From: Yuxuan Shui <yshuiv7@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Andy Lutomirski <luto@kernel.org>,
Gabriel Krisman Bertazi <krisman@collabora.com>,
open list <linux-kernel@vger.kernel.org>,
"Robert O'Callahan" <rocallahan@gmail.com>,
Kyle Huey <me@kylehuey.com>
Subject: Re: [REGRESSION] x86/entry: TIF_SINGLESTEP handling is still broken
Date: Sun, 31 Jan 2021 18:54:35 +0000 [thread overview]
Message-ID: <87v9bdc4yc.fsf@m5Zedd9JOGzJrf0> (raw)
In-Reply-To: <CAP045ApxLJ7vXOVp5Cwx7WEyDr6v01D9YD3xGFDv3WAp6czaMQ@mail.gmail.com>
I didn't understand Kyle's point at first, so I asked for clarification
and will record my understanding below for posterity.
ARCH_SYSCALL_EXIT_WORK was a flag that was checked by various functions
(via SYSCALL_EXIT_WORK) before calling syscall_exit_work, which is what
reports single steps. This flag was supposed to be overridden by
architecture specific definitions. And indeed, x86 overrides it, to
TIF_SINGLESTEP.
However, commit 2991552447707d791d9d81a5dc161f9e9e90b163 renamed
ARCH_SYSCALL_EXIT_WORK to ARCH_SYSCALL_WORK_EXIT, thus x86's definition
no longer override it. Looks like there was an oversight the definition
in x86 wasn't updated.
But renaming the definition in x86 is not enough, as TIF_SINGLESTEP is
set in current_thread_info()->flags, and the same commit has removed the
code that checks those flags. We have to also migrate TIF_SINGLESTEP from
thread info flags to syscall work flags, to make the whole thing work again.
next prev parent reply other threads:[~2021-01-31 20:25 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-31 1:32 [REGRESSION] x86/entry: TIF_SINGLESTEP handling is still broken Kyle Huey
2021-01-31 1:55 ` Linus Torvalds
2021-01-31 2:50 ` Kyle Huey
2021-01-31 18:54 ` Yuxuan Shui [this message]
2021-01-31 20:10 ` Linus Torvalds
2021-01-31 20:20 ` Gabriel Krisman Bertazi
2021-01-31 21:21 ` Linus Torvalds
2021-01-31 21:30 ` Linus Torvalds
2021-01-31 22:04 ` Andy Lutomirski
2021-01-31 22:08 ` Kyle Huey
2021-01-31 22:20 ` Andy Lutomirski
2021-01-31 22:27 ` Kyle Huey
2021-01-31 23:17 ` Kyle Huey
2021-01-31 23:35 ` Linus Torvalds
2021-01-31 23:55 ` Linus Torvalds
2021-02-03 18:00 ` [PATCH] entry: Fix missed trap after single-step on system call return Gabriel Krisman Bertazi
2021-02-03 18:10 ` Linus Torvalds
2021-02-03 18:18 ` Andy Lutomirski
2021-02-03 18:22 ` Linus Torvalds
2021-02-03 18:11 ` Kyle Huey
2021-02-03 23:55 ` Kyle Huey
2021-02-04 17:46 ` Linus Torvalds
2021-02-05 23:24 ` [tip: core/urgent] entry: Ensure " tip-bot2 for Gabriel Krisman Bertazi
2021-01-31 22:57 ` [REGRESSION] x86/entry: TIF_SINGLESTEP handling is still broken Linus Torvalds
2021-01-31 23:36 ` Andy Lutomirski
2021-01-31 23:39 ` Kyle Huey
2021-01-31 23:40 ` Andy Lutomirski
2021-02-01 2:25 ` Robert O'Callahan
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