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x86: implement x86_32 stack protector

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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 <tj@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Tejun Heo
2009-02-09 22:17:40 +09:00
committed by Ingo Molnar
parent ccbeed3a05
commit 60a5317ff0
12 changed files with 180 additions and 16 deletions
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17
arch/x86/kernel/cpu/common.c
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@@ -39,6 +39,7 @@
#include <asm/sections.h>
#include <asm/setup.h>
#include <asm/hypervisor.h>
#include <asm/stackprotector.h>
#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 */
/* Make sure %fs is initialized properly in idle threads */
#ifdef CONFIG_CC_STACKPROTECTOR
DEFINE_PER_CPU(unsigned long, stack_canary);
#endif
/* 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);