Date:   Sat, 11 Mar 2023 00:22:21 +0900
From:   Masami Hiramatsu (Google) <mhiramat@kernel.org>
To:     Tiezhu Yang <yangtiezhu@loongson.cn>
Cc:     Huacai Chen <chenhuacai@kernel.org>,
        WANG Xuerui <kernel@xen0n.name>, loongarch@lists.linux.dev,
        linux-kernel@vger.kernel.org, loongson-kernel@lists.loongnix.cn,
        Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH] LoongArch: Add support for function error injection
Message-Id: <20230311002221.721ef2d91e7defb65dd77b36@kernel.org>
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        <fb573603-edc1-9c87-5739-a33e5e1db6e1@loongson.cn>
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On Fri, 10 Mar 2023 10:07:09 +0800
Tiezhu Yang <yangtiezhu@loongson.cn> 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>

Thanks for porting! This looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thanks!

> > ---
> >  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);
> >
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>