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 <keesc...@chromium.org> --- 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". */ +}