[PATCHv7 2/2] arm64: add better page protections to arm64
Laura Abbott
lauraa at codeaurora.org
Wed Jan 14 14:59:54 PST 2015
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.
Tested-by: Kees Cook <keescook at chromium.org>
Signed-off-by: Laura Abbott <lauraa at codeaurora.org>
---
v7: Rebased on Ard's patch series. Addressed minor comments from
Catalin.
---
arch/arm64/Kconfig.debug | 23 ++++
arch/arm64/include/asm/cacheflush.h | 5 +
arch/arm64/kernel/vmlinux.lds.S | 17 ++-
arch/arm64/mm/init.c | 1 +
arch/arm64/mm/mm.h | 2 +
arch/arm64/mm/mmu.c | 211 ++++++++++++++++++++++++++++++++----
6 files changed, 233 insertions(+), 26 deletions(-)
diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
index 5fdd6dc..4a87410 100644
--- a/arch/arm64/Kconfig.debug
+++ b/arch/arm64/Kconfig.debug
@@ -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
diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h
index 7ae31a2..67d309c 100644
--- a/arch/arm64/include/asm/cacheflush.h
+++ b/arch/arm64/include/asm/cacheflush.h
@@ -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
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 9965ec8..5d9d2dc 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -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)
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index bac492c..104a60b 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -325,6 +325,7 @@ void __init mem_init(void)
void free_initmem(void)
{
+ fixup_init();
free_initmem_default(0);
free_alternatives_memory();
}
diff --git a/arch/arm64/mm/mm.h b/arch/arm64/mm/mm.h
index 50c3351..ef47d99 100644
--- a/arch/arm64/mm/mm.h
+++ b/arch/arm64/mm/mm.h
@@ -1 +1,3 @@
extern void __init bootmem_init(void);
+
+void fixup_init(void);
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 3286385..e83d30e 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -26,6 +26,7 @@
#include <linux/memblock.h>
#include <linux/fs.h>
#include <linux/io.h>
+#include <linux/stop_machine.h>
#include <asm/cputype.h>
#include <asm/fixmap.h>
@@ -133,21 +134,43 @@ EXPORT_SYMBOL(phys_mem_access_prot);
static void __init *early_alloc(unsigned long sz)
{
void *ptr = __va(memblock_alloc(sz, sz));
+ BUG_ON(!ptr);
memset(ptr, 0, sz);
return ptr;
}
-static void __init alloc_init_pte(pmd_t *pmd, unsigned long addr,
+/*
+ * remap a PMD into pages
+ */
+static void split_pmd(pmd_t *pmd, pte_t *pte)
+{
+ unsigned long pfn = pmd_pfn(*pmd);
+ int i = 0;
+
+ do {
+ /*
+ * Need to have the least restrictive permissions available
+ * permissions will be fixed up later
+ */
+ set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC));
+ pfn++;
+ } while (pte++, i++, i < PTRS_PER_PTE);
+}
+
+static void alloc_init_pte(pmd_t *pmd, unsigned long addr,
unsigned long end, unsigned long pfn,
- pgprot_t prot)
+ pgprot_t prot,
+ void *(*alloc)(unsigned long size))
{
pte_t *pte;
- if (pmd_none(*pmd)) {
- pte = early_alloc(PTRS_PER_PTE * sizeof(pte_t));
+ if (pmd_none(*pmd) || pmd_bad(*pmd)) {
+ pte = alloc(PTRS_PER_PTE * sizeof(pte_t));
+ if (pmd_sect(*pmd))
+ split_pmd(pmd, pte);
__pmd_populate(pmd, __pa(pte), PMD_TYPE_TABLE);
+ flush_tlb_all();
}
- BUG_ON(pmd_bad(*pmd));
pte = pte_offset_kernel(pmd, addr);
do {
@@ -156,9 +179,22 @@ static void __init alloc_init_pte(pmd_t *pmd, unsigned long addr,
} while (pte++, addr += PAGE_SIZE, addr != end);
}
-static void __init alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
+void split_pud(pud_t *old_pud, pmd_t *pmd)
+{
+ unsigned long addr = pud_pfn(*old_pud) << PAGE_SHIFT;
+ pgprot_t prot = __pgprot(pud_val(*old_pud) ^ addr);
+ int i = 0;
+
+ do {
+ set_pmd(pmd, __pmd(addr | prot));
+ addr += PMD_SIZE;
+ } while (pmd++, i++, i < PTRS_PER_PMD);
+}
+
+static void alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
unsigned long addr, unsigned long end,
- phys_addr_t phys, pgprot_t prot)
+ phys_addr_t phys, pgprot_t prot,
+ void *(*alloc)(unsigned long size))
{
pmd_t *pmd;
unsigned long next;
@@ -167,8 +203,16 @@ static void __init alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
* Check for initial section mappings in the pgd/pud and remove them.
