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Date: Thu, 23 Mar 2017 14:14:20 -0700
From: Kees Cook <keescook@...omium.org>
To: Eddie Kovsky <ewk@...ovsky.org>
Cc: Jessica Yu <jeyu@...hat.com>, Rusty Russell <rusty@...tcorp.com.au>,
LKML <linux-kernel@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH v3 2/2] extable: verify address is read-only
On Wed, Mar 22, 2017 at 7:55 PM, Eddie Kovsky <ewk@...ovsky.org> wrote:
> Provide a mechanism to check if the address of a variable is
> const or ro_after_init. It mimics the existing functions that test if an
> address is inside the kernel's text section.
>
> Other functions inside the kernel could then use this capability to
> verify that their arguments are read-only.
>
> Signed-off-by: Eddie Kovsky <ewk@...ovsky.org>
Looks great!
Acked-by: Kees Cook <keescook@...omium.org>
-Kees
> ---
> Changes in v3:
> - Fix missing declaration of is_module_rodata_address()
>
> include/linux/kernel.h | 2 ++
> kernel/extable.c | 29 +++++++++++++++++++++++++++++
> 2 files changed, 31 insertions(+)
>
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 4c26dc3a8295..51beea39e6c4 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -444,6 +444,8 @@ extern int core_kernel_data(unsigned long addr);
> extern int __kernel_text_address(unsigned long addr);
> extern int kernel_text_address(unsigned long addr);
> extern int func_ptr_is_kernel_text(void *ptr);
> +extern int core_kernel_ro_data(unsigned long addr);
> +extern int kernel_ro_address(unsigned long addr);
>
> unsigned long int_sqrt(unsigned long);
>
> diff --git a/kernel/extable.c b/kernel/extable.c
> index 2676d7f8baf6..3c3a9f4e6250 100644
> --- a/kernel/extable.c
> +++ b/kernel/extable.c
> @@ -154,3 +154,32 @@ int func_ptr_is_kernel_text(void *ptr)
> return 1;
> return is_module_text_address(addr);
> }
> +
> +/**
> + * core_kernel_ro_data - Verify address points to read-only section
> + * @addr: address to test
> + *
> + */
> +int core_kernel_ro_data(unsigned long addr)
> +{
> + if (addr >= (unsigned long)__start_rodata &&
> + addr < (unsigned long)__end_rodata)
> + return 1;
> +
> + if (addr >= (unsigned long)__start_data_ro_after_init &&
> + addr < (unsigned long)__end_data_ro_after_init)
> + return 1;
> +
> + return 0;
> +}
> +
> +/* Verify that address is const or ro_after_init. */
> +int kernel_ro_address(unsigned long addr)
> +{
> + if (core_kernel_ro_data(addr))
> + return 1;
> + if (is_module_rodata_address(addr))
> + return 1;
> +
> + return 0;
> +}
> --
> 2.12.0
--
Kees Cook
Pixel Security
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