Subject: Re: [PATCH] LoongArch: Add support for function error injection
To:     Huacai Chen <chenhuacai@kernel.org>,
        WANG Xuerui <kernel@xen0n.name>
References: <1678173001-16852-1-git-send-email-yangtiezhu@loongson.cn>
Cc:     loongarch@lists.linux.dev, linux-kernel@vger.kernel.org,
        loongson-kernel@lists.loongnix.cn,
        Masami Hiramatsu <mhiramat@kernel.org>
From:   Tiezhu Yang <yangtiezhu@loongson.cn>
Message-ID: <fb573603-edc1-9c87-5739-a33e5e1db6e1@loongson.cn>
Date:   Fri, 10 Mar 2023 10:07:09 +0800
User-Agent: Mozilla/5.0 (X11; Linux mips64; rv:45.0) Gecko/20100101
 Thunderbird/45.4.0
MIME-Version: 1.0
In-Reply-To: <1678173001-16852-1-git-send-email-yangtiezhu@loongson.cn>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

This feature is related with kprobes, add Masami to CC.

On 03/07/2023 03:10 PM, Tiezhu Yang wrote:
> Inspired by the commit 42d038c4fb00 ("arm64: Add support for function error
> injection") and commit ee55ff803b38 ("riscv: Add support for function error
> injection"), support function error injection for LoongArch.
>
> Mainly implement two functions:
> (1) regs_set_return_value() which is used to overwrite the return value,
> (2) override_function_with_return() which is used to override the probed
> function returning and jump to its caller.
>
> Here is a simple test under CONFIG_FUNCTION_ERROR_INJECTION and
> CONFIG_FAIL_FUNCTION:
>
>   # echo sys_clone > /sys/kernel/debug/fail_function/inject
>   # echo 100 > /sys/kernel/debug/fail_function/probability
>   # dmesg
>   bash: fork: Invalid argument
>   # dmesg
>   ...
>   FAULT_INJECTION: forcing a failure.
>   name fail_function, interval 1, probability 100, space 0, times 1
>   ...
>   Call Trace:
>   [<90000000002238f4>] show_stack+0x5c/0x180
>   [<90000000012e384c>] dump_stack_lvl+0x60/0x88
>   [<9000000000b1879c>] should_fail_ex+0x1b0/0x1f4
>   [<900000000032ead4>] fei_kprobe_handler+0x28/0x6c
>   [<9000000000230970>] kprobe_breakpoint_handler+0xf0/0x118
>   [<90000000012e3e60>] do_bp+0x2c4/0x358
>   [<9000000002241924>] exception_handlers+0x1924/0x10000
>   [<900000000023b7d0>] sys_clone+0x0/0x4
>   [<90000000012e4744>] do_syscall+0x7c/0x94
>   [<9000000000221e44>] handle_syscall+0xc4/0x160
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
> ---
>  arch/loongarch/Kconfig              |  1 +
>  arch/loongarch/include/asm/ptrace.h |  6 ++++++
>  arch/loongarch/lib/Makefile         |  2 ++
>  arch/loongarch/lib/error-inject.c   | 10 ++++++++++
>  4 files changed, 19 insertions(+)
>  create mode 100644 arch/loongarch/lib/error-inject.c
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index 7fd5125..b16ff7e 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -99,6 +99,7 @@ config LOONGARCH
>  	select HAVE_FAST_GUP
>  	select HAVE_FTRACE_MCOUNT_RECORD
>  	select HAVE_FUNCTION_ARG_ACCESS_API
> +	select HAVE_FUNCTION_ERROR_INJECTION
>  	select HAVE_FUNCTION_GRAPH_TRACER
>  	select HAVE_FUNCTION_TRACER
>  	select HAVE_GENERIC_VDSO
> diff --git a/arch/loongarch/include/asm/ptrace.h b/arch/loongarch/include/asm/ptrace.h
> index d761db9..db7332a 100644
> --- a/arch/loongarch/include/asm/ptrace.h
> +++ b/arch/loongarch/include/asm/ptrace.h
> @@ -154,6 +154,12 @@ static inline long regs_return_value(struct pt_regs *regs)
>  	return regs->regs[4];
>  }
>
> +static inline void regs_set_return_value(struct pt_regs *regs,
> +					 unsigned long val)
> +{
> +	regs->regs[4] = val;
> +}
> +
>  #define instruction_pointer(regs) ((regs)->csr_era)
>  #define profile_pc(regs) instruction_pointer(regs)
>
> diff --git a/arch/loongarch/lib/Makefile b/arch/loongarch/lib/Makefile
> index 40bde63..30b1595 100644
> --- a/arch/loongarch/lib/Makefile
> +++ b/arch/loongarch/lib/Makefile
> @@ -5,3 +5,5 @@
>
>  lib-y	+= delay.o memset.o memcpy.o memmove.o \
>  	   clear_user.o copy_user.o dump_tlb.o unaligned.o
> +
> +obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
> diff --git a/arch/loongarch/lib/error-inject.c b/arch/loongarch/lib/error-inject.c
> new file mode 100644
> index 0000000..afc9e1c
> --- /dev/null
> +++ b/arch/loongarch/lib/error-inject.c
> @@ -0,0 +1,10 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/error-injection.h>
> +#include <linux/kprobes.h>
> +
> +void override_function_with_return(struct pt_regs *regs)
> +{
> +	instruction_pointer_set(regs, regs->regs[1]);
> +}
> +NOKPROBE_SYMBOL(override_function_with_return);
>