From 577eebeae34d340685d8985dfdb7dfe337c511e8 Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Thu, 27 Aug 2009 12:46:35 -0700 Subject: 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: Jeremy Fitzhardinge --- arch/x86/xen/Makefile | 2 + arch/x86/xen/enlighten.c | 131 ++++++++++++++++++++++++++++++++++++++++------- arch/x86/xen/smp.c | 1 + 3 files changed, 115 insertions(+), 19 deletions(-) (limited to 'arch/x86/xen') diff --git a/arch/x86/xen/Makefile b/arch/x86/xen/Makefile index 7410640db17..3bb4fc21f4f 100644 --- a/arch/x86/xen/Makefile +++ b/arch/x86/xen/Makefile @@ -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 + diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c index eb33aaa8415..76143136dea 100644 --- a/arch/x86/xen/enlighten.c +++ b/arch/x86/xen/enlighten.c @@ -51,6 +51,7 @@ #include #include #include +#include #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(); diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c index 429834ec168..fe03eeed7b4 100644 --- a/arch/x86/xen/smp.c +++ b/arch/x86/xen/smp.c @@ -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 -- cgit v1.2.3-18-g5258 From 4d576b57b50a92801e6493e76e5243d6cff193d2 Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Wed, 9 Sep 2009 12:33:51 -0700 Subject: xen: only enable interrupts while actually blocking for spinlock Where possible we enable interrupts while waiting for a spinlock to become free, in order to reduce big latency spikes in interrupt handling. However, at present if we manage to pick up the spinlock just before blocking, we'll end up holding the lock with interrupts enabled for a while. This will cause a deadlock if we recieve an interrupt in that window, and the interrupt handler tries to take the lock too. Solve this by shrinking the interrupt-enabled region to just around the blocking call. [ Impact: avoid race/deadlock when using Xen PV spinlocks ] Reported-by: "Yang, Xiaowei" Signed-off-by: Jeremy Fitzhardinge --- arch/x86/xen/spinlock.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) (limited to 'arch/x86/xen') diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c index 5601506f2dd..2f91e565192 100644 --- a/arch/x86/xen/spinlock.c +++ b/arch/x86/xen/spinlock.c @@ -187,7 +187,6 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock, bool irq_enabl struct xen_spinlock *prev; int irq = __get_cpu_var(lock_kicker_irq); int ret; - unsigned long flags; u64 start; /* If kicker interrupts not initialized yet, just spin */ @@ -199,16 +198,12 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock, bool irq_enabl /* announce we're spinning */ prev = spinning_lock(xl); - flags = __raw_local_save_flags(); - if (irq_enable) { - ADD_STATS(taken_slow_irqenable, 1); - raw_local_irq_enable(); - } - ADD_STATS(taken_slow, 1); ADD_STATS(taken_slow_nested, prev != NULL); do { + unsigned long flags; + /* clear pending */ xen_clear_irq_pending(irq); @@ -228,6 +223,12 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock, bool irq_enabl goto out; } + flags = __raw_local_save_flags(); + if (irq_enable) { + ADD_STATS(taken_slow_irqenable, 1); + raw_local_irq_enable(); + } + /* * Block until irq becomes pending. If we're * interrupted at this point (after the trylock but @@ -238,13 +239,15 @@ static noinline int xen_spin_lock_slow(struct raw_spinlock *lock, bool irq_enabl * pending. */ xen_poll_irq(irq); + + raw_local_irq_restore(flags); + ADD_STATS(taken_slow_spurious, !xen_test_irq_pending(irq)); } while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */ kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq)); out: - raw_local_irq_restore(flags); unspinning_lock(xl, prev); spin_time_accum_blocked(start); -- cgit v1.2.3-18-g5258 From 2496afbf1e50c70f80992656bcb730c8583ddac3 Mon Sep 17 00:00:00 2001 From: Yang Xiaowei Date: Wed, 9 Sep 2009 12:44:52 -0700 Subject: xen: use stronger barrier after unlocking lock We need to have a stronger barrier between releasing the lock and checking for any waiting spinners. A compiler barrier is not sufficient because the CPU's ordering rules do not prevent the read xl->spinners from happening before the unlock assignment, as they are different memory locations. We need to have an explicit barrier to enforce the write-read ordering to different memory locations. Because of it, I can't bring up > 4 HVM guests on one SMP machine. [ Code and commit comments expanded -J ] [ Impact: avoid deadlock when using Xen PV spinlocks ] Signed-off-by: Yang Xiaowei Signed-off-by: Jeremy Fitzhardinge --- arch/x86/xen/spinlock.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'arch/x86/xen') diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c index 2f91e565192..36a5141108d 100644 --- a/arch/x86/xen/spinlock.c +++ b/arch/x86/xen/spinlock.c @@ -326,8 +326,13 @@ static void xen_spin_unlock(struct raw_spinlock *lock) smp_wmb(); /* make sure no writes get moved after unlock */ xl->lock = 0; /* release lock */ - /* make sure unlock happens before kick */ - barrier(); + /* + * Make sure unlock happens before checking for waiting + * spinners. We need a strong barrier to enforce the + * write-read ordering to different memory locations, as the + * CPU makes no implied guarantees about their ordering. + */ + mb(); if (unlikely(xl->spinners)) xen_spin_unlock_slow(xl); -- cgit v1.2.3-18-g5258