Commit da141706 authored by Laura Abbott's avatar Laura Abbott Committed by Catalin Marinas
Browse files

arm64: add better page protections to arm64 



Add page protections for arm64 similar to those in arm.
This is for security reasons to prevent certain classes
of exploits. The current method:

- Map all memory as either RWX or RW. We round to the nearest
  section to avoid creating page tables before everything is mapped
- Once everything is mapped, if either end of the RWX section should
  not be X, we split the PMD and remap as necessary
- When initmem is to be freed, we change the permissions back to
  RW (using stop machine if necessary to flush the TLB)
- If CONFIG_DEBUG_RODATA is set, the read only sections are set
  read only.

Acked-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: default avatarKees Cook <keescook@chromium.org>
Tested-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarLaura Abbott <lauraa@codeaurora.org>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 2f896d58

arch/arm64/Kconfig.debug

+23 −0
Original line number Diff line number Diff line
@@ -66,4 +66,27 @@ config DEBUG_SET_MODULE_RONX 
          against certain classes of kernel exploits.

          If in doubt, say "N".



config DEBUG_RODATA

	bool "Make kernel text and rodata read-only"

	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.



          If in doubt, say Y



config DEBUG_ALIGN_RODATA

	depends on DEBUG_RODATA && !ARM64_64K_PAGES

	bool "Align linker sections up to SECTION_SIZE"

	help

	  If this option is enabled, sections that may potentially be marked as

	  read only or non-executable will be aligned up to the section size of

	  the kernel. This prevents sections from being split into pages and

	  avoids a potential TLB penalty. The downside is an increase in

	  alignment and potentially wasted space. Turn on this option if

	  performance is more important than memory pressure.



	  If in doubt, say N



endmenu

arch/arm64/include/asm/cacheflush.h

+5 −0
Original line number Diff line number Diff line
@@ -152,4 +152,9 @@ int set_memory_ro(unsigned long addr, int numpages); 
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);

#endif



#endif

arch/arm64/kernel/vmlinux.lds.S

+15 −2
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ 
#include <asm/thread_info.h>

#include <asm/memory.h>

#include <asm/page.h>

#include <asm/pgtable.h>



#include "image.h"
@@ -49,6 +50,14 @@ PECOFF_FILE_ALIGNMENT = 0x200; 
#define PECOFF_EDATA_PADDING

#endif



#ifdef CONFIG_DEBUG_ALIGN_RODATA

#define ALIGN_DEBUG_RO			. = ALIGN(1<<SECTION_SHIFT);

#define ALIGN_DEBUG_RO_MIN(min)		ALIGN_DEBUG_RO

#else

#define ALIGN_DEBUG_RO

#define ALIGN_DEBUG_RO_MIN(min)		. = ALIGN(min);

#endif



SECTIONS

{

	/*
@@ -71,6 +80,7 @@ SECTIONS 
		_text = .;

		HEAD_TEXT

	}

	ALIGN_DEBUG_RO

	.text : {			/* Real text segment		*/

		_stext = .;		/* Text and read-only data	*/

			__exception_text_start = .;
@@ -87,19 +97,22 @@ SECTIONS 
		*(.got)			/* Global offset table		*/

	}



	ALIGN_DEBUG_RO

	RO_DATA(PAGE_SIZE)

	EXCEPTION_TABLE(8)

	NOTES

	ALIGN_DEBUG_RO

	_etext = .;			/* End of text and rodata section */



	. = ALIGN(PAGE_SIZE);

	ALIGN_DEBUG_RO_MIN(PAGE_SIZE)

	__init_begin = .;



	INIT_TEXT_SECTION(8)

	.exit.text : {

		ARM_EXIT_KEEP(EXIT_TEXT)

	}

	. = ALIGN(16);



	ALIGN_DEBUG_RO_MIN(16)

	.init.data : {

		INIT_DATA

		INIT_SETUP(16)

arch/arm64/mm/init.c

+1 −0
Original line number Diff line number Diff line
@@ -344,6 +344,7 @@ void __init mem_init(void) 


void free_initmem(void)

{

	fixup_init();

	free_initmem_default(0);

	free_alternatives_memory();

}

arch/arm64/mm/mm.h

+2 −0
Original line number Diff line number Diff line 
extern void __init bootmem_init(void);



void fixup_init(void);

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