*/
if (pud_none(*pud) || pud_bad(*pud)) {
- pmd = early_alloc(PTRS_PER_PMD * sizeof(pmd_t));
+ pmd = alloc(PTRS_PER_PMD * sizeof(pmd_t));
+ if (pud_sect(*pud)) {
+ /*
+ * need to have the 1G of mappings continue to be
+ * present
+ */
+ split_pud(pud, pmd);
+ }
pud_populate(mm, pud, pmd);
+ flush_tlb_all();
}
pmd = pmd_offset(pud, addr);
@@ -187,21 +231,34 @@ static void __init alloc_init_pmd(struct mm_struct *mm, pud_t *pud,
flush_tlb_all();
} else {
alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys),
- prot);
+ prot, alloc);
}
phys += next - addr;
} while (pmd++, addr = next, addr != end);
}
-static void __init alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
+static inline bool use_1G_block(unsigned long addr, unsigned long next,
+ unsigned long phys)
+{
+ if (PAGE_SHIFT != 12)
+ return false;
+
+ if (((addr | next | phys) & ~PUD_MASK) != 0)
+ return false;
+
+ return true;
+}
+
+static void alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
unsigned long addr, unsigned long end,
- phys_addr_t phys, pgprot_t prot)
+ phys_addr_t phys, pgprot_t prot,
+ void *(*alloc)(unsigned long size))
{
pud_t *pud;
unsigned long next;
if (pgd_none(*pgd)) {
- pud = early_alloc(PTRS_PER_PUD * sizeof(pud_t));
+ pud = alloc(PTRS_PER_PUD * sizeof(pud_t));
pgd_populate(mm, pgd, pud);
}
BUG_ON(pgd_bad(*pgd));
@@ -213,8 +270,7 @@ static void __init alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
/*
* For 4K granule only, attempt to put down a 1GB block
*/
- if ((PAGE_SHIFT == 12) &&
- ((addr | next | phys) & ~PUD_MASK) == 0) {
+ if (use_1G_block(addr, next, phys)) {
pud_t old_pud = *pud;
set_pud(pud, __pud(phys |
pgprot_val(mk_sect_prot(prot))));
@@ -232,7 +288,7 @@ static void __init alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
flush_tlb_all();
}
} else {
- alloc_init_pmd(mm, pud, addr, next, phys, prot);
+ alloc_init_pmd(mm, pud, addr, next, phys, prot, alloc);
}
phys += next - addr;
} while (pud++, addr = next, addr != end);
@@ -242,9 +298,10 @@ static void __init alloc_init_pud(struct mm_struct *mm, pgd_t *pgd,
* Create the page directory entries and any necessary page tables for the
* mapping specified by 'md'.
*/
-static void __init __create_mapping(struct mm_struct *mm, pgd_t *pgd,
+static void __create_mapping(struct mm_struct *mm, pgd_t *pgd,
phys_addr_t phys, unsigned long virt,
- phys_addr_t size, pgprot_t prot)
+ phys_addr_t size, pgprot_t prot,
+ void *(*alloc)(unsigned long size))
{
unsigned long addr, length, end, next;
@@ -254,13 +311,23 @@ static void __init __create_mapping(struct mm_struct *mm, pgd_t *pgd,
end = addr + length;
do {
next = pgd_addr_end(addr, end);
- alloc_init_pud(mm, pgd, addr, next, phys, prot);
+ alloc_init_pud(mm, pgd, addr, next, phys, prot, alloc);
phys += next - addr;
} while (pgd++, addr = next, addr != end);
}
-static void __init create_mapping(phys_addr_t phys, unsigned long virt,
- phys_addr_t size)
+static void *late_alloc(unsigned long size)
+{
+ void *ptr;
+
+ BUG_ON(size > PAGE_SIZE);
+ ptr = (void *)__get_free_page(PGALLOC_GFP);
+ BUG_ON(!ptr);
+ return ptr;
+}
+
+static void __ref create_mapping(phys_addr_t phys, unsigned long virt,
+ phys_addr_t size, pgprot_t prot)
{
if (virt < VMALLOC_START) {
pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
@@ -268,15 +335,71 @@ static void __init create_mapping(phys_addr_t phys, unsigned long virt,
return;
}
__create_mapping(&init_mm, pgd_offset_k(virt & PAGE_MASK), phys, virt,
- size, PAGE_KERNEL_EXEC);
+ size, prot, early_alloc);
}
