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Date:   Tue, 13 Mar 2018 16:45:09 -0700
From:   Omar Sandoval <osandov@...ndov.com>
To:     Howard McLauchlan <hmclauchlan@...com>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Al Viro <viro@...iv.linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yonghong Song <yhs@...com>,
        "David S . Miller" <davem@...emloft.net>,
        Thomas Garnier <thgarnie@...gle.com>, kernel-team@...com,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, Josef Bacik <jbacik@...com>,
        Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH] bpf: whitelist syscalls for error injection

On Tue, Mar 13, 2018 at 04:16:27PM -0700, Howard McLauchlan wrote:
> Error injection is a useful mechanism to fail arbitrary kernel
> functions. However, it is often hard to guarantee an error propagates
> appropriately to user space programs. By injecting into syscalls, we can
> return arbitrary values to user space directly; this increases
> flexibility and robustness in testing, allowing us to test user space
> error paths effectively.
> 
> The following script, for example, fails calls to sys_open() from a
> given pid:
> 
> from bcc import BPF
> from sys import argv
> 
> pid = argv[1]
> 
> prog = r"""
> 
> int kprobe__SyS_open(struct pt_regs *ctx, const char *pathname, int flags)
> {
>     u32 pid = bpf_get_current_pid_tgid();
>     if (pid == %s)
>         bpf_override_return(ctx, -ENOENT);
>     return 0;
> }
> """ % pid
> 
> b = BPF(text = prog)
> while 1:
>     b.perf_buffer_poll()
> 
> This patch whitelists all syscalls defined with SYSCALL_DEFINE for error
> injection.
> 
> Signed-off-by: Howard McLauchlan <hmclauchlan@...com>
> ---
> based on 4.16-rc5
>  include/linux/syscalls.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index a78186d826d7..e8c6d63ace78 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -191,6 +191,8 @@ static inline int is_syscall_trace_event(struct trace_event_call *tp_event)
>  
>  #define SYSCALL_DEFINE0(sname)					\
>  	SYSCALL_METADATA(_##sname, 0);				\
> +	asmlinkage long sys_##sname(void);			\
> +	ALLOW_ERROR_INJECTION(sys_##sname, ERRNO);		\
>  	asmlinkage long sys_##sname(void)
>  
>  #define SYSCALL_DEFINE1(name, ...) SYSCALL_DEFINEx(1, _##name, __VA_ARGS__)
> @@ -210,6 +212,7 @@ static inline int is_syscall_trace_event(struct trace_event_call *tp_event)
>  #define __SYSCALL_DEFINEx(x, name, ...)					\
>  	asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))	\
>  		__attribute__((alias(__stringify(SyS##name))));		\
> +	ALLOW_ERROR_INJECTION(sys##name, ERRNO);			\
>  	static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__));	\
>  	asmlinkage long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__));	\
>  	asmlinkage long SyS##name(__MAP(x,__SC_LONG,__VA_ARGS__))	\
> -- 
> 2.14.1
> 

Adding a few more people to Cc

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