From: Gabriel Krisman Bertazi <krisman@collabora.com>
To: Florian Weimer <fw@deneb.enyo.de>
Cc: luto@kernel.org, tglx@linutronix.de, keescook@chromium.org,
christian.brauner@ubuntu.com, peterz@infradead.org,
willy@infradead.org, shuah@kernel.org,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
linux-kselftest@vger.kernel.org, x86@kernel.org,
gofmanp@gmail.com, kernel@collabora.com
Subject: Re: [PATCH v7 7/7] docs: Document Syscall User Dispatch
Date: Wed, 18 Nov 2020 12:02:36 -0500 [thread overview]
Message-ID: <877dqivbrn.fsf@collabora.com> (raw)
In-Reply-To: <875z63yrrq.fsf@mid.deneb.enyo.de> (Florian Weimer's message of "Wed, 18 Nov 2020 09:48:41 +0100")
Florian Weimer <fw@deneb.enyo.de> writes:
> * Gabriel Krisman Bertazi:
>
>> +Interface
>> +---------
>> +
>> +A process can setup this mechanism on supported kernels
>> +CONFIG_SYSCALL_USER_DISPATCH) by executing the following prctl:
>> +
>> + prctl(PR_SET_SYSCALL_USER_DISPATCH, <op>, <offset>, <length>, [selector])
>> +
>> +<op> is either PR_SYS_DISPATCH_ON or PR_SYS_DISPATCH_OFF, to enable and
>> +disable the mechanism globally for that thread. When
>> +PR_SYS_DISPATCH_OFF is used, the other fields must be zero.
>> +
>> +<offset> and <offset+length> delimit a closed memory region interval
>> +from which syscalls are always executed directly, regardless of the
>> +userspace selector. This provides a fast path for the C library, which
>> +includes the most common syscall dispatchers in the native code
>> +applications, and also provides a way for the signal handler to return
>> +without triggering a nested SIGSYS on (rt_)sigreturn. Users of this
>> +interface should make sure that at least the signal trampoline code is
>> +included in this region. In addition, for syscalls that implement the
>> +trampoline code on the vDSO, that trampoline is never intercepted.
>> +
>> +[selector] is a pointer to a char-sized region in the process memory
>> +region, that provides a quick way to enable disable syscall redirection
>> +thread-wide, without the need to invoke the kernel directly. selector
>> +can be set to PR_SYS_DISPATCH_ON or PR_SYS_DISPATCH_OFF. Any other
>> +value should terminate the program with a SIGSYS.
>
> Is this a process property or a task/thread property? The last
> paragraph says “thread-wide”, but the first paragraph says “process”.
It is per-thread, as it doesn't survive across clone/fork syscalls. I
will fix the first paragraph of this text.
--
Gabriel Krisman Bertazi
next prev parent reply other threads:[~2020-11-18 17:02 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-18 3:28 [PATCH v7 0/7] Syscall User Dispatch Gabriel Krisman Bertazi
2020-11-18 3:28 ` [PATCH v7 1/7] x86: vdso: Expose sigreturn address on vdso to the kernel Gabriel Krisman Bertazi
2020-11-18 3:28 ` [PATCH v7 2/7] signal: Expose SYS_USER_DISPATCH si_code type Gabriel Krisman Bertazi
2020-11-18 3:28 ` [PATCH v7 3/7] kernel: Implement selective syscall userspace redirection Gabriel Krisman Bertazi
2020-11-19 12:36 ` Peter Zijlstra
2020-11-19 17:43 ` Gabriel Krisman Bertazi
2020-11-21 0:18 ` Kees Cook
2020-11-22 4:01 ` Andy Lutomirski
2020-11-18 3:28 ` [PATCH v7 4/7] entry: Support Syscall User Dispatch on common syscall entry Gabriel Krisman Bertazi
2020-11-18 3:28 ` [PATCH v7 5/7] selftests: Add kselftest for syscall user dispatch Gabriel Krisman Bertazi
2020-11-18 3:28 ` [PATCH v7 6/7] selftests: Add benchmark " Gabriel Krisman Bertazi
2020-11-18 3:28 ` [PATCH v7 7/7] docs: Document Syscall User Dispatch Gabriel Krisman Bertazi
2020-11-18 8:48 ` Florian Weimer
2020-11-18 17:02 ` Gabriel Krisman Bertazi [this message]
2020-11-18 8:47 ` [PATCH v7 0/7] " Florian Weimer
2020-11-18 17:01 ` Gabriel Krisman Bertazi
2020-11-18 17:22 ` Florian Weimer
2020-11-19 12:38 ` Peter Zijlstra
2020-11-21 0:24 ` Kees Cook
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