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 <tj@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5bcdede..f760a22 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -209,7 +209,7 @@
config X86_32_LAZY_GS
def_bool y
- depends on X86_32
+ depends on X86_32 && !CC_STACKPROTECTOR
config KTIME_SCALAR
def_bool X86_32
@@ -1356,7 +1356,6 @@
config CC_STACKPROTECTOR
bool "Enable -fstack-protector buffer overflow detection (EXPERIMENTAL)"
- depends on X86_64
select CC_STACKPROTECTOR_ALL
help
This option turns on the -fstack-protector GCC feature. This