[PATCH 1/2] ARM: mm: mark non-text sections non-executable
From: Kees Cook
Date: Thu Apr 03 2014 - 22:17:28 EST
Adds CONFIG_ARM_KERNMEM_PERMS to separate the kernel memory regions
into section-sized areas that can have different permisions. Performs
the NX permission changes during free_initmem, so that init memory can be
reclaimed.
This uses section size instead of PMD size to reduce memory caps on
non-LPAE systems.
Based on work by Brad Spengler, Larry Bassel, and Laura Abbott.
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
arch/arm/kernel/vmlinux.lds.S | 17 ++++++++
arch/arm/mm/Kconfig | 9 ++++
arch/arm/mm/init.c | 92 +++++++++++++++++++++++++++++++++++++++++
arch/arm/mm/mmu.c | 13 +++++-
4 files changed, 130 insertions(+), 1 deletion(-)
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 7bcee5c9b604..08fa667ef2f1 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -8,6 +8,9 @@
#include <asm/thread_info.h>
#include <asm/memory.h>
#include <asm/page.h>
+#ifdef CONFIG_ARM_KERNMEM_PERMS
+#include <asm/pgtable.h>
+#endif
#define PROC_INFO \
. = ALIGN(4); \
@@ -90,6 +93,11 @@ SECTIONS
_text = .;
HEAD_TEXT
}
+
+#ifdef CONFIG_ARM_KERNMEM_PERMS
+ . = ALIGN(1<<SECTION_SHIFT);
+#endif
+
.text : { /* Real text segment */
_stext = .; /* Text and read-only data */
__exception_text_start = .;
@@ -145,7 +153,11 @@ SECTIONS
_etext = .; /* End of text and rodata section */
#ifndef CONFIG_XIP_KERNEL
+# ifdef CONFIG_ARM_KERNMEM_PERMS
+ . = ALIGN(1<<SECTION_SHIFT);
+# else
. = ALIGN(PAGE_SIZE);
+# endif
__init_begin = .;
#endif
/*
@@ -220,7 +232,12 @@ SECTIONS
. = PAGE_OFFSET + TEXT_OFFSET;
#else
__init_end = .;
+
+#ifdef CONFIG_ARM_KERNMEM_PERMS
+ . = ALIGN(1<<SECTION_SHIFT);
+#else
. = ALIGN(THREAD_SIZE);
+#endif
__data_loc = .;
#endif
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 1f8fed94c2a4..8848d7b73e66 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -958,3 +958,12 @@ config ARCH_SUPPORTS_BIG_ENDIAN
help
This option specifies the architecture can support big endian
operation.
+
+config ARM_KERNMEM_PERMS
+ bool "Restrict kernel memory permissions"
+ 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.
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 804d61566a53..8539eb2a01ad 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -31,6 +31,11 @@
#include <asm/tlb.h>
#include <asm/fixmap.h>
+#ifdef CONFIG_ARM_KERNMEM_PERMS
+#include <asm/system_info.h>
+#include <asm/cp15.h>
+#endif
+
#include <asm/mach/arch.h>
#include <asm/mach/map.h>
@@ -621,11 +626,98 @@ void __init mem_init(void)
}
}
+#ifdef CONFIG_ARM_KERNMEM_PERMS
+struct section_perm {
+ unsigned long start;
+ unsigned long end;
+ pmdval_t mask;
+ pmdval_t prot;
+};
+
+struct section_perm section_perms[] = {
+ /* Make pages tables, etc before _stext RW (set NX). */
+ {
+ .start = PAGE_OFFSET,
+ .end = (unsigned long)_stext,
+ .mask = ~PMD_SECT_XN,
+ .prot = PMD_SECT_XN,
+ },
+ /* Make init RW (set NX). */
+ {
+ .start = (unsigned long)__init_begin,
+ .end = (unsigned long)_sdata,
+ .mask = ~PMD_SECT_XN,
+ .prot = PMD_SECT_XN,
+ },
+};
+
+static inline void section_update(unsigned long addr, pmdval_t mask,
+ pmdval_t prot)
+{
+ pmd_t *pmd = pmd_off_k(addr);
+
+#ifdef CONFIG_ARM_LPAE
+ pmd[0] = __pmd((pmd_val(pmd[0]) & mask) | prot);
+#else
+ if (addr & SECTION_SIZE)
+ pmd[1] = __pmd((pmd_val(pmd[1]) & mask) | prot);
+ else
+ pmd[0] = __pmd((pmd_val(pmd[0]) & mask) | prot);
+#endif
+ flush_pmd_entry(pmd);
+}
+
+static inline bool arch_has_strict_perms(void)
+{
+ unsigned int cr;
+
+ if (cpu_architecture() < CPU_ARCH_ARMv6)
+ return false;
+
+ cr = get_cr();
+ if (!(cr & CR_XP))
+ return false;
+
+ return true;
+}
+
+static inline void fix_kernmem_perms(void)
+{
+ unsigned long addr;
+ unsigned int i;
+
+ if (!arch_has_strict_perms())
+ return;
+
+ for (i = 0; i < ARRAY_SIZE(section_perms); i++) {
+ if (!IS_ALIGNED(section_perms[i].start, SECTION_SIZE) ||
+ !IS_ALIGNED(section_perms[i].end, SECTION_SIZE)) {
+ pr_err("BUG: section %lx-%lx not aligned to %lx\n",
+ section_perms[i].start, section_perms[i].end,
+ SECTION_SIZE);
+ continue;
+ }
+
+ for (addr = section_perms[i].start;
+ addr < section_perms[i].end;
+ addr += SECTION_SIZE)
+ section_update(addr, section_perms[i].mask,
+ section_perms[i].prot);
+ }
+}
+#else
+static inline void fix_kernmem_perms(void) { }
+#endif /* CONFIG_ARM_KERNMEM_PERMS */
+
void free_initmem(void)
{
#ifdef CONFIG_HAVE_TCM
extern char __tcm_start, __tcm_end;
+#endif
+
+ fix_kernmem_perms();
+#ifdef CONFIG_HAVE_TCM
poison_init_mem(&__tcm_start, &__tcm_end - &__tcm_start);
free_reserved_area(&__tcm_start, &__tcm_end, -1, "TCM link");
#endif
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index a623cb3ad012..9d89de8cc349 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1369,13 +1369,24 @@ static void __init map_lowmem(void)
if (start >= end)
break;
- if (end < kernel_x_start || start >= kernel_x_end) {
+ if (end < kernel_x_start) {
map.pfn = __phys_to_pfn(start);
map.virtual = __phys_to_virt(start);
map.length = end - start;
map.type = MT_MEMORY_RWX;
create_mapping(&map);
+ } else if (start >= kernel_x_end) {
+ map.pfn = __phys_to_pfn(start);
+ map.virtual = __phys_to_virt(start);
+ map.length = end - start;
+#ifdef CONFIG_ARM_KERNMEM_PERMS
+ map.type = MT_MEMORY_RW;
+#else
+ map.type = MT_MEMORY_RWX;
+#endif
+
+ create_mapping(&map);
} else {
/* This better cover the entire kernel */
if (start < kernel_x_start) {
--
1.7.9.5
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