linux-kernel - Re: [PATCH bpf-next 08/13] uprobes/x86: Add support to optimize uprobes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20241216101258.GA374@redhat.com>
Date: Mon, 16 Dec 2024 11:12:58 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: David Laight <David.Laight@...LAB.COM>
Cc: 'Jiri Olsa' <olsajiri@...il.com>, Peter Zijlstra <peterz@...radead.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	"bpf@...r.kernel.org" <bpf@...r.kernel.org>,
	Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	Hao Luo <haoluo@...gle.com>, Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Alan Maguire <alan.maguire@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-trace-kernel@...r.kernel.org" <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next 08/13] uprobes/x86: Add support to optimize
 uprobes

David,

let me say first that my understanding of this magic is very limited,
please correct me.

On 12/16, David Laight wrote:
>
> It all depends on how hard __replace_page() tries to be atomic.
> The page has to change from one backed by the executable to a private
> one backed by swap - otherwise you can't write to it.

This is what uprobe_write_opcode() does,

> But the problems arise when the instruction prefetch unit has read
> part of the 5-byte instruction (it might even only read half a cache
> line at a time).
> I'm not sure how long the pipeline can sit in that state - but I
> can do a memory read of a PCIe address that takes ~3000 clocks.
> (And a misaligned AVX-512 read is probably eight 8-byte transfers.)
>
> So I think you need to force an interrupt while the PTE is invalid.
> And that need to be simultaneous on all cpu running that process.

__replace_page() does ptep_get_and_clear(old_pte) + flush_tlb_page().

That's not enough?

> Stopping the process using ptrace would do it.

Not an option :/

Oleg.