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

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
......@@ -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
......@@ -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
......@@ -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)
......
......@@ -344,6 +344,7 @@ void __init mem_init(void)
void free_initmem(void)
{
fixup_init();
free_initmem_default(0);
free_alternatives_memory();
}
......
extern void __init bootmem_init(void);
void fixup_init(void);
......@@ -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>
......@@ -59,21 +60,43 @@ 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 {
......@@ -82,9 +105,22 @@ 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;
......@@ -93,8 +129,16 @@ 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);
......@@ -113,21 +157,34 @@ 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));
......@@ -139,8 +196,7 @@ 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))));
......@@ -158,7 +214,7 @@ 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);
......@@ -168,9 +224,10 @@ 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;
......@@ -180,13 +237,23 @@ 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",
......@@ -194,15 +261,71 @@ 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)
{
......@@ -248,14 +371,53 @@ 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.
......@@ -265,6 +427,7 @@ 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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