[PATCH v3 4/5] RISC-V: Protect all kernel sections including init early

From: Atish Patra
Date: Wed Nov 04 2020 - 19:05:09 EST

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@xxxxxxx>
---
arch/riscv/include/asm/sections.h | 2 ++
arch/riscv/include/asm/set_memory.h | 4 +++
arch/riscv/kernel/setup.c | 12 +++++++
arch/riscv/kernel/vmlinux.lds.S | 49 ++++++++++++++++-------------
arch/riscv/mm/init.c | 21 ++++++++++---
arch/riscv/mm/pageattr.c | 6 ++++
6 files changed, 67 insertions(+), 27 deletions(-)

diff --git a/arch/riscv/include/asm/sections.h b/arch/riscv/include/asm/sections.h
index 3a9971b1210f..1595c5b60cfd 100644
--- a/arch/riscv/include/asm/sections.h
+++ b/arch/riscv/include/asm/sections.h
@@ -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 */
diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
index 4c5bae7ca01c..b21f4bea6434 100644
--- a/arch/riscv/include/asm/set_memory.h
+++ b/arch/riscv/include/asm/set_memory.h
@@ -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);
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index b916f4a904c4..0cbbf62c7747 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -22,6 +22,7 @@
#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>
@@ -92,6 +93,8 @@ 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
@@ -121,3 +124,12 @@ 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);
+}
diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index cacd7898ba7f..ca19ee5acd0a 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -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) { \
@@ -53,35 +69,24 @@ SECTIONS
{
EXIT_TEXT
}
- .exit.data :
- {
- EXIT_DATA
- }
- PERCPU_SECTION(L1_CACHE_BYTES)
- __init_end = .;

+ __init_text_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
-
+ /* 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 = .;

/* Start of data section */
_sdata = .;
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 0d13d0c36a7d..00793f3c837e 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -622,18 +622,29 @@ 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();
}
diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
index 19fecb362d81..c64ec224fd0c 100644
--- a/arch/riscv/mm/pageattr.c
+++ b/arch/riscv/mm/pageattr.c
@@ -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),
--
2.25.1