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Commit 80d6b0c2 authored by Kees Cook's avatar Kees Cook
Browse files

ARM: mm: allow text and rodata sections to be read-only 



This introduces CONFIG_DEBUG_RODATA, making kernel text and rodata
read-only. Additionally, this splits rodata from text so that rodata can
also be NX, which may lead to wasted memory when aligning to SECTION_SIZE.
The read-only areas are made writable during ftrace updates and kexec.

Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Tested-by: default avatarLaura Abbott <lauraa@codeaurora.org>
Acked-by: default avatarNicolas Pitre <nico@linaro.org>
parent 1e6b4811

arch/arm/include/asm/cacheflush.h

+10 −0
Original line number Diff line number Diff line
@@ -487,6 +487,16 @@ int set_memory_rw(unsigned long addr, int numpages); 
int set_memory_x(unsigned long addr, int numpages);

int set_memory_nx(unsigned long addr, int numpages);



#ifdef CONFIG_DEBUG_RODATA

void mark_rodata_ro(void);

void set_kernel_text_rw(void);

void set_kernel_text_ro(void);

#else

static inline void set_kernel_text_rw(void) { }

static inline void set_kernel_text_ro(void) { }

#endif



void flush_uprobe_xol_access(struct page *page, unsigned long uaddr,

			     void *kaddr, unsigned long len);



#endif

arch/arm/kernel/ftrace.c

+19 −0
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 
#include <linux/ftrace.h>

#include <linux/uaccess.h>

#include <linux/module.h>

#include <linux/stop_machine.h>



#include <asm/cacheflush.h>

#include <asm/opcodes.h>
@@ -35,6 +36,22 @@ 


#define	OLD_NOP		0xe1a00000	/* mov r0, r0 */



static int __ftrace_modify_code(void *data)

{

	int *command = data;



	set_kernel_text_rw();

	ftrace_modify_all_code(*command);

	set_kernel_text_ro();



	return 0;

}



void arch_ftrace_update_code(int command)

{

	stop_machine(__ftrace_modify_code, &command, NULL);

}



static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)

{

	return rec->arch.old_mcount ? OLD_NOP : NOP;
@@ -73,6 +90,8 @@ int ftrace_arch_code_modify_prepare(void) 
int ftrace_arch_code_modify_post_process(void)

{

	set_all_modules_text_ro();

	/* Make sure any TLB misses during machine stop are cleared. */

	flush_tlb_all();

	return 0;

}

arch/arm/kernel/machine_kexec.c

+1 −0
Original line number Diff line number Diff line
@@ -164,6 +164,7 @@ void machine_kexec(struct kimage *image) 
	reboot_code_buffer = page_address(image->control_code_page);



	/* Prepare parameters for reboot_code_buffer*/

	set_kernel_text_rw();

	kexec_start_address = image->start;

	kexec_indirection_page = page_list;

	kexec_mach_type = machine_arch_type;

arch/arm/kernel/vmlinux.lds.S

+3 −0
Original line number Diff line number Diff line
@@ -120,6 +120,9 @@ SECTIONS 
			ARM_CPU_KEEP(PROC_INFO)

	}



#ifdef CONFIG_DEBUG_RODATA

	. = ALIGN(1<<SECTION_SHIFT);

#endif

	RO_DATA(PAGE_SIZE)



	. = ALIGN(4);

arch/arm/mm/Kconfig

+12 −0
Original line number Diff line number Diff line
@@ -1017,3 +1017,15 @@ config ARM_KERNMEM_PERMS 
	  padded to section-size (1MiB) boundaries (because their permissions

	  are different and splitting the 1M pages into 4K ones causes TLB

	  performance problems), wasting memory.



config DEBUG_RODATA

	bool "Make kernel text and rodata read-only"

	depends on ARM_KERNMEM_PERMS

	default y

	help

	  If this is set, kernel text and rodata will be made read-only. This

	  is to help catch accidental or malicious attempts to change the

	  kernel's executable code. Additionally splits rodata from kernel

	  text so it can be made explicitly non-executable. This creates

	  another section-size padded region, so it can waste more memory

	  space while gaining the read-only protections.