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RISC-V: Protect all kernel sections including init early

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Currently, .init.text & .init.data are intermixed which makes it impossible
apply different permissions to them. .init.data shouldn't need exec
permissions while .init.text shouldn't have write permission. Moreover,
the strict permission are only enforced /init starts. This leaves the
kernel vulnerable from possible buggy built-in modules.

Keep .init.text & .data in separate sections so that different permissions
are applied to each section. Apply permissions to individual sections as
early as possible. This improves the kernel protection under
CONFIG_STRICT_KERNEL_RWX. We also need to restore the permissions for the
entire _init section after it is freed so that those pages can be used
for other purpose.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Tested-by: Greentime Hu <greentime.hu@sifive.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
This commit is contained in:
Atish Patra 2020-11-04 16:04:38 -08:00 committed by Palmer Dabbelt
parent b6566dc1ac
commit 19a0086902
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GPG key ID: 2E1319F35FBB1889
6 changed files with 68 additions and 28 deletions
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2
arch/riscv/include/asm/sections.h
View file

@ -9,5 +9,7 @@
extern char _start[];
extern char _start_kernel[];
extern char __init_data_begin[], __init_data_end[];
extern char __init_text_begin[], __init_text_end[];
#endif /* __ASM_SECTIONS_H */

4
arch/riscv/include/asm/set_memory.h
View file

@ -15,11 +15,15 @@ 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);
int set_memory_rw_nx(unsigned long addr, int numpages);
void protect_kernel_text_data(void);
#else
static inline int set_memory_ro(unsigned long addr, int numpages) { return 0; }
static inline int set_memory_rw(unsigned long addr, int numpages) { return 0; }
static inline int set_memory_x(unsigned long addr, int numpages) { return 0; }
static inline int set_memory_nx(unsigned long addr, int numpages) { return 0; }
static inline void protect_kernel_text_data(void) {};
static inline int set_memory_rw_nx(unsigned long addr, int numpages) { return 0; }
#endif
int set_direct_map_invalid_noflush(struct page *page);

12
arch/riscv/kernel/setup.c
View file

@ -24,6 +24,7 @@
#include <asm/cpu_ops.h>
#include <asm/early_ioremap.h>
#include <asm/setup.h>
#include <asm/set_memory.h>
#include <asm/sections.h>
#include <asm/sbi.h>
#include <asm/tlbflush.h>
@ -252,6 +253,8 @@ void __init setup_arch(char **cmdline_p)
if (IS_ENABLED(CONFIG_RISCV_SBI))
sbi_init();
if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
protect_kernel_text_data();
#ifdef CONFIG_SWIOTLB
swiotlb_init(1);
#endif
@ -281,3 +284,12 @@ static int __init topology_init(void)
return 0;
}
subsys_initcall(topology_init);
void free_initmem(void)
{
unsigned long init_begin = (unsigned long)__init_begin;
unsigned long init_end = (unsigned long)__init_end;
set_memory_rw_nx(init_begin, (init_end - init_begin) >> PAGE_SHIFT);
free_initmem_default(POISON_FREE_INITMEM);
}

51
arch/riscv/kernel/vmlinux.lds.S
View file

@ -29,6 +29,22 @@ SECTIONS
HEAD_TEXT_SECTION
. = ALIGN(PAGE_SIZE);
.text : {
_text = .;
_stext = .;
TEXT_TEXT
SCHED_TEXT
CPUIDLE_TEXT
LOCK_TEXT
KPROBES_TEXT
ENTRY_TEXT
IRQENTRY_TEXT
SOFTIRQENTRY_TEXT
*(.fixup)
_etext = .;
}
. = ALIGN(SECTION_ALIGN);
__init_begin = .;
__init_text_begin = .;
.init.text : AT(ADDR(.init.text) - LOAD_OFFSET) ALIGN(SECTION_ALIGN) { \
@ -53,36 +69,25 @@ SECTIONS
{
EXIT_TEXT
}
__init_text_end = .;
. = ALIGN(SECTION_ALIGN);
#ifdef CONFIG_EFI
. = ALIGN(PECOFF_SECTION_ALIGNMENT);
__pecoff_text_end = .;
#endif
/* Start of init data section */
__init_data_begin = .;
INIT_DATA_SECTION(16)
.exit.data :
{
EXIT_DATA
}
PERCPU_SECTION(L1_CACHE_BYTES)
__init_data_end = .;
__init_end = .;
. = ALIGN(SECTION_ALIGN);
.text : {
_text = .;
_stext = .;
TEXT_TEXT
SCHED_TEXT
CPUIDLE_TEXT
LOCK_TEXT
KPROBES_TEXT
ENTRY_TEXT
IRQENTRY_TEXT
SOFTIRQENTRY_TEXT
*(.fixup)
_etext = .;
}
#ifdef CONFIG_EFI
. = ALIGN(PECOFF_SECTION_ALIGNMENT);
__pecoff_text_end = .;
#endif
INIT_DATA_SECTION(16)
/* Start of data section */
_sdata = .;
RO_DATA(SECTION_ALIGN)

21
arch/riscv/mm/init.c
View file

@ -612,18 +612,29 @@ static inline void setup_vm_final(void)
#endif /* CONFIG_MMU */
#ifdef CONFIG_STRICT_KERNEL_RWX
void mark_rodata_ro(void)
void protect_kernel_text_data(void)
{
unsigned long text_start = (unsigned long)_text;
unsigned long text_end = (unsigned long)_etext;
unsigned long text_start = (unsigned long)_start;
unsigned long init_text_start = (unsigned long)__init_text_begin;
unsigned long init_data_start = (unsigned long)__init_data_begin;
unsigned long rodata_start = (unsigned long)__start_rodata;
unsigned long data_start = (unsigned long)_data;
unsigned long max_low = (unsigned long)(__va(PFN_PHYS(max_low_pfn)));
set_memory_ro(text_start, (text_end - text_start) >> PAGE_SHIFT);
set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
set_memory_ro(text_start, (init_text_start - text_start) >> PAGE_SHIFT);
set_memory_ro(init_text_start, (init_data_start - init_text_start) >> PAGE_SHIFT);
set_memory_nx(init_data_start, (rodata_start - init_data_start) >> PAGE_SHIFT);
/* rodata section is marked readonly in mark_rodata_ro */
set_memory_nx(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
set_memory_nx(data_start, (max_low - data_start) >> PAGE_SHIFT);
}
void mark_rodata_ro(void)
{
unsigned long rodata_start = (unsigned long)__start_rodata;
unsigned long data_start = (unsigned long)_data;
set_memory_ro(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
debug_checkwx();
}

6
arch/riscv/mm/pageattr.c
View file

@ -128,6 +128,12 @@ static int __set_memory(unsigned long addr, int numpages, pgprot_t set_mask,
return ret;
}
int set_memory_rw_nx(unsigned long addr, int numpages)
{
return __set_memory(addr, numpages, __pgprot(_PAGE_READ | _PAGE_WRITE),
__pgprot(_PAGE_EXEC));
}
int set_memory_ro(unsigned long addr, int numpages)
{
return __set_memory(addr, numpages, __pgprot(_PAGE_READ),