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Date: Mon, 2 Jul 2018 11:29:55 -0700
From: Kees Cook <keescook@...omium.org>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
LKML <linux-kernel@...r.kernel.org>,
linux-s390 <linux-s390@...r.kernel.org>,
linux-arch <linux-arch@...r.kernel.org>,
Arnd Bergmann <arnd@...db.de>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Will Deacon <will.deacon@....com>,
Thomas Gleixner <tglx@...utronix.de>,
Catalin Marinas <catalin.marinas@....com>,
Ingo Molnar <mingo@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Jessica Yu <jeyu@...nel.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 8/8] jump_table: move entries into ro_after_init region
On Mon, Jul 2, 2018 at 11:11 AM, Ard Biesheuvel
<ard.biesheuvel@...aro.org> wrote:
> The __jump_table sections emitted into the core kernel and into
> each module consist of statically initialized references into
> other parts of the code, and with the exception of entries that
> point into init code, which are defused at post-init time, these
> data structures are never modified.
>
> So let's move them into the ro_after_init section, to prevent them
> from being corrupted inadvertently by buggy code, or deliberately
> by an attacker.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Yay more things read-only! :)
Reviewed-by: Kees Cook <keescook@...omium.org>
> ---
> arch/arm/kernel/vmlinux-xip.lds.S | 1 +
> arch/s390/kernel/vmlinux.lds.S | 1 +
> include/asm-generic/vmlinux.lds.h | 11 +++++++----
> kernel/module.c | 9 +++++++++
> 4 files changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm/kernel/vmlinux-xip.lds.S b/arch/arm/kernel/vmlinux-xip.lds.S
> index 3593d5c1acd2..763c41068ecc 100644
> --- a/arch/arm/kernel/vmlinux-xip.lds.S
> +++ b/arch/arm/kernel/vmlinux-xip.lds.S
> @@ -118,6 +118,7 @@ SECTIONS
> RW_DATA_SECTION(L1_CACHE_BYTES, PAGE_SIZE, THREAD_SIZE)
> .data.ro_after_init : AT(ADDR(.data.ro_after_init) - LOAD_OFFSET) {
> *(.data..ro_after_init)
> + JUMP_TABLE_DATA
> }
> _edata = .;
>
> diff --git a/arch/s390/kernel/vmlinux.lds.S b/arch/s390/kernel/vmlinux.lds.S
> index f0414f52817b..a7cf61e46f88 100644
> --- a/arch/s390/kernel/vmlinux.lds.S
> +++ b/arch/s390/kernel/vmlinux.lds.S
> @@ -67,6 +67,7 @@ SECTIONS
> __start_ro_after_init = .;
> .data..ro_after_init : {
> *(.data..ro_after_init)
> + JUMP_TABLE_DATA
> }
> EXCEPTION_TABLE(16)
> . = ALIGN(PAGE_SIZE);
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index e373e2e10f6a..ed6befa4c47b 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -256,10 +256,6 @@
> STRUCT_ALIGN(); \
> *(__tracepoints) \
> /* implement dynamic printk debug */ \
> - . = ALIGN(8); \
> - __start___jump_table = .; \
> - KEEP(*(__jump_table)) \
> - __stop___jump_table = .; \
> . = ALIGN(8); \
> __start___verbose = .; \
> KEEP(*(__verbose)) \
> @@ -303,6 +299,12 @@
> . = __start_init_task + THREAD_SIZE; \
> __end_init_task = .;
>
> +#define JUMP_TABLE_DATA \
> + . = ALIGN(8); \
> + __start___jump_table = .; \
> + KEEP(*(__jump_table)) \
> + __stop___jump_table = .;
> +
> /*
> * Allow architectures to handle ro_after_init data on their
> * own by defining an empty RO_AFTER_INIT_DATA.
> @@ -311,6 +313,7 @@
> #define RO_AFTER_INIT_DATA \
> __start_ro_after_init = .; \
> *(.data..ro_after_init) \
> + JUMP_TABLE_DATA \
> __end_ro_after_init = .;
> #endif
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 7cb82e0fcac0..0d4e320e41cd 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3349,6 +3349,15 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
> * Note: ro_after_init sections also have SHF_{WRITE,ALLOC} set.
> */
> ndx = find_sec(info, ".data..ro_after_init");
> + if (ndx)
> + info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT;
> + /*
> + * Mark the __jump_table section as ro_after_init as well: these data
> + * structures are never modified, with the exception of entries that
> + * refer to code in the __init section, which are annotated as such
> + * at module load time.
> + */
> + ndx = find_sec(info, "__jump_table");
> if (ndx)
> info->sechdrs[ndx].sh_flags |= SHF_RO_AFTER_INIT;
>
> --
> 2.17.1
>
--
Kees Cook
Pixel Security
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