pgd = &init_top_pgt[pgd_index(ESPFIX_BASE_ADDR)];
 	p4d = p4d_alloc(&init_mm, pgd, ESPFIX_BASE_ADDR);
 	p4d_populate(&init_mm, p4d, espfix_pud_page);

 	/* Randomize the locations */
 	init_espfix_random();

 	/* The rest is the same as for any other processor */
 	init_espfix_ap(0);
 }

 void init_espfix_ap(int cpu)
 {
 	unsigned int page;
 	unsigned long addr;
 	pud_t pud, *pud_p;
 	pmd_t pmd, *pmd_p;
 	pte_t pte, *pte_p;
 	int n, node;
 	void *stack_page;
 	pteval_t ptemask;

 	/* We only have to do this once... */
 	if (likely(per_cpu(espfix_stack, cpu)))
 		return;		/* Already initialized */

 	addr = espfix_base_addr(cpu);
 	page = cpu/ESPFIX_STACKS_PER_PAGE;

 	/* Did another CPU already set this up? */
 	stack_page = ACCESS_ONCE(espfix_pages[page]);
 	if (likely(stack_page))
 		goto done;

 	mutex_lock(&espfix_init_mutex);

 	/* Did we race on the lock? */
 	stack_page = ACCESS_ONCE(espfix_pages[page]);
 	if (stack_page)
 		goto unlock_done;

 	node = cpu_to_node(cpu);
 	ptemask = __supported_pte_mask;

 	pud_p = &espfix_pud_page[pud_index(addr)];
 	pud = *pud_p;
 	if (!pud_present(pud)) {
 		struct page *page = alloc_pages_node(node, PGALLOC_GFP, 0);

 		pmd_p = (pmd_t *)page_address(page);
 		pud = __pud(__pa(pmd_p) | (PGTABLE_PROT & ptemask));
 		paravirt_alloc_pmd(&init_mm, __pa(pmd_p) >> PAGE_SHIFT);
 		for (n = 0; n < ESPFIX_PUD_CLONES; n++)
 			set_pud(&pud_p[n], pud);
 	}

 	pmd_p = pmd_offset(&pud, addr);
 	pmd = *pmd_p;
 	if (!pmd_present(pmd)) {
 		struct page *page = alloc_pages_node(node, PGALLOC_GFP, 0);

 		pte_p = (pte_t *)page_address(page);
 		pmd = __pmd(__pa(pte_p) | (PGTABLE_PROT & ptemask));
 		paravirt_alloc_pte(&init_mm, __pa(pte_p) >> PAGE_SHIFT);
 		for (n = 0; n < ESPFIX_PMD_CLONES; n++)
 			set_pmd(&pmd_p[n], pmd);
 	}

 	pte_p = pte_offset_kernel(&pmd, addr);
 	stack_page = page_address(alloc_pages_node(node, GFP_KERNEL, 0));
 	pte = __pte(__pa(stack_page) | (__PAGE_KERNEL_RO & ptemask));
 	for (n = 0; n < ESPFIX_PTE_CLONES; n++)
 		set_pte(&pte_p[n*PTE_STRIDE], pte);

 	/* Job is done for this CPU and any CPU which shares this page */
 	ACCESS_ONCE(espfix_pages[page]) = stack_page;

 unlock_done:
 	mutex_unlock(&espfix_init_mutex);
 done:
 	per_cpu(espfix_stack, cpu) = addr;
 	per_cpu(espfix_waddr, cpu) = (unsigned long)stack_page
 				      + (addr & ~PAGE_MASK);
 }
	/* ----------------------------------------------------------------------- *
	*
	* Copyright 2014 Intel Corporation; author: H. Peter Anvin
	*
	* This program is free software; you can redistribute it and/or modify it
	* under the terms and conditions of the GNU General Public License,
	* version 2, as published by the Free Software Foundation.
	*
	* This program is distributed in the hope it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
	* more details.
	*
	* ----------------------------------------------------------------------- */

