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Date:   Mon, 13 Mar 2023 11:24:28 +0800
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Subject: Re: [PATCH] LoongArch: Add support for function error injection
To:     Tiezhu Yang <yangtiezhu@loongson.cn>,
        Huacai Chen <chenhuacai@kernel.org>,
        WANG Xuerui <kernel@xen0n.name>
Cc:     loongarch@lists.linux.dev, linux-kernel@vger.kernel.org,
        loongson-kernel@lists.loongnix.cn,
        Masami Hiramatsu <mhiramat@kernel.org>
References: <1678173001-16852-1-git-send-email-yangtiezhu@loongson.cn>
 <fb573603-edc1-9c87-5739-a33e5e1db6e1@loongson.cn>
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From:   Hengqi Chen <chenhengqi@outlook.com>
In-Reply-To: <fb573603-edc1-9c87-5739-a33e5e1db6e1@loongson.cn>
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On 2023/3/10 10:07, Tiezhu Yang wrote:
> 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);
>>
> 
> 

Tested-by: Hengqi Chen <hengqi.chen@gmail.com>