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Commit 36ecafc5 authored by Gregory Fong's avatar Gregory Fong Committed by Ralf Baechle
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MIPS: initial stack protector support 



Implements basic stack protector support based on ARM version in
c743f380 , with Kconfig option,
constant canary value set at boot time, and script to check if
compiler actually supports stack protector.

Tested by creating a kernel module that writes past end of char[].

Signed-off-by: default avatarGregory Fong <gregory.0xf0@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: Filippo Arcidiacono <filippo.arcidiacono@st.com>
Cc: Carmelo Amoroso <carmelo.amoroso@st.com>
Patchwork: https://patchwork.linux-mips.org/patch/5448/


Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 23df3415

arch/mips/Kconfig

+13 −0
Original line number Diff line number Diff line
@@ -2367,6 +2367,19 @@ config SECCOMP 


	  If unsure, say Y. Only embedded should say N here.



config CC_STACKPROTECTOR

	bool "Enable -fstack-protector buffer overflow detection (EXPERIMENTAL)"

	help

	  This option turns on the -fstack-protector GCC feature. This

	  feature puts, at the beginning of functions, a canary value on

	  the stack just before the return address, and validates

	  the value just before actually returning.  Stack based buffer

	  overflows (that need to overwrite this return address) now also

	  overwrite the canary, which gets detected and the attack is then

	  neutralized via a kernel panic.



	  This feature requires gcc version 4.2 or above.



config USE_OF

	bool

	select OF

arch/mips/Makefile

+4 −0
Original line number Diff line number Diff line
@@ -227,6 +227,10 @@ KBUILD_CPPFLAGS += -DDATAOFFSET=$(if $(dataoffset-y),$(dataoffset-y),0) 


LDFLAGS			+= -m $(ld-emul)



ifdef CONFIG_CC_STACKPROTECTOR

  KBUILD_CFLAGS += -fstack-protector

endif



ifdef CONFIG_MIPS

CHECKFLAGS += $(shell $(CC) $(KBUILD_CFLAGS) -dM -E -x c /dev/null | \

	egrep -vw '__GNUC_(|MINOR_|PATCHLEVEL_)_' | \

arch/mips/include/asm/stackprotector.h

0 → 100644
+40 −0
Original line number Diff line number Diff line 
/*

 * GCC stack protector support.

 *

 * (This is directly adopted from the ARM implementation)

 *

 * Stack protector works by putting predefined pattern at the start of

 * the stack frame and verifying that it hasn't been overwritten when

 * returning from the function.  The pattern is called stack canary

 * and gcc expects it to be defined by a global variable called

 * "__stack_chk_guard" on MIPS.  This unfortunately means that on SMP

 * we cannot have a different canary value per task.

 */



#ifndef _ASM_STACKPROTECTOR_H

#define _ASM_STACKPROTECTOR_H 1



#include <linux/random.h>

#include <linux/version.h>



extern unsigned long __stack_chk_guard;



/*

 * Initialize the stackprotector canary value.

 *

 * NOTE: this must only be called from functions that never return,

 * and it must always be inlined.

 */

static __always_inline void boot_init_stack_canary(void)

{

	unsigned long canary;



	/* Try to get a semi random initial value. */

	get_random_bytes(&canary, sizeof(canary));

	canary ^= LINUX_VERSION_CODE;



	current->stack_canary = canary;

	__stack_chk_guard = current->stack_canary;

}



#endif	/* _ASM_STACKPROTECTOR_H */

arch/mips/kernel/process.c

+6 −0
Original line number Diff line number Diff line
@@ -201,6 +201,12 @@ int dump_task_fpu(struct task_struct *t, elf_fpregset_t *fpr) 
	return 1;

}



#ifdef CONFIG_CC_STACKPROTECTOR

#include <linux/stackprotector.h>

unsigned long __stack_chk_guard __read_mostly;

EXPORT_SYMBOL(__stack_chk_guard);

#endif



/*

 *

 */