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Commit 577eebea authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge
Browse files

xen: make -fstack-protector work under Xen 



-fstack-protector uses a special per-cpu "stack canary" value.
gcc generates special code in each function to test the canary to make
sure that the function's stack hasn't been overrun.

On x86-64, this is simply an offset of %gs, which is the usual per-cpu
base segment register, so setting it up simply requires loading %gs's
base as normal.

On i386, the stack protector segment is %gs (rather than the usual kernel
percpu %fs segment register).  This requires setting up the full kernel
GDT and then loading %gs accordingly.  We also need to make sure %gs is
initialized when bringing up secondary cpus too.

To keep things consistent, we do the full GDT/segment register setup on
both architectures.

Because we need to avoid -fstack-protected code before setting up the GDT
and because there's no way to disable it on a per-function basis, several
files need to have stack-protector inhibited.

[ Impact: allow Xen booting with stack-protector enabled ]

Signed-off-by: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
parent e07cccf4

arch/x86/mm/Makefile

+4 −0
Original line number Diff line number Diff line 
obj-y	:=  init.o init_$(BITS).o fault.o ioremap.o extable.o pageattr.o mmap.o \

	    pat.o pgtable.o gup.o



# Make sure __phys_addr has no stackprotector

nostackp := $(call cc-option, -fno-stack-protector)

CFLAGS_ioremap.o		:= $(nostackp)



obj-$(CONFIG_SMP)		+= tlb.o



obj-$(CONFIG_X86_32)		+= pgtable_32.o iomap_32.o

arch/x86/xen/Makefile

+2 −0
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ endif 
# Make sure early boot has no stackprotector

nostackp := $(call cc-option, -fno-stack-protector)

CFLAGS_enlighten.o		:= $(nostackp)

CFLAGS_mmu.o			:= $(nostackp)



obj-y		:= enlighten.o setup.o multicalls.o mmu.o irq.o \

			time.o xen-asm.o xen-asm_$(BITS).o \
@@ -16,3 +17,4 @@ obj-y := enlighten.o setup.o multicalls.o mmu.o irq.o \ 
obj-$(CONFIG_SMP)		+= smp.o

obj-$(CONFIG_PARAVIRT_SPINLOCKS)+= spinlock.o

obj-$(CONFIG_XEN_DEBUG_FS)	+= debugfs.o

arch/x86/xen/enlighten.c

+112 −19
Original line number Diff line number Diff line
@@ -51,6 +51,7 @@ 
#include <asm/pgtable.h>

#include <asm/tlbflush.h>

#include <asm/reboot.h>

#include <asm/stackprotector.h>



#include "xen-ops.h"

#include "mmu.h"
@@ -330,18 +331,28 @@ static void xen_load_gdt(const struct desc_ptr *dtr) 
	unsigned long frames[pages];

	int f;



	/* A GDT can be up to 64k in size, which corresponds to 8192

	   8-byte entries, or 16 4k pages.. */

	/*

	 * A GDT can be up to 64k in size, which corresponds to 8192

	 * 8-byte entries, or 16 4k pages..

	 */



	BUG_ON(size > 65536);

	BUG_ON(va & ~PAGE_MASK);



	for (f = 0; va < dtr->address + size; va += PAGE_SIZE, f++) {

		int level;

		pte_t *ptep = lookup_address(va, &level);

		pte_t *ptep;

		unsigned long pfn, mfn;

		void *virt;



		/*

		 * The GDT is per-cpu and is in the percpu data area.

		 * That can be virtually mapped, so we need to do a

		 * page-walk to get the underlying MFN for the

		 * hypercall.  The page can also be in the kernel's

		 * linear range, so we need to RO that mapping too.

		 */

		ptep = lookup_address(va, &level);

		BUG_ON(ptep == NULL);



		pfn = pte_pfn(*ptep);
@@ -358,6 +369,44 @@ static void xen_load_gdt(const struct desc_ptr *dtr) 
		BUG();

}



/*

 * load_gdt for early boot, when the gdt is only mapped once

 */

static __init void xen_load_gdt_boot(const struct desc_ptr *dtr)

{

	unsigned long va = dtr->address;

	unsigned int size = dtr->size + 1;

	unsigned pages = (size + PAGE_SIZE - 1) / PAGE_SIZE;

	unsigned long frames[pages];

	int f;



	/*

	 * A GDT can be up to 64k in size, which corresponds to 8192

	 * 8-byte entries, or 16 4k pages..

	 */



	BUG_ON(size > 65536);

	BUG_ON(va & ~PAGE_MASK);



	for (f = 0; va < dtr->address + size; va += PAGE_SIZE, f++) {

		pte_t pte;

		unsigned long pfn, mfn;



		pfn = virt_to_pfn(va);

		mfn = pfn_to_mfn(pfn);



		pte = pfn_pte(pfn, PAGE_KERNEL_RO);



		if (HYPERVISOR_update_va_mapping((unsigned long)va, pte, 0))

			BUG();



		frames[f] = mfn;

	}



	if (HYPERVISOR_set_gdt(frames, size / sizeof(struct desc_struct)))

		BUG();

}



static void load_TLS_descriptor(struct thread_struct *t,

				unsigned int cpu, unsigned int i)

{
@@ -581,6 +630,29 @@ static void xen_write_gdt_entry(struct desc_struct *dt, int entry, 
	preempt_enable();

}



/*

 * Version of write_gdt_entry for use at early boot-time needed to

 * update an entry as simply as possible.

