From 60a5317ff0f42dd313094b88f809f63041568b08 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 9 Feb 2009 22:17:40 +0900 Subject: x86: implement x86_32 stack protector Impact: stack protector for x86_32 Implement stack protector for x86_32. GDT entry 28 is used for it. It's set to point to stack_canary-20 and have the length of 24 bytes. CONFIG_CC_STACKPROTECTOR turns off CONFIG_X86_32_LAZY_GS and sets %gs to the stack canary segment on entry. As %gs is otherwise unused by the kernel, the canary can be anywhere. It's defined as a percpu variable. x86_32 exception handlers take register frame on stack directly as struct pt_regs. With -fstack-protector turned on, gcc copies the whole structure after the stack canary and (of course) doesn't copy back on return thus losing all changed. For now, -fno-stack-protector is added to all files which contain those functions. We definitely need something better. Signed-off-by: Tejun Heo Signed-off-by: Ingo Molnar --- arch/x86/kernel/Makefile | 18 ++++++++++++++++++ arch/x86/kernel/cpu/common.c | 17 +++++++++++------ arch/x86/kernel/entry_32.S | 2 +- arch/x86/kernel/head_32.S | 20 +++++++++++++++++++- arch/x86/kernel/process_32.c | 1 + arch/x86/kernel/setup_percpu.c | 2 ++ 6 files changed, 52 insertions(+), 8 deletions(-) (limited to 'arch/x86/kernel') diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile index 37fa30bada1..b1f8be33300 100644 --- a/arch/x86/kernel/Makefile +++ b/arch/x86/kernel/Makefile @@ -24,6 +24,24 @@ CFLAGS_vsyscall_64.o := $(PROFILING) -g0 $(nostackp) CFLAGS_hpet.o := $(nostackp) CFLAGS_tsc.o := $(nostackp) CFLAGS_paravirt.o := $(nostackp) +# +# On x86_32, register frame is passed verbatim on stack as struct +# pt_regs. gcc considers the parameter to belong to the callee and +# with -fstack-protector it copies pt_regs to the callee's stack frame +# to put the structure after the stack canary causing changes made by +# the exception handlers to be lost. Turn off stack protector for all +# files containing functions which take struct pt_regs from register +# frame. +# +# The proper way to fix this is to teach gcc that the argument belongs +# to the caller for these functions, oh well... +# +ifdef CONFIG_X86_32 +CFLAGS_process_32.o := $(nostackp) +CFLAGS_vm86_32.o := $(nostackp) +CFLAGS_signal.o := $(nostackp) +CFLAGS_traps.o := $(nostackp) +endif obj-y := process_$(BITS).o signal.o entry_$(BITS).o obj-y += traps.o irq.o irq_$(BITS).o dumpstack_$(BITS).o diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 41b0de6df87..260fe4cb2c8 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -39,6 +39,7 @@ #include #include #include +#include #include "cpu.h" @@ -122,6 +123,7 @@ DEFINE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page) = { .gdt = { [GDT_ENTRY_ESPFIX_SS] = { { { 0x00000000, 0x00c09200 } } }, [GDT_ENTRY_PERCPU] = { { { 0x0000ffff, 0x00cf9200 } } }, + GDT_STACK_CANARY_INIT #endif } }; EXPORT_PER_CPU_SYMBOL_GPL(gdt_page); @@ -261,6 +263,7 @@ void load_percpu_segment(int cpu) loadsegment(gs, 0); wrmsrl(MSR_GS_BASE, (unsigned long)per_cpu(irq_stack_union.gs_base, cpu)); #endif + load_stack_canary_segment(); } /* Current gdt points %fs at the "master" per-cpu area: after this, @@ -946,16 +949,21 @@ unsigned long