linux-kernel - Re: [PATCH] bpf: whitelist syscalls for error injection

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Message-ID: <f47e1374-43eb-d7c6-dd0a-5d530ff2b4e2@fb.com>
Date:   Fri, 16 Mar 2018 15:55:04 -0700
From:   Howard McLauchlan <hmclauchlan@...com>
To:     Dominik Brodowski <linux@...inikbrodowski.net>
CC:     Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux API <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 <kernel-team@...com>
Subject: Re: [PATCH] bpf: whitelist syscalls for error injection

On 03/13/2018 04:56 PM, Andy Lutomirski wrote:
> On Tue, Mar 13, 2018 at 11:16 PM, Howard McLauchlan <hmclauchlan@...com> 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.
> 
> Temporary NAK IMO.  Specifically:
> 
>> 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);              \
> 
> sys_xyz() is not just the syscall itself; it's also a helper that's
> used for entirely silly reasons by various bits of kernel code for
> quite a few syscalls.  Fortunately, Dominik has patches to fix that,
> and Linus is even considering pulling them for 4.16.  This patch will
> most likely conflict with the final result of Dominik's series.
> 
> Can you and Dominik coordinate a bit to get this patch or its
> equivalent landed on top of Dominik's work?  It might make sense for
> Dominik to just add this patch to his series so it can land with the
> rest of it.  Dominik, Ingo, what do you think?
> 
> --Andy
> 

Dominik, 

This patch applies cleanly on top of your patch series. Is there anything you'd need from me to get this in on top of your work? 

Howard