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-rw-r--r--arch/arm/kernel/vmlinux.lds.S10
-rw-r--r--arch/arm/mm/Kconfig34
-rw-r--r--arch/arm/mm/init.c19
3 files changed, 33 insertions, 30 deletions
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 8b60fde5ce48..a6e395c53a48 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -8,7 +8,7 @@
#include <asm/thread_info.h>
#include <asm/memory.h>
#include <asm/page.h>
-#ifdef CONFIG_ARM_KERNMEM_PERMS
+#ifdef CONFIG_DEBUG_RODATA
#include <asm/pgtable.h>
#endif
@@ -94,7 +94,7 @@ SECTIONS
HEAD_TEXT
}
-#ifdef CONFIG_ARM_KERNMEM_PERMS
+#ifdef CONFIG_DEBUG_RODATA
. = ALIGN(1<<SECTION_SHIFT);
#endif
@@ -117,7 +117,7 @@ SECTIONS
ARM_CPU_KEEP(PROC_INFO)
}
-#ifdef CONFIG_DEBUG_RODATA
+#ifdef CONFIG_DEBUG_ALIGN_RODATA
. = ALIGN(1<<SECTION_SHIFT);
#endif
RO_DATA(PAGE_SIZE)
@@ -153,7 +153,7 @@ SECTIONS
_etext = .; /* End of text and rodata section */
#ifndef CONFIG_XIP_KERNEL
-# ifdef CONFIG_ARM_KERNMEM_PERMS
+# ifdef CONFIG_DEBUG_RODATA
. = ALIGN(1<<SECTION_SHIFT);
# else
. = ALIGN(PAGE_SIZE);
@@ -231,7 +231,7 @@ SECTIONS
__data_loc = ALIGN(4); /* location in binary */
. = PAGE_OFFSET + TEXT_OFFSET;
#else
-#ifdef CONFIG_ARM_KERNMEM_PERMS
+#ifdef CONFIG_DEBUG_RODATA
. = ALIGN(1<<SECTION_SHIFT);
#else
. = ALIGN(THREAD_SIZE);
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 549f6d3aec5b..4daeda0a5b7f 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -1037,24 +1037,26 @@ config ARCH_SUPPORTS_BIG_ENDIAN
This option specifies the architecture can support big endian
operation.
-config ARM_KERNMEM_PERMS
- bool "Restrict kernel memory permissions"
+config DEBUG_RODATA
+ bool "Make kernel text and rodata read-only"
depends on MMU
+ default y if CPU_V7
help
- If this is set, kernel memory other than kernel text (and rodata)
- will be made non-executable. The tradeoff is that each region is
- 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.
+ If this is set, kernel text and rodata memory will be made
+ read-only, and non-text kernel memory will be made non-executable.
+ The tradeoff is that each region is padded to section-size (1MiB)
+ boundaries (because their permissions are different and splitting
+ the 1M pages into 4K ones causes TLB performance problems), which
+ can waste memory.
-config DEBUG_RODATA
- bool "Make kernel text and rodata read-only"
- depends on ARM_KERNMEM_PERMS
+config DEBUG_ALIGN_RODATA
+ bool "Make rodata strictly non-executable"
+ depends on DEBUG_RODATA
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.
+ If this is set, rodata will be made explicitly non-executable. This
+ provides protection on the rare chance that attackers might find and
+ use ROP gadgets that exist in the rodata section. This adds an
+ additional section-aligned split of rodata from kernel text so it
+ can be made explicitly non-executable. This padding may waste memory
+ space to gain the additional protection.
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 49bd08178008..53f42508025b 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -572,8 +572,9 @@ void __init mem_init(void)
}
}
-#ifdef CONFIG_ARM_KERNMEM_PERMS
+#ifdef CONFIG_DEBUG_RODATA
struct section_perm {
+ const char *name;
unsigned long start;
unsigned long end;
pmdval_t mask;
@@ -584,6 +585,7 @@ struct section_perm {
static struct section_perm nx_perms[] = {
/* Make pages tables, etc before _stext RW (set NX). */
{
+ .name = "pre-text NX",
.start = PAGE_OFFSET,
.end = (unsigned long)_stext,
.mask = ~PMD_SECT_XN,
@@ -591,14 +593,16 @@ static struct section_perm nx_perms[] = {
},
/* Make init RW (set NX). */
{
+ .name = "init NX",
.start = (unsigned long)__init_begin,
.end = (unsigned long)_sdata,
.mask = ~PMD_SECT_XN,
.prot = PMD_SECT_XN,
},
-#ifdef CONFIG_DEBUG_RODATA
+#ifdef CONFIG_DEBUG_ALIGN_RODATA
/* Make rodata NX (set RO in ro_perms below). */
{
+ .name = "rodata NX",
.start = (unsigned long)__start_rodata,
.end = (unsigned long)__init_begin,
.mask = ~PMD_SECT_XN,
@@ -607,10 +611,10 @@ static struct section_perm nx_perms[] = {
#endif
};
-#ifdef CONFIG_DEBUG_RODATA
static struct section_perm ro_perms[] = {
/* Make kernel code and rodata RX (set RO). */
{
+ .name = "text/rodata RO",
.start = (unsigned long)_stext,
.end = (unsigned long)__init_begin,
#ifdef CONFIG_ARM_LPAE
@@ -623,7 +627,6 @@ static struct section_perm ro_perms[] = {
#endif
},
};
-#endif
/*
* Updates section permissions only for the current mm (sections are
@@ -670,8 +673,8 @@ void set_section_perms(struct section_perm *perms, int n, bool set,
for (i = 0; i < n; i++) {
if (!IS_ALIGNED(perms[i].start, SECTION_SIZE) ||
!IS_ALIGNED(perms[i].end, SECTION_SIZE)) {
- pr_err("BUG: section %lx-%lx not aligned to %lx\n",
- perms[i].start, perms[i].end,
+ pr_err("BUG: %s section %lx-%lx not aligned to %lx\n",
+ perms[i].name, perms[i].start, perms[i].end,
SECTION_SIZE);
continue;
}
@@ -712,7 +715,6 @@ void fix_kernmem_perms(void)
stop_machine(__fix_kernmem_perms, NULL, NULL);
}
-#ifdef CONFIG_DEBUG_RODATA
int __mark_rodata_ro(void *unused)
{
update_sections_early(ro_perms, ARRAY_SIZE(ro_perms));
@@ -735,11 +737,10 @@ void set_kernel_text_ro(void)
set_section_perms(ro_perms, ARRAY_SIZE(ro_perms), true,
current->active_mm);
}
-#endif /* CONFIG_DEBUG_RODATA */
#else
static inline void fix_kernmem_perms(void) { }
-#endif /* CONFIG_ARM_KERNMEM_PERMS */
+#endif /* CONFIG_DEBUG_RODATA */
void free_tcmmem(void)
{