kernel_eflags; */ DEFINE_PER_CPU(struct orig_ist, orig_ist); -#else +#else /* x86_64 */ + +#ifdef CONFIG_CC_STACKPROTECTOR +DEFINE_PER_CPU(unsigned long, stack_canary); +#endif -/* Make sure %fs is initialized properly in idle threads */ +/* Make sure %fs and %gs are initialized properly in idle threads */ struct pt_regs * __cpuinit idle_regs(struct pt_regs *regs) { memset(regs, 0, sizeof(struct pt_regs)); regs->fs = __KERNEL_PERCPU; + regs->gs = __KERNEL_STACK_CANARY; return regs; } -#endif +#endif /* x86_64 */ /* * cpu_init() initializes state that is per-CPU. Some data is already @@ -1120,9 +1128,6 @@ void __cpuinit cpu_init(void) __set_tss_desc(cpu, GDT_ENTRY_DOUBLEFAULT_TSS, &doublefault_tss); #endif - /* Clear %gs. */ - asm volatile ("mov %0, %%gs" : : "r" (0)); - /* Clear all 6 debug registers: */ set_debugreg(0, 0); set_debugreg(0, 1); diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S index 82e6868bee4..5f5bd22adcd 100644 --- a/arch/x86/kernel/entry_32.S +++ b/arch/x86/kernel/entry_32.S @@ -186,7 +186,7 @@ /*CFI_REL_OFFSET gs, PT_GS*/ .endm .macro SET_KERNEL_GS reg - xorl \reg, \reg + movl $(__KERNEL_STACK_CANARY), \reg movl \reg, %gs .endm diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S index 24c0e5cd71e..924e31615fb 100644 --- a/arch/x86/kernel/head_32.S +++ b/arch/x86/kernel/head_32.S @@ -19,6 +19,7 @@ #include #include #include +#include /* Physical address */ #define pa(X) ((X) - __PAGE_OFFSET) @@ -437,8 +438,25 @@ is386: movl $2,%ecx # set MP movl $(__KERNEL_PERCPU), %eax movl %eax,%fs # set this cpu's percpu - xorl %eax,%eax # Clear GS and LDT +#ifdef CONFIG_CC_STACKPROTECTOR + /* + * The linker can't handle this by relocation. Manually set + * base address in stack canary segment descriptor. + */ + cmpb $0,ready + jne 1f + movl $per_cpu__gdt_page,%eax + movl $per_cpu__stack_canary,%ecx + movw %cx, 8 * GDT_ENTRY_STACK_CANARY + 2(%eax) + shrl $16, %ecx + movb %cl, 8 * GDT_ENTRY_STACK_CANARY + 4(%eax) + movb %ch, 8 * GDT_ENTRY_STACK_CANARY + 7(%eax) +1: +#endif + movl $(__KERNEL_STACK_CANARY),%eax movl %eax,%gs + + xorl %eax,%eax # Clear LDT lldt %ax cld # gcc2 wants the direction flag cleared at all times diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c index 86122fa2a1b..9a62383e7c3 100644 --- a/arch/x86/kernel/process_32.c +++ b/arch/x86/kernel/process_32.c @@ -212,6 +212,7 @@ int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags) regs.ds = __USER_DS; regs.es = __USER_DS; regs.fs = __KERNEL_PERCPU; + regs.gs = __KERNEL_STACK_CANARY; regs.orig_ax = -1; regs.ip = (unsigned long) kernel_thread_helper; regs.cs = __KERNEL_CS | get_kernel_rpl(); diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c index ef91747bbed..d992e6cff73 100644 --- a/arch/x86/kernel/setup_percpu.c +++ b/arch/x86/kernel/setup_percpu.c @@ -16,6 +16,7 @@ #include #include #include +#include #ifdef CONFIG_DEBUG_PER_CPU_MAPS # define DBG(x...) printk(KERN_DEBUG x) @@ -95,6 +96,7 @@ void __init setup_per_cpu_areas(void) per_cpu(this_cpu_off, cpu) = per_cpu_offset(cpu); per_cpu(cpu_number, cpu) = cpu; setup_percpu_segment(cpu); + setup_stack_canary_segment(cpu); /* * Copy data used in early init routines from the * initial arrays to the per cpu data areas. These -- cgit v1.2.3