	/*
	* The IRET instruction, when returning to a 16-bit segment, only
	* restores the bottom 16 bits of the user space stack pointer. This
	* causes some 16-bit software to break, but it also leaks kernel state
	* to user space.
	*
	* This works around this by creating percpu "ministacks", each of which
	* is mapped 2^16 times 64K apart. When we detect that the return SS is
	* on the LDT, we copy the IRET frame to the ministack and use the
	* relevant alias to return to userspace. The ministacks are mapped
	* readonly, so if the IRET fault we promote #GP to #DF which is an IST
	* vector and thus has its own stack; we then do the fixup in the #DF
	* handler.
	*
	* This file sets up the ministacks and the related page tables. The
	* actual ministack invocation is in entry_64.S.
	*/

	#include <linux/init.h>
	#include <linux/init_task.h>
	#include <linux/kernel.h>
	#include <linux/percpu.h>
	#include <linux/gfp.h>
	#include <linux/random.h>
	#include <asm/pgtable.h>
	#include <asm/pgalloc.h>
	#include <asm/setup.h>
	#include <asm/espfix.h>

	/*
	* Note: we only need 6*8 = 48 bytes for the espfix stack, but round
	* it up to a cache line to avoid unnecessary sharing.
	*/
	#define ESPFIX_STACK_SIZE (8*8UL)
	#define ESPFIX_STACKS_PER_PAGE (PAGE_SIZE/ESPFIX_STACK_SIZE)

	/* There is address space for how many espfix pages? */
	#define ESPFIX_PAGE_SPACE (1UL << (P4D_SHIFT-PAGE_SHIFT-16))

	#define ESPFIX_MAX_CPUS (ESPFIX_STACKS_PER_PAGE * ESPFIX_PAGE_SPACE)
	#if CONFIG_NR_CPUS > ESPFIX_MAX_CPUS
	# error "Need more virtual address space for the ESPFIX hack"
	#endif

	#define PGALLOC_GFP (GFP_KERNEL \| __GFP_NOTRACK \| __GFP_ZERO)

	/* This contains the bottom address of the espfix stack */
	DEFINE_PER_CPU_READ_MOSTLY(unsigned long, espfix_stack);
	DEFINE_PER_CPU_READ_MOSTLY(unsigned long, espfix_waddr);

	/* Initialization mutex - should this be a spinlock? */
	static DEFINE_MUTEX(espfix_init_mutex);

	/* Page allocation bitmap - each page serves ESPFIX_STACKS_PER_PAGE CPUs */
	#define ESPFIX_MAX_PAGES DIV_ROUND_UP(CONFIG_NR_CPUS, ESPFIX_STACKS_PER_PAGE)
	static void *espfix_pages[ESPFIX_MAX_PAGES];

	static __page_aligned_bss pud_t espfix_pud_page[PTRS_PER_PUD]
	__aligned(PAGE_SIZE);

	static unsigned int page_random, slot_random;

	/*
	* This returns the bottom address of the espfix stack for a specific CPU.
	* The math allows for a non-power-of-two ESPFIX_STACK_SIZE, in which case
	* we have to account for some amount of padding at the end of each page.
	*/
	static inline unsigned long espfix_base_addr(unsigned int cpu)
	{
	unsigned long page, slot;
	unsigned long addr;

	page = (cpu / ESPFIX_STACKS_PER_PAGE) ^ page_random;
	slot = (cpu + slot_random) % ESPFIX_STACKS_PER_PAGE;
	addr = (page << PAGE_SHIFT) + (slot * ESPFIX_STACK_SIZE);
	addr = (addr & 0xffffUL) \| ((addr & ~0xffffUL) << 16);
	addr += ESPFIX_BASE_ADDR;
	return addr;
	}

	#define PTE_STRIDE (65536/PAGE_SIZE)
	#define ESPFIX_PTE_CLONES (PTRS_PER_PTE/PTE_STRIDE)
	#define ESPFIX_PMD_CLONES PTRS_PER_PMD
	#define ESPFIX_PUD_CLONES (65536/(ESPFIX_PTE_CLONES*ESPFIX_PMD_CLONES))

	#define PGTABLE_PROT ((_KERNPG_TABLE & ~_PAGE_RW) \| _PAGE_NX)

	static void init_espfix_random(void)
	{
	unsigned long rand;

