linux-kernel - Re: [PATCH v2 8/8] jump_table: move entries into ro_after

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Date:   Tue, 3 Jul 2018 09:50:13 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-arch@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Kees Cook <keescook@...omium.org>,
        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>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 8/8] jump_table: move entries into ro_after_init region

+++ Ard Biesheuvel [02/07/18 20:11 +0200]:
>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>

For module parts:

Acked-by: Jessica Yu <jeyu@...nel.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
>