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Commit 85900ea5 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
Browse files

x86/pti: Map the vsyscall page if needed 



Make VSYSCALLs work fully in PTI mode by mapping them properly to the user
space visible page tables.

[ tglx: Hide unused functions (Patch by Arnd Bergmann) ]

Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent f55f0501

arch/x86/entry/vsyscall/vsyscall_64.c

+3 −3
Original line number Diff line number Diff line
@@ -344,14 +344,14 @@ int in_gate_area_no_mm(unsigned long addr) 
 * vsyscalls but leave the page not present.  If so, we skip calling

 * this.

 */

static void __init set_vsyscall_pgtable_user_bits(void)

void __init set_vsyscall_pgtable_user_bits(pgd_t *root)

{

	pgd_t *pgd;

	p4d_t *p4d;

	pud_t *pud;

	pmd_t *pmd;



	pgd = pgd_offset_k(VSYSCALL_ADDR);

	pgd = pgd_offset_pgd(root, VSYSCALL_ADDR);

	set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER));

	p4d = p4d_offset(pgd, VSYSCALL_ADDR);

#if CONFIG_PGTABLE_LEVELS >= 5
@@ -373,7 +373,7 @@ void __init map_vsyscall(void) 
			     vsyscall_mode == NATIVE

			     ? PAGE_KERNEL_VSYSCALL

			     : PAGE_KERNEL_VVAR);

		set_vsyscall_pgtable_user_bits();

		set_vsyscall_pgtable_user_bits(swapper_pg_dir);

	}



	BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=

arch/x86/include/asm/vsyscall.h

+1 −0
Original line number Diff line number Diff line
@@ -7,6 +7,7 @@ 


#ifdef CONFIG_X86_VSYSCALL_EMULATION

extern void map_vsyscall(void);

extern void set_vsyscall_pgtable_user_bits(pgd_t *root);



/*

 * Called on instruction fetch fault in vsyscall page.

arch/x86/mm/pti.c

+65 −0
Original line number Diff line number Diff line
@@ -38,6 +38,7 @@ 


#include <asm/cpufeature.h>

#include <asm/hypervisor.h>

#include <asm/vsyscall.h>

#include <asm/cmdline.h>

#include <asm/pti.h>

#include <asm/pgtable.h>
@@ -223,6 +224,69 @@ static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address) 
	return pmd_offset(pud, address);

}



#ifdef CONFIG_X86_VSYSCALL_EMULATION

/*

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

 * page table pages on the way down.  Does not support large pages.

 *

 * Note: this is only used when mapping *new* kernel data into the

 * user/shadow page tables.  It is never used for userspace data.

 *

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

 */

static __init pte_t *pti_user_pagetable_walk_pte(unsigned long address)

{

	gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);

	pmd_t *pmd = pti_user_pagetable_walk_pmd(address);

	pte_t *pte;



	/* We can't do anything sensible if we hit a large mapping. */

	if (pmd_large(*pmd)) {

		WARN_ON(1);

		return NULL;

	}



	if (pmd_none(*pmd)) {

		unsigned long new_pte_page = __get_free_page(gfp);

		if (!new_pte_page)

			return NULL;



		if (pmd_none(*pmd)) {

			set_pmd(pmd, __pmd(_KERNPG_TABLE | __pa(new_pte_page)));

			new_pte_page = 0;

		}

		if (new_pte_page)

			free_page(new_pte_page);

	}



	pte = pte_offset_kernel(pmd, address);

	if (pte_flags(*pte) & _PAGE_USER) {

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

		return NULL;

	}

	return pte;

}



static void __init pti_setup_vsyscall(void)

{

	pte_t *pte, *target_pte;

	unsigned int level;



	pte = lookup_address(VSYSCALL_ADDR, &level);

	if (!pte || WARN_ON(level != PG_LEVEL_4K) || pte_none(*pte))

		return;



	target_pte = pti_user_pagetable_walk_pte(VSYSCALL_ADDR);

	if (WARN_ON(!target_pte))

		return;



	*target_pte = *pte;

	set_vsyscall_pgtable_user_bits(kernel_to_user_pgdp(swapper_pg_dir));

}

#else

static void __init pti_setup_vsyscall(void) { }

#endif



static void __init

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

{
@@ -319,4 +383,5 @@ void __init pti_init(void) 
	pti_clone_user_shared();

	pti_clone_entry_text();

	pti_setup_espfix64();

	pti_setup_vsyscall();

}