[PATCH v2] arch: um: implement memory protection

[PATCH v2] arch: um: implement memory protection

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

Implement memory protection, namely
 * ARCH_HAS_SET_MEMORY
 * ARCH_HAS_STRICT_KERNEL_RWX
 * ARCH_HAS_STRICT_MODULE_RWX

The .text section is marked as RO.
The rodata is marked as RO & NX.
The remaining data is marked NX.

Move the .kstrtab to be covered by the NX.

Note that you can now enable CONFIG_DEBUG_RODATA_TEST,
but it's broken as the fixup is broken - it'll just
crash with

 Kernel panic - not syncing: Segfault with no mm

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
v2: include forgotten file
---
 arch/um/Kconfig                  |  3 ++
 arch/um/include/asm/pgtable.h    |  2 +
 arch/um/include/asm/set_memory.h |  1 +
 arch/um/kernel/dyn.lds.S         |  4 +-
 arch/um/kernel/mem.c             | 76 ++++++++++++++++++++++++++++++++
 5 files changed, 84 insertions(+), 2 deletions(-)
 create mode 100644 arch/um/include/asm/set_memory.h

diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index 3c3adfc486f2..e84264be26c9 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -18,6 +18,9 @@ config UML
 	select GENERIC_CLOCKEVENTS
 	select HAVE_GCC_PLUGINS
 	select TTY # Needed for line.c
+	select ARCH_HAS_SET_MEMORY
+	select ARCH_HAS_STRICT_KERNEL_RWX
+	select ARCH_HAS_STRICT_MODULE_RWX
 
 config MMU
 	bool
diff --git a/arch/um/include/asm/pgtable.h b/arch/um/include/asm/pgtable.h
index b377df76cc28..0e6cda3516c6 100644
--- a/arch/um/include/asm/pgtable.h
+++ b/arch/um/include/asm/pgtable.h
@@ -17,6 +17,8 @@
 #define _PAGE_USER	0x040
 #define _PAGE_ACCESSED	0x080
 #define _PAGE_DIRTY	0x100
+#define _PAGE_RO	0x200
+#define _PAGE_NX	0x400
 /* If _PAGE_PRESENT is clear, we use these: */
 #define _PAGE_PROTNONE	0x010	/* if the user mapped it with PROT_NONE;
 				   pte_present gives true */
diff --git a/arch/um/include/asm/set_memory.h b/arch/um/include/asm/set_memory.h
new file mode 100644
index 000000000000..24266c63720d
--- /dev/null
+++ b/arch/um/include/asm/set_memory.h
@@ -0,0 +1 @@
+#include <asm-generic/set_memory.h>
diff --git a/arch/um/kernel/dyn.lds.S b/arch/um/kernel/dyn.lds.S
index c69d69ee96be..da6b42793e0a 100644
--- a/arch/um/kernel/dyn.lds.S
+++ b/arch/um/kernel/dyn.lds.S
@@ -89,10 +89,10 @@ SECTIONS
     KEEP (*(.fini))
   } =0x90909090
 
-  .kstrtab : { *(.kstrtab) }
-
   #include <asm/common.lds.S>
 
+  .kstrtab : { *(.kstrtab) }
+
   __init_begin = .;
   init.data : { INIT_DATA }
   __init_end = .;
diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
index f256be1d77bd..7ce445bfa58f 100644
--- a/arch/um/kernel/mem.c
+++ b/arch/um/kernel/mem.c
@@ -10,6 +10,7 @@
 #include <linux/mm.h>
 #include <linux/swap.h>
 #include <linux/slab.h>
+#include <asm/set_memory.h>
 #include <asm/fixmap.h>
 #include <asm/page.h>
 #include <as-layout.h>
@@ -37,6 +38,22 @@ int kmalloc_ok = 0;
 /* Used during early boot */
 static unsigned long brk_end;
 
+void mark_rodata_ro(void)
+{
+	unsigned long text_start = PFN_ALIGN(_text);
+	unsigned long rodata_start = PFN_ALIGN(__start_rodata);
+	unsigned long rodata_end = PFN_ALIGN(&__end_rodata);
+	unsigned long all_end = PFN_ALIGN(&__bss_stop);
+
+	printk(KERN_INFO "Write protecting the kernel read-only data: %luk\n",
+	       (rodata_end - text_start) >> 10);
+
+	set_memory_ro(text_start,
+		      (rodata_end - text_start) >> PAGE_SHIFT);
+	set_memory_nx(rodata_start,
+		      (all_end - rodata_start) >> PAGE_SHIFT);
+}
+
 void __init mem_init(void)
 {
 	/* clear the zero-page */
@@ -225,3 +242,62 @@ void *uml_kmalloc(int size, int flags)
 {
 	return kmalloc(size, flags);
 }
+
+struct page_change_data {
+	u32 set, clear;
+};
+
+static int change_page_range(pte_t *ptep, unsigned long addr, void *data)
+{
+	struct page_change_data *cdata = data;
+	pte_t pte = READ_ONCE(*ptep);
+
+	pte_clear_bits(pte, cdata->clear);
+	pte_set_bits(pte, cdata->set);
+
+	set_pte(ptep, pte);
+
+	os_protect_memory((void *)addr, PAGE_SIZE,
+			  1, !(pte.pte & _PAGE_RO), !(pte.pte & _PAGE_NX));
+	return 0;
+}
+
+static int change_memory_common(unsigned long addr, int numpages,
+				u32 set, u32 clear)
+{
+	unsigned long start = addr & PAGE_MASK;
+	unsigned long end = PAGE_ALIGN(addr) + numpages * PAGE_SIZE;
+	unsigned long size = end - start;
+	struct page_change_data data;
+
+	WARN_ON_ONCE(start != addr);
+
+	if (!size)
+		return 0;
+
+	data.set = set;
+	data.clear = clear;
+
+	return apply_to_page_range(&init_mm, start, size, change_page_range,
+				   &data);
+}
+
+int set_memory_ro(unsigned long addr, int numpages)
+{
+	return change_memory_common(addr, numpages, _PAGE_RO, 0);
+}
+
+int set_memory_rw(unsigned long addr, int numpages)
+{
+	return change_memory_common(addr, numpages, 0, _PAGE_RO);
+}
+
+int set_memory_nx(unsigned long addr, int numpages)
+{
+	return change_memory_common(addr, numpages, _PAGE_NX, 0);
+}
+
+int set_memory_x(unsigned long addr, int numpages)
+{
+	return change_memory_common(addr, numpages, 0, _PAGE_NX);
+}
-- 
2.20.1


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