 */

static __init void xen_write_gdt_entry_boot(struct desc_struct *dt, int entry,

					    const void *desc, int type)

{

	switch (type) {

	case DESC_LDT:

	case DESC_TSS:

		/* ignore */

		break;



	default: {

		xmaddr_t maddr = virt_to_machine(&dt[entry]);



		if (HYPERVISOR_update_descriptor(maddr.maddr, *(u64 *)desc))

			dt[entry] = *(struct desc_struct *)desc;

	}



	}

}



static void xen_load_sp0(struct tss_struct *tss,

			 struct thread_struct *thread)

{
@@ -965,6 +1037,23 @@ static const struct machine_ops __initdata xen_machine_ops = { 
	.emergency_restart = xen_emergency_restart,

};



/*

 * Set up the GDT and segment registers for -fstack-protector.  Until

 * we do this, we have to be careful not to call any stack-protected

 * function, which is most of the kernel.

 */

static void __init xen_setup_stackprotector(void)

{

	pv_cpu_ops.write_gdt_entry = xen_write_gdt_entry_boot;

	pv_cpu_ops.load_gdt = xen_load_gdt_boot;



	setup_stack_canary_segment(0);

	switch_to_new_gdt(0);



	pv_cpu_ops.write_gdt_entry = xen_write_gdt_entry;

	pv_cpu_ops.load_gdt = xen_load_gdt;

}



/* First C function to be called on Xen boot */

asmlinkage void __init xen_start_kernel(void)

{
@@ -983,13 +1072,28 @@ asmlinkage void __init xen_start_kernel(void) 
	pv_apic_ops = xen_apic_ops;

	pv_mmu_ops = xen_mmu_ops;



#ifdef CONFIG_X86_64

	/*

	 * Setup percpu state.  We only need to do this for 64-bit

	 * because 32-bit already has %fs set properly.

	 * Set up some pagetable state before starting to set any ptes.

	 */

	load_percpu_segment(0);

#endif



	/* Prevent unwanted bits from being set in PTEs. */

	__supported_pte_mask &= ~_PAGE_GLOBAL;

	if (!xen_initial_domain())

		__supported_pte_mask &= ~(_PAGE_PWT | _PAGE_PCD);



	__supported_pte_mask |= _PAGE_IOMAP;



	xen_setup_features();



	/* Get mfn list */

	if (!xen_feature(XENFEAT_auto_translated_physmap))

		xen_build_dynamic_phys_to_machine();



	/*

	 * Set up kernel GDT and segment registers, mainly so that

	 * -fstack-protector code can be executed.

	 */

	xen_setup_stackprotector();



	xen_init_irq_ops();

	xen_init_cpuid_mask();
@@ -1001,8 +1105,6 @@ asmlinkage void __init xen_start_kernel(void) 
	set_xen_basic_apic_ops();

#endif



	xen_setup_features();



	if (xen_feature(XENFEAT_mmu_pt_update_preserve_ad)) {

		pv_mmu_ops.ptep_modify_prot_start = xen_ptep_modify_prot_start;

		pv_mmu_ops.ptep_modify_prot_commit = xen_ptep_modify_prot_commit;
@@ -1019,17 +1121,8 @@ asmlinkage void __init xen_start_kernel(void) 


	xen_smp_init();



	/* Get mfn list */

	if (!xen_feature(XENFEAT_auto_translated_physmap))

		xen_build_dynamic_phys_to_machine();



	pgd = (pgd_t *)xen_start_info->pt_base;



	/* Prevent unwanted bits from being set in PTEs. */

	__supported_pte_mask &= ~_PAGE_GLOBAL;

	if (!xen_initial_domain())

		__supported_pte_mask &= ~(_PAGE_PWT | _PAGE_PCD);



#ifdef CONFIG_X86_64

	/* Work out if we support NX */

	check_efer();

arch/x86/xen/smp.c

+1 −0
Original line number Diff line number Diff line
@@ -236,6 +236,7 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle) 
	ctxt->user_regs.ss = __KERNEL_DS;

#ifdef CONFIG_X86_32

	ctxt->user_regs.fs = __KERNEL_PERCPU;

	ctxt->user_regs.gs = __KERNEL_STACK_CANARY;

#else

	ctxt->gs_base_kernel = per_cpu_offset(cpu);

#endif

drivers/xen/Makefile

+3 −0
Original line number Diff line number Diff line 
obj-y	+= grant-table.o features.o events.o manage.o

obj-y	+= xenbus/



nostackp := $(call cc-option, -fno-stack-protector)

CFLAGS_features.o			:= $(nostackp)



obj-$(CONFIG_HOTPLUG_CPU)	+= cpu_hotplug.o

obj-$(CONFIG_XEN_XENCOMM)	+= xencomm.o

obj-$(CONFIG_XEN_BALLOON)	+= balloon.o