linux-kernel - Re: [PATCH 8/8] riscv: add two hook functions of ftrace

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 04 Mar 2020 17:44:19 -0800 (PST)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     zong.li@...ive.com
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        zong.li@...ive.com
Subject:     Re: [PATCH 8/8] riscv: add two hook functions of ftrace

On Mon, 17 Feb 2020 00:32:23 PST (-0800), zong.li@...ive.com wrote:
> After the text section be mask as non-writable, the ftrace have to
> change the permission of text for dynamic patching the intructions.
> Add ftrace_arch_code_modify_prepare and
> ftrace_arch_code_modify_post_process to change permission.
>
> Signed-off-by: Zong Li <zong.li@...ive.com>
> ---
>  arch/riscv/kernel/ftrace.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
>
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> index c40fdcdeb950..576df0807200 100644
> --- a/arch/riscv/kernel/ftrace.c
> +++ b/arch/riscv/kernel/ftrace.c
> @@ -7,9 +7,27 @@
>
>  #include <linux/ftrace.h>
>  #include <linux/uaccess.h>
> +#include <linux/memory.h>
> +#include <asm/set_memory.h>
>  #include <asm/cacheflush.h>
>
>  #ifdef CONFIG_DYNAMIC_FTRACE
> +int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex)
> +{
> +	mutex_lock(&text_mutex);
> +	set_kernel_text_rw();
> +	set_all_modules_text_rw();
> +	return 0;
> +}

None of the other architectures are doing anything remotely like this in these
functions, despite many supporting STRICT_KERNEL_RWX.  Having a function that
maps all text as RW seems super dangerous, as one stack attack means NX is
gone.

Looks like FIX_TEXT_POKE0 is the magic that makes the other ports work.

> +
> +int ftrace_arch_code_modify_post_process(void) __releases(&text_mutex)
> +{
> +	set_all_modules_text_ro();
> +	set_kernel_text_ro();
> +	mutex_unlock(&text_mutex);
> +	return 0;
> +}

Presumably this needs a icache flush as well?  Probably better to do so when
installing the instructions, though.

> +
>  static int ftrace_check_current_call(unsigned long hook_pos,
>  				     unsigned int *expected)
>  {