	/*
	* This is run before the entropy pools are initialized,
	* but this is hopefully better than nothing.
	*/
	if (!arch_get_random_long(&rand)) {
	/* The constant is an arbitrary large prime */
	rand = rdtsc();
	rand *= 0xc345c6b72fd16123UL;
	}

	slot_random = rand % ESPFIX_STACKS_PER_PAGE;
	page_random = (rand / ESPFIX_STACKS_PER_PAGE)
	& (ESPFIX_PAGE_SPACE - 1);
	}

	void __init init_espfix_bsp(void)
	{
	pgd_t *pgd;
	p4d_t *p4d;

	/* Install the espfix pud into the kernel page directory */
	pgd = &init_top_pgt[pgd_index(ESPFIX_BASE_ADDR)];
	p4d = p4d_alloc(&init_mm, pgd, ESPFIX_BASE_ADDR);
	p4d_populate(&init_mm, p4d, espfix_pud_page);

	/* Randomize the locations */
	init_espfix_random();

	/* The rest is the same as for any other processor */
	init_espfix_ap(0);
	}

	void init_espfix_ap(int cpu)
	{
	unsigned int page;
	unsigned long addr;
	pud_t pud, *pud_p;
	pmd_t pmd, *pmd_p;
	pte_t pte, *pte_p;
	int n, node;
	void *stack_page;
	pteval_t ptemask;

	/* We only have to do this once... */
	if (likely(per_cpu(espfix_stack, cpu)))
	return; /* Already initialized */

	addr = espfix_base_addr(cpu);
	page = cpu/ESPFIX_STACKS_PER_PAGE;

	/* Did another CPU already set this up? */
	stack_page = ACCESS_ONCE(espfix_pages[page]);
	if (likely(stack_page))
	goto done;

	mutex_lock(&espfix_init_mutex);

	/* Did we race on the lock? */
	stack_page = ACCESS_ONCE(espfix_pages[page]);
	if (stack_page)
	goto unlock_done;

	node = cpu_to_node(cpu);
	ptemask = __supported_pte_mask;

	pud_p = &espfix_pud_page[pud_index(addr)];
	pud = *pud_p;
	if (!pud_present(pud)) {
	struct page *page = alloc_pages_node(node, PGALLOC_GFP, 0);

	pmd_p = (pmd_t *)page_address(page);
	pud = __pud(__pa(pmd_p) \| (PGTABLE_PROT & ptemask));
	paravirt_alloc_pmd(&init_mm, __pa(pmd_p) >> PAGE_SHIFT);
	for (n = 0; n < ESPFIX_PUD_CLONES; n++)
	set_pud(&pud_p[n], pud);
	}

	pmd_p = pmd_offset(&pud, addr);
	pmd = *pmd_p;
	if (!pmd_present(pmd)) {
	struct page *page = alloc_pages_node(node, PGALLOC_GFP, 0);

	pte_p = (pte_t *)page_address(page);
	pmd = __pmd(__pa(pte_p) \| (PGTABLE_PROT & ptemask));
	paravirt_alloc_pte(&init_mm, __pa(pte_p) >> PAGE_SHIFT);
	for (n = 0; n < ESPFIX_PMD_CLONES; n++)
	set_pmd(&pmd_p[n], pmd);
	}

	pte_p = pte_offset_kernel(&pmd, addr);
	stack_page = page_address(alloc_pages_node(node, GFP_KERNEL, 0));
	pte = __pte(__pa(stack_page) \| (__PAGE_KERNEL_RO & ptemask));
	for (n = 0; n < ESPFIX_PTE_CLONES; n++)
	set_pte(&pte_p[n*PTE_STRIDE], pte);

	/* Job is done for this CPU and any CPU which shares this page */
	ACCESS_ONCE(espfix_pages[page]) = stack_page;

	unlock_done:
	mutex_unlock(&espfix_init_mutex);
	done:
	per_cpu(espfix_stack, cpu) = addr;
	per_cpu(espfix_waddr, cpu) = (unsigned long)stack_page
	+ (addr & ~PAGE_MASK);
	}