From: Oleg Nesterov <oleg@redhat.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
"David S. Miller" <davem@davemloft.net>, X86 ML <x86@kernel.org>,
Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: Why do kprobes and uprobes singlestep?
Date: Mon, 1 Mar 2021 17:51:31 +0100 [thread overview]
Message-ID: <20210301165130.GA5351@redhat.com> (raw)
In-Reply-To: <CALCETrXzXv-V3A3SpN_Pdj_PNG8Gw0AVsZD7+VO-q_xCAu2T2A@mail.gmail.com>
Hi Andy,
sorry for delay.
On 02/23, Andy Lutomirski wrote:
>
> A while back, I let myself be convinced that kprobes genuinely need to
> single-step the kernel on occasion, and I decided that this sucked but
> I could live with it. it would, however, be Really Really Nice (tm)
> if we could have a rule that anyone running x86 Linux who single-steps
> the kernel (e.g. kgdb and nothing else) gets to keep all the pieces
> when the system falls apart around them. Specifically, if we don't
> allow kernel single-stepping and if we suitably limit kernel
> instruction breakpoints (the latter isn't actually a major problem),
> then we don't really really need to use IRET to return to the kernel,
> and that means we can avoid some massive NMI nastiness.
Not sure I understand you correctly, I know almost nothing about low-level
x86 magic.
But I guess this has nothing to do with uprobes, they do not single-step
in kernel mode, right?
> Uprobes seem to single-step user code for no discernable reason.
> (They want to trap after executing an out of line instruction, AFAICT.
> Surely INT3 or even CALL after the out-of-line insn would work as well
> or better.)
Uprobes use single-step from the very beginning, probably because this
is the most simple and "standard" way to implement xol.
And please note that CALL/JMP/etc emulation was added much later to fix the
problems with non-canonical addresses, and this emulation it still incomplete.
Oleg.
next prev parent reply other threads:[~2021-03-01 19:30 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-23 23:24 Why do kprobes and uprobes singlestep? Andy Lutomirski
2021-02-24 1:17 ` Masami Hiramatsu
2021-02-24 19:45 ` Andy Lutomirski
2021-02-25 2:22 ` Masami Hiramatsu
2021-02-25 6:03 ` Andy Lutomirski
2021-02-25 9:11 ` Masami Hiramatsu
2021-03-01 14:08 ` [RFC PATCH 0/1] x86/kprobes: Remoev single-step trap from x86 kprobes Masami Hiramatsu
2021-03-01 14:08 ` [RFC PATCH 1/1] x86/kprobes: Use int3 instead of debug trap for single-step Masami Hiramatsu
2021-03-02 8:06 ` Peter Zijlstra
2021-03-02 8:38 ` Peter Zijlstra
2021-03-02 8:41 ` Peter Zijlstra
2021-03-02 8:54 ` Peter Zijlstra
2021-03-02 12:51 ` Masami Hiramatsu
2021-03-02 13:58 ` Peter Zijlstra
2021-03-02 15:25 ` [PATCH -tip 0/3] x86/kprobes: Remoev single-step trap from x86 kprobes Masami Hiramatsu
2021-03-02 15:25 ` [PATCH -tip 1/3] x86/kprobes: Retrieve correct opcode for group instruction Masami Hiramatsu
2021-03-23 15:15 ` [tip: x86/core] " tip-bot2 for Masami Hiramatsu
2021-03-02 15:25 ` [PATCH -tip 2/3] x86/kprobes: Identify far indirect JMP correctly Masami Hiramatsu
2021-03-23 15:15 ` [tip: x86/core] " tip-bot2 for Masami Hiramatsu
2021-03-02 15:25 ` [PATCH -tip 3/3] x86/kprobes: Use int3 instead of debug trap for single-step Masami Hiramatsu
2021-03-23 15:15 ` [tip: x86/core] " tip-bot2 for Masami Hiramatsu
2021-03-17 14:55 ` [PATCH -tip 0/3] x86/kprobes: Remoev single-step trap from x86 kprobes Masami Hiramatsu
2021-03-17 16:26 ` Peter Zijlstra
2021-03-17 17:45 ` Andy Lutomirski
2021-02-25 9:59 ` Why do kprobes and uprobes singlestep? Peter Zijlstra
2021-03-01 16:51 ` Oleg Nesterov [this message]
2021-03-02 1:36 ` Andy Lutomirski
2021-03-02 20:24 ` Alexei Starovoitov
2021-03-02 21:02 ` Andy Lutomirski
2021-03-03 1:22 ` Alexei Starovoitov
2021-03-03 1:46 ` Andy Lutomirski
2021-03-03 2:18 ` Alexei Starovoitov
2021-03-03 13:27 ` Oleg Nesterov
2021-03-03 18:11 ` Daniel Xu
2021-03-03 19:14 ` Andy Lutomirski
2021-03-02 20:25 ` Oleg Nesterov
2021-03-02 20:35 ` Andy Lutomirski
2021-03-02 20:28 ` Oleg Nesterov
2021-03-02 2:22 ` Masami Hiramatsu
2021-03-02 2:48 ` Andy Lutomirski
2021-03-02 20:31 ` Oleg Nesterov
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