On 06/07/2016 02:57 PM, Kees Cook wrote:
This adds a function that lives in the .rodata section. The section
flags are corrected using objcopy since there is no way with gcc to
declare section flags in an architecture-agnostic way.
Permit me to be the bearer of bad architecture news once again. With
arm64 cross compiler (both Fedora 6.1.1 and Linaro 5.1)
CC drivers/misc/lkdtm_rodata.o
OBJCOPY drivers/misc/lkdtm_rodata_objcopy.o
LD drivers/misc/lkdtm.o
drivers/misc/lkdtm_rodata_objcopy.o: file not recognized: File format not
recognized
scripts/Makefile.build:423: recipe for target 'drivers/misc/lkdtm.o' failed
make[2]: *** [drivers/misc/lkdtm.o] Error 1
scripts/Makefile.build:440: recipe for target 'drivers/misc' failed
make[1]: *** [drivers/misc] Error 2
Makefile:985: recipe for target 'drivers' failed
make: *** [drivers] Error 2
As far as I can tell this is because arm64 defines OBJCOPYFLAGS and they get
propagated to objcopy
aarch64-linux-gnu-objcopy -O binary -R .note -R .note.gnu.build-id -R .comment
-S --set-section-flags .text=alloc,readonly
--rename-section .text=.rodata drivers/misc/lkdtm_rodata.o
drivers/misc/lkdtm_rodata_objcopy.o
vs x86
objcopy --set-section-flags .text=alloc,readonly --rename-section .text=.rodata
drivers/misc/lkdtm_rodata.o drivers/misc/lkdtm_rodata_objcopy.o
specifically it's the -O binary that seems to break things, the same failure
happens on x86 as well with the the same commands. It works if I clear out
the OBJCOPYFLAGS variable first but I don't think that's the correct way to
fix this.
Thanks,
Laura
Signed-off-by: Kees Cook <[email protected]>
---
drivers/misc/Makefile | 7 +++++++
drivers/misc/lkdtm.h | 6 ++++++
drivers/misc/lkdtm_core.c | 24 +++++++++++++++++-------
drivers/misc/lkdtm_rodata.c | 10 ++++++++++
4 files changed, 40 insertions(+), 7 deletions(-)
create mode 100644 drivers/misc/lkdtm.h
create mode 100644 drivers/misc/lkdtm_rodata.c
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index c3cb6ad8cc37..b2d3d68dfa22 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -59,3 +59,10 @@ obj-$(CONFIG_CXL_BASE) += cxl/
obj-$(CONFIG_PANEL) += panel.o
lkdtm-$(CONFIG_LKDTM) += lkdtm_core.o
+lkdtm-$(CONFIG_LKDTM) += lkdtm_rodata_objcopy.o
+
+OBJCOPYFLAGS_lkdtm_rodata_objcopy.o := \
+ --set-section-flags .text=alloc,readonly \
+ --rename-section .text=.rodata
+$(obj)/lkdtm_rodata_objcopy.o: $(obj)/lkdtm_rodata.o
+ $(call if_changed,objcopy)
diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h
new file mode 100644
index 000000000000..9531fa3be4c3
--- /dev/null
+++ b/drivers/misc/lkdtm.h
@@ -0,0 +1,6 @@
+#ifndef __LKDTM_H
+#define __LKDTM_H
+
+void lkdtm_rodata_do_nothing(void);
+
+#endif
diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
index 605050c60f10..187cd9b63e9a 100644
--- a/drivers/misc/lkdtm_core.c
+++ b/drivers/misc/lkdtm_core.c
@@ -52,6 +52,8 @@
#include <linux/ide.h>
#endif
+#include "lkdtm.h"
+
/*
* Make sure our attempts to over run the kernel stack doesn't trigger
* a compiler warning when CONFIG_FRAME_WARN is set. Then make sure we
@@ -103,6 +105,7 @@ enum ctype {
CT_EXEC_STACK,
CT_EXEC_KMALLOC,
CT_EXEC_VMALLOC,
+ CT_EXEC_RODATA,
CT_EXEC_USERSPACE,
CT_ACCESS_USERSPACE,
CT_WRITE_RO,
@@ -145,6 +148,7 @@ static char* cp_type[] = {
"EXEC_STACK",
"EXEC_KMALLOC",
"EXEC_VMALLOC",
+ "EXEC_RODATA",
"EXEC_USERSPACE",
"ACCESS_USERSPACE",
"WRITE_RO",
@@ -346,15 +350,18 @@ static noinline void corrupt_stack(void)
memset((void *)data, 0, 64);
}
-static void noinline execute_location(void *dst)
+static noinline void execute_location(void *dst, bool write)
{
void (*func)(void) = dst;
pr_info("attempting ok execution at %p\n", do_nothing);
do_nothing();
- memcpy(dst, do_nothing, EXEC_SIZE);
- flush_icache_range((unsigned long)dst, (unsigned long)dst + EXEC_SIZE);
+ if (write) {
+ memcpy(dst, do_nothing, EXEC_SIZE);
+ flush_icache_range((unsigned long)dst,
+ (unsigned long)dst + EXEC_SIZE);
+ }
pr_info("attempting bad execution at %p\n", func);
func();
}
@@ -551,25 +558,28 @@ static void lkdtm_do_action(enum ctype which)
schedule();
break;
case CT_EXEC_DATA:
- execute_location(data_area);
+ execute_location(data_area, true);
break;
case CT_EXEC_STACK: {
u8 stack_area[EXEC_SIZE];
- execute_location(stack_area);
+ execute_location(stack_area, true);
break;
}
case CT_EXEC_KMALLOC: {
u32 *kmalloc_area = kmalloc(EXEC_SIZE, GFP_KERNEL);
- execute_location(kmalloc_area);
+ execute_location(kmalloc_area, true);
kfree(kmalloc_area);
break;
}
case CT_EXEC_VMALLOC: {
u32 *vmalloc_area = vmalloc(EXEC_SIZE);
- execute_location(vmalloc_area);
+ execute_location(vmalloc_area, true);
vfree(vmalloc_area);
break;
}
+ case CT_EXEC_RODATA:
+ execute_location(lkdtm_rodata_do_nothing, false);
+ break;
case CT_EXEC_USERSPACE: {
unsigned long user_addr;
diff --git a/drivers/misc/lkdtm_rodata.c b/drivers/misc/lkdtm_rodata.c
new file mode 100644
index 000000000000..4d0d851f02b9
--- /dev/null
+++ b/drivers/misc/lkdtm_rodata.c
@@ -0,0 +1,10 @@
+/*
+ * This includes functions that are meant to live entirely in .rodata
+ * (via objcopy tricks), to validate the non-executability of .rodata.
+ */
+#include <linux/kernel.h>
+
+void lkdtm_rodata_do_nothing(void)
+{
+ /* Does nothing. We just want an architecture agnostic "return". */
+}
