[PATCH v2 3/6] RISC-V: Enforce protections for kernel sections early

Atish Patra
2020-10-26T23:03:58Z

Currently, all memblocks are mapped with PAGE_KERNEL_EXEC and the strict
permissions are only enforced after /init starts. This leaves the kernel
vulnerable from possible buggy built-in modules.

Apply permissions to individual sections as early as possible.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
---
arch/riscv/include/asm/set_memory.h | 2 ++
arch/riscv/kernel/setup.c | 2 ++
arch/riscv/mm/init.c | 11 +++++++++--
3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
index 4c5bae7ca01c..4cc3a4e2afd3 100644
--- a/arch/riscv/include/asm/set_memory.h
+++ b/arch/riscv/include/asm/set_memory.h
@@ -15,11 +15,13 @@ 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);
+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) {};
#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 7d6a04ae3929..b722c5bf892c 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 +93,7 @@ void __init setup_arch(char **cmdline_p)
#if IS_ENABLED(CONFIG_RISCV_SBI)
sbi_init();
#endif
+ protect_kernel_text_data();
#ifdef CONFIG_SWIOTLB
swiotlb_init(1);
#endif
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index ea933b789a88..5f196f8158d4 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -608,7 +608,7 @@ 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;
@@ -617,9 +617,16 @@ void mark_rodata_ro(void)
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_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();
}
--
2.25.1