void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
unsigned long virt, phys_addr_t size,
pgprot_t prot)
{
- __create_mapping(mm, pgd_offset(mm, virt), phys, virt, size, prot);
+ __create_mapping(mm, pgd_offset(mm, virt), phys, virt, size, prot,
+ early_alloc);
+}
+
+static void create_mapping_late(phys_addr_t phys, unsigned long virt,
+ phys_addr_t size, pgprot_t prot)
+{
+ if (virt < VMALLOC_START) {
+ pr_warn("BUG: not creating mapping for %pa at 0x%016lx - outside kernel range\n",
+ &phys, virt);
+ return;
+ }
+
+ return __create_mapping(&init_mm, pgd_offset_k(virt & PAGE_MASK),
+ phys, virt, size, prot, late_alloc);
+}
+
+#ifdef CONFIG_DEBUG_RODATA
+static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
+{
+ /*
+ * Set up the executable regions using the existing section mappings
+ * for now. This will get more fine grained later once all memory
+ * is mapped
+ */
+ unsigned long kernel_x_start = round_down(__pa(_stext), SECTION_SIZE);
+ unsigned long kernel_x_end = round_up(__pa(__init_end), SECTION_SIZE);
+
+ if (end < kernel_x_start) {
+ create_mapping(start, __phys_to_virt(start),
+ end - start, PAGE_KERNEL);
+ } else if (start >= kernel_x_end) {
+ create_mapping(start, __phys_to_virt(start),
+ end - start, PAGE_KERNEL);
+ } else {
+ if (start < kernel_x_start)
+ create_mapping(start, __phys_to_virt(start),
+ kernel_x_start - start,
+ PAGE_KERNEL);
+ create_mapping(kernel_x_start,
+ __phys_to_virt(kernel_x_start),
+ kernel_x_end - kernel_x_start,
+ PAGE_KERNEL_EXEC);
+ if (kernel_x_end < end)
+ create_mapping(kernel_x_end,
+ __phys_to_virt(kernel_x_end),
+ end - kernel_x_end,
+ PAGE_KERNEL);
+ }
+
+}
+#else
+static void __init __map_memblock(phys_addr_t start, phys_addr_t end)
+{
+ create_mapping(start, __phys_to_virt(start), end - start,
+ PAGE_KERNEL_EXEC);
}
+#endif
static void __init map_mem(void)
{
@@ -322,14 +445,53 @@ static void __init map_mem(void)
memblock_set_current_limit(limit);
}
#endif
-
- create_mapping(start, __phys_to_virt(start), end - start);
+ __map_memblock(start, end);
}
/* Limit no longer required. */
memblock_set_current_limit(MEMBLOCK_ALLOC_ANYWHERE);
}
+void __init fixup_executable(void)
+{
+#ifdef CONFIG_DEBUG_RODATA
+ /* now that we are actually fully mapped, make the start/end more fine grained */
+ if (!IS_ALIGNED((unsigned long)_stext, SECTION_SIZE)) {
+ unsigned long aligned_start = round_down(__pa(_stext),
+ SECTION_SIZE);
+
+ create_mapping(aligned_start, __phys_to_virt(aligned_start),
+ __pa(_stext) - aligned_start,
+ PAGE_KERNEL);
+ }
+
+ if (!IS_ALIGNED((unsigned long)__init_end, SECTION_SIZE)) {
+ unsigned long aligned_end = round_up(__pa(__init_end),
+ SECTION_SIZE);
+ create_mapping(__pa(__init_end), (unsigned long)__init_end,
+ aligned_end - __pa(__init_end),
+ PAGE_KERNEL);
+ }
+#endif
+}
+
+#ifdef CONFIG_DEBUG_RODATA
+void mark_rodata_ro(void)
+{
+ create_mapping_late(__pa(_stext), (unsigned long)_stext,
+ (unsigned long)_etext - (unsigned long)_stext,
+ PAGE_KERNEL_EXEC | PTE_RDONLY);
+
+}
+#endif
+
+void fixup_init(void)
+{
+ create_mapping_late(__pa(__init_begin), (unsigned long)__init_begin,
+ (unsigned long)__init_end - (unsigned long)__init_begin,
+ PAGE_KERNEL);
+}
+
/*
* paging_init() sets up the page tables, initialises the zone memory
* maps and sets up the zero page.
@@ -339,6 +501,7 @@ void __init paging_init(void)
void *zero_page;
map_mem();
+ fixup_executable();
/*
* Finally flush the caches and tlb to ensure that we're in a
--
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