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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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9
arch/x86/include/asm/segment.h
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@@ -61,7 +61,7 @@
*
* 26 - ESPFIX small SS
* 27 - per-cpu [ offset to per-cpu data area ]
* 28 - unused
* 28 - stack_canary-20 [ for stack protector ]
* 29 - unused
* 30 - unused
* 31 - TSS for double fault handler
@@ -95,6 +95,13 @@
#define __KERNEL_PERCPU 0
#endif
#define GDT_ENTRY_STACK_CANARY (GDT_ENTRY_KERNEL_BASE + 16)
#ifdef CONFIG_CC_STACKPROTECTOR
#define __KERNEL_STACK_CANARY (GDT_ENTRY_STACK_CANARY * 8)
#else
#define __KERNEL_STACK_CANARY 0
#endif
#define GDT_ENTRY_DOUBLEFAULT_TSS 31
/*