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Message-ID: <56C51574.80304@redhat.com>
Date: Wed, 17 Feb 2016 16:51:00 -0800
From: Laura Abbott <labbott@...hat.com>
To: Kees Cook <keescook@...omium.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jeremy Linton <jeremy.linton@....com>, Arnd Bergmann <arnd@...db.de>,
Mark Rutland <mark.rutland@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
kernel-hardening@...ts.openwall.com,
LKML <linux-kernel@...r.kernel.org>, PaX Team <pageexec@...email.hu>
Subject: Re: [PATCH v2] lkdtm: add test for executing .rodata
On 02/17/2016 01:22 PM, Kees Cook wrote:
> Make sure that the read-only data section isn't executable. To avoid
> making per-architecture assembly functions, just mark the new function
> as living in the .rodata section and force the flags (which requires
> adding a comment to hide the generated flags from the assembler).
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> v2:
> - fix the section bits hack to be more friendly
This is producing different assembler errors:
CC drivers/misc/lkdtm.o
/tmp/ccAJjNlS.s: Assembler messages:
/tmp/ccAJjNlS.s: Error: unaligned opcodes detected in executable segment
scripts/Makefile.build:258: recipe for target 'drivers/misc/lkdtm.o' failed
Doesn't seem to be toolchain dependent as I see it with two different ones
$ /opt/gcc-linaro-5.1-2015.08-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-as --version
GNU assembler (GNU Binutils) 2.25.0 Linaro 2015.10
$ aarch64-linux-gnu-as --version
GNU assembler version 2.26.20160125
The latter is the toolchain from Fedora 23.
Sticking an extra align directive in there doesn't seem to help.
Playing around a bit, this works if I don't have debuginfo turned on.
Possible gcc issue where something is not being calculated correctly
or gcc working as intended?
Thanks,
Laura
> ---
> drivers/misc/lkdtm.c | 28 +++++++++++++++++++++-------
> 1 file changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c
> index 11fdadc68e53..b15d08ff71a9 100644
> --- a/drivers/misc/lkdtm.c
> +++ b/drivers/misc/lkdtm.c
> @@ -100,6 +100,7 @@ enum ctype {
> CT_EXEC_STACK,
> CT_EXEC_KMALLOC,
> CT_EXEC_VMALLOC,
> + CT_EXEC_RODATA,
> CT_EXEC_USERSPACE,
> CT_ACCESS_USERSPACE,
> CT_WRITE_RO,
> @@ -137,6 +138,7 @@ static char* cp_type[] = {
> "EXEC_STACK",
> "EXEC_KMALLOC",
> "EXEC_VMALLOC",
> + "EXEC_RODATA",
> "EXEC_USERSPACE",
> "ACCESS_USERSPACE",
> "WRITE_RO",
> @@ -315,6 +317,12 @@ static int recursive_loop(int remaining)
> return recursive_loop(remaining - 1);
> }
>
> +static void __attribute__((__section__(".rodata,\"a\",\%progbits;//")))
> +do_nothing_rodata(void)
> +{
> + return;
> +}
> +
> static void do_nothing(void)
> {
> return;
> @@ -335,15 +343,18 @@ static noinline void corrupt_stack(void)
> memset((void *)data, 0, 64);
> }
>
> -static void execute_location(void *dst)
> +static 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();
> }
> @@ -438,25 +449,28 @@ 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(do_nothing_rodata, false);
> + break;
> case CT_EXEC_USERSPACE: {
> unsigned long user_addr;
>
>
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