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Commit 03f4424f authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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x86/mm/pti: Add functions to clone kernel PMDs 



Provide infrastructure to:

 - find a kernel PMD for a mapping which must be visible to user space for
   the entry/exit code to work.

 - walk an address range and share the kernel PMD with it.

This reuses a small part of the original KAISER patches to populate the
user space page table.

[ tglx: Made it universally usable so it can be used for any kind of shared
	mapping. Add a mechanism to clear specific bits in the user space
	visible PMD entry. Folded Andys simplifactions ]

Originally-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent fc2fbc85

arch/x86/mm/pti.c

+127 −0
Original line number Diff line number Diff line
@@ -48,6 +48,11 @@ 
#undef pr_fmt

#define pr_fmt(fmt)     "Kernel/User page tables isolation: " fmt



/* Backporting helper */

#ifndef __GFP_NOTRACK

#define __GFP_NOTRACK	0

#endif



static void __init pti_print_if_insecure(const char *reason)

{

	if (boot_cpu_has_bug(X86_BUG_CPU_INSECURE))
@@ -137,6 +142,128 @@ pgd_t __pti_set_user_pgd(pgd_t *pgdp, pgd_t pgd) 
	return pgd;

}



/*

 * Walk the user copy of the page tables (optionally) trying to allocate

 * page table pages on the way down.

 *

 * Returns a pointer to a P4D on success, or NULL on failure.

 */

static p4d_t *pti_user_pagetable_walk_p4d(unsigned long address)

{

	pgd_t *pgd = kernel_to_user_pgdp(pgd_offset_k(address));

	gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);



	if (address < PAGE_OFFSET) {

		WARN_ONCE(1, "attempt to walk user address\n");

		return NULL;

	}



	if (pgd_none(*pgd)) {

		unsigned long new_p4d_page = __get_free_page(gfp);

		if (!new_p4d_page)

			return NULL;



		if (pgd_none(*pgd)) {

			set_pgd(pgd, __pgd(_KERNPG_TABLE | __pa(new_p4d_page)));

			new_p4d_page = 0;

		}

		if (new_p4d_page)

			free_page(new_p4d_page);

	}

	BUILD_BUG_ON(pgd_large(*pgd) != 0);



	return p4d_offset(pgd, address);

}



/*

 * Walk the user copy of the page tables (optionally) trying to allocate

 * page table pages on the way down.

 *

 * Returns a pointer to a PMD on success, or NULL on failure.

 */

static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)

{

	gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);

	p4d_t *p4d = pti_user_pagetable_walk_p4d(address);

	pud_t *pud;



	BUILD_BUG_ON(p4d_large(*p4d) != 0);

	if (p4d_none(*p4d)) {

		unsigned long new_pud_page = __get_free_page(gfp);

		if (!new_pud_page)

			return NULL;



		if (p4d_none(*p4d)) {

			set_p4d(p4d, __p4d(_KERNPG_TABLE | __pa(new_pud_page)));

			new_pud_page = 0;

		}

		if (new_pud_page)

			free_page(new_pud_page);

	}



	pud = pud_offset(p4d, address);

	/* The user page tables do not use large mappings: */

	if (pud_large(*pud)) {

		WARN_ON(1);

		return NULL;

	}

	if (pud_none(*pud)) {

		unsigned long new_pmd_page = __get_free_page(gfp);

		if (!new_pmd_page)

			return NULL;



		if (pud_none(*pud)) {

			set_pud(pud, __pud(_KERNPG_TABLE | __pa(new_pmd_page)));

			new_pmd_page = 0;

		}

		if (new_pmd_page)

			free_page(new_pmd_page);

	}



	return pmd_offset(pud, address);

}



static void __init

pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear)

{

	unsigned long addr;



	/*

	 * Clone the populated PMDs which cover start to end. These PMD areas

	 * can have holes.

	 */

	for (addr = start; addr < end; addr += PMD_SIZE) {

		pmd_t *pmd, *target_pmd;

		pgd_t *pgd;

		p4d_t *p4d;

		pud_t *pud;



		pgd = pgd_offset_k(addr);

		if (WARN_ON(pgd_none(*pgd)))

			return;

		p4d = p4d_offset(pgd, addr);

		if (WARN_ON(p4d_none(*p4d)))

			return;

		pud = pud_offset(p4d, addr);

		if (pud_none(*pud))

			continue;

		pmd = pmd_offset(pud, addr);

		if (pmd_none(*pmd))

			continue;



		target_pmd = pti_user_pagetable_walk_pmd(addr);

		if (WARN_ON(!target_pmd))

			return;



		/*

		 * Copy the PMD.  That is, the kernelmode and usermode

		 * tables will share the last-level page tables of this

		 * address range

		 */

		*target_pmd = pmd_clear_flags(*pmd, clear);

	}

}



/*

 * Initialize kernel page table isolation

 */