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Date: Tue, 7 Jun 2016 18:02:01 -0700
From: Laura Abbott <labbott@...hat.com>
To: Kees Cook <keescook@...omium.org>, kernel-hardening@...ts.openwall.com
Cc: Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
"David S. Miller" <davem@...emloft.net>,
Mauro Carvalho Chehab <mchehab@....samsung.com>, Jiri Slaby
<jslaby@...e.cz>, Guenter Roeck <linux@...ck-us.net>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] lkdtm: add function for testing .rodata section
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 <keescook@...omium.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". */
> +}
>
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