[PATCH v2 3/3] arm: Add support for function error injection

[Leo Yan]

Hi Russell,

On Tue, Aug 06, 2019 at 06:00:15PM +0800, Leo Yan wrote:
> This patch implements arm specific functions regs_set_return_value() and
> override_function_with_return() to support function error injection.
> 
> In the exception flow, it updates pt_regs::ARM_pc with pt_regs::ARM_lr
> so can override the probed function return.

Gentle ping ...  Could you review this patch?

Thanks,
Leo.

> Signed-off-by: Leo Yan <leo.yan at linaro.org>
> ---
>  arch/arm/Kconfig              |  1 +
>  arch/arm/include/asm/ptrace.h |  5 +++++
>  arch/arm/lib/Makefile         |  2 ++
>  arch/arm/lib/error-inject.c   | 19 +++++++++++++++++++
>  4 files changed, 27 insertions(+)
>  create mode 100644 arch/arm/lib/error-inject.c
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 33b00579beff..2d3d44a037f6 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -77,6 +77,7 @@ config ARM
>  	select HAVE_EXIT_THREAD
>  	select HAVE_FAST_GUP if ARM_LPAE
>  	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
> +	select HAVE_FUNCTION_ERROR_INJECTION if !THUMB2_KERNEL
>  	select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG
>  	select HAVE_FUNCTION_TRACER if !XIP_KERNEL
>  	select HAVE_GCC_PLUGINS
> diff --git a/arch/arm/include/asm/ptrace.h b/arch/arm/include/asm/ptrace.h
> index 91d6b7856be4..3b41f37b361a 100644
> --- a/arch/arm/include/asm/ptrace.h
> +++ b/arch/arm/include/asm/ptrace.h
> @@ -89,6 +89,11 @@ static inline long regs_return_value(struct pt_regs *regs)
>  	return regs->ARM_r0;
>  }
>  
> +static inline void regs_set_return_value(struct pt_regs *regs, unsigned long rc)
> +{
> +	regs->ARM_r0 = rc;
> +}
> +
>  #define instruction_pointer(regs)	(regs)->ARM_pc
>  
>  #ifdef CONFIG_THUMB2_KERNEL
> diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
> index b25c54585048..8f56484a7156 100644
> --- a/arch/arm/lib/Makefile
> +++ b/arch/arm/lib/Makefile
> @@ -42,3 +42,5 @@ ifeq ($(CONFIG_KERNEL_MODE_NEON),y)
>    CFLAGS_xor-neon.o		+= $(NEON_FLAGS)
>    obj-$(CONFIG_XOR_BLOCKS)	+= xor-neon.o
>  endif
> +
> +obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
> diff --git a/arch/arm/lib/error-inject.c b/arch/arm/lib/error-inject.c
> new file mode 100644
> index 000000000000..2d696dc94893
> --- /dev/null
> +++ b/arch/arm/lib/error-inject.c
> @@ -0,0 +1,19 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/error-injection.h>
> +#include <linux/kprobes.h>
> +
> +void override_function_with_return(struct pt_regs *regs)
> +{
> +	/*
> +	 * 'regs' represents the state on entry of a predefined function in
> +	 * the kernel/module and which is captured on a kprobe.
> +	 *
> +	 * 'regs->ARM_lr' contains the the link register for the probed
> +	 * function, when kprobe returns back from exception it will override
> +	 * the end of probed function and directly return to the predefined
> +	 * function's caller.
> +	 */
> +	instruction_pointer_set(regs, regs->ARM_lr);
> +}
> +NOKPROBE_SYMBOL(override_function_with_return);
> -- 
> 2.17.1
>