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

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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: Kees Cook <keescook@chromium.org>
Tested-by: Laura Abbott <lauraa@codeaurora.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
This commit is contained in:
Kees Cook 2014-04-03 13:29:50 -07:00
parent 1e6b48116a
commit 80d6b0c2ee
6 changed files with 92 additions and 1 deletions
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10
arch/arm/include/asm/cacheflush.h
View File

@ -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

19
arch/arm/kernel/ftrace.c
View File

@ -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;
}

1
arch/arm/kernel/machine_kexec.c
View File

@ -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;

3
arch/arm/kernel/vmlinux.lds.S
View File

@ -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);

12
arch/arm/mm/Kconfig
View File

@ -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.

48
arch/arm/mm/init.c
View File

@ -622,9 +622,10 @@ struct section_perm {
unsigned long end;
pmdval_t mask;
pmdval_t prot;
pmdval_t clear;
};
struct section_perm nx_perms[] = {
static struct section_perm nx_perms[] = {
/* Make pages tables, etc before _stext RW (set NX). */
{
.start = PAGE_OFFSET,
@ -639,8 +640,35 @@ struct section_perm nx_perms[] = {
.mask = ~PMD_SECT_XN,
.prot = PMD_SECT_XN,
},
#ifdef CONFIG_DEBUG_RODATA
/* Make rodata NX (set RO in ro_perms below). */
{
.start = (unsigned long)__start_rodata,
.end = (unsigned long)__init_begin,
.mask = ~PMD_SECT_XN,
.prot = PMD_SECT_XN,
},
#endif
};
#ifdef CONFIG_DEBUG_RODATA
static struct section_perm ro_perms[] = {
/* Make kernel code and rodata RX (set RO). */
{
.start = (unsigned long)_stext,
.end = (unsigned long)__init_begin,
#ifdef CONFIG_ARM_LPAE
.mask = ~PMD_SECT_RDONLY,
.prot = PMD_SECT_RDONLY,
#else
.mask = ~(PMD_SECT_APX | PMD_SECT_AP_WRITE),
.prot = PMD_SECT_APX | PMD_SECT_AP_WRITE,
.clear = PMD_SECT_AP_WRITE,
#endif
},
};
#endif
/*
* Updates section permissions only for the current mm (sections are
* copied into each mm). During startup, this is the init_mm. Is only
@ -704,6 +732,24 @@ static inline void fix_kernmem_perms(void)
{
set_section_perms(nx_perms, prot);
}
#ifdef CONFIG_DEBUG_RODATA
void mark_rodata_ro(void)
{
set_section_perms(ro_perms, prot);
}
void set_kernel_text_rw(void)
{
set_section_perms(ro_perms, clear);
}
void set_kernel_text_ro(void)
{
set_section_perms(ro_perms, prot);
}
#endif /* CONFIG_DEBUG_RODATA */
#else
static inline void fix_kernmem_perms(void) { }
#endif /* CONFIG_ARM_KERNMEM_PERMS */