linux-kernel - Re: [PATCH perf/core 03/22] uprobes: Move ref_ctr_offset update out of uprobe_write

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: <aA9dzY-2V3dCpMDq@krava>
Date: Mon, 28 Apr 2025 12:51:57 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
	Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	x86@...nel.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>,
	David Laight <David.Laight@...lab.com>,
	Thomas Weißschuh <thomas@...ch.de>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH perf/core 03/22] uprobes: Move ref_ctr_offset update out
 of uprobe_write_opcode

On Sun, Apr 27, 2025 at 04:13:35PM +0200, Oleg Nesterov wrote:
> On 04/21, Jiri Olsa wrote:
> >
> > +static int set_swbp_refctr(struct uprobe *uprobe, struct vm_area_struct *vma, unsigned long vaddr)
> > +{
> > +	struct mm_struct *mm = vma->vm_mm;
> > +	int err;
> > +
> > +	/* We are going to replace instruction, update ref_ctr. */
> > +	if (uprobe->ref_ctr_offset) {
> > +		err = update_ref_ctr(uprobe, mm, 1);
> > +		if (err)
> > +			return err;
> > +	}
> > +
> > +	err = set_swbp(&uprobe->arch, vma, vaddr);
> > +
> > +	/* Revert back reference counter if instruction update failed. */
> > +	if (err && uprobe->ref_ctr_offset)
> > +		update_ref_ctr(uprobe, mm, -1);
> > +	return err;
> >  }
> ...
> > +static int set_orig_refctr(struct uprobe *uprobe, struct vm_area_struct *vma, unsigned long vaddr)
> > +{
> > +	int err = set_orig_insn(&uprobe->arch, vma, vaddr);
> > +
> > +	/* Revert back reference counter even if instruction update failed. */
> > +	if (uprobe->ref_ctr_offset)
> > +		update_ref_ctr(uprobe, vma->vm_mm, -1);
> > +	return err;
> >  }
> 
> This doesn't look right even in the simplest case...
> 
> To simplify, suppose that uprobe_register() needs to change a single mm/vma
> and set_swbp() fails. In this case uprobe_register() calls uprobe_unregister()
> which will find the same vma and call set_orig_refctr(). set_orig_insn() will
> do nothing. But update_ref_ctr(uprobe, vma->vm_mm, -1) is wrong/unbalanced.
> 
> The current code updates ref_ctr after the verify_opcode() check, so it doesn't
> have this problem.

ah right :-\

could set_swbp/set_orig_insn return > 0 in case the memory was actually updated?
and we would update the refctr based on that, like:

+static int set_swbp_refctr(struct uprobe *uprobe, struct vm_area_struct *vma, unsigned long vaddr)
+{
+       struct mm_struct *mm = vma->vm_mm;
+       int err;
+
+       err = set_swbp(&uprobe->arch, vma, vaddr);
+       if (err > 0 && uprobe->ref_ctr_offset)
+               update_ref_ctr(uprobe, mm, 1);
+       return err;
+}

+static int set_orig_refctr(struct uprobe *uprobe, struct vm_area_struct *vma, unsigned long vaddr)
+{
+       int err = set_orig_insn(&uprobe->arch, vma, vaddr);
+
+       /* Revert back reference counter even if instruction update failed. */
+       if (err > 0 && uprobe->ref_ctr_offset)
+               update_ref_ctr(uprobe, vma->vm_mm, -1);
+       return err;
+}

but then what if update_ref_ctr fails..

> 
> -------------------------------------------------------------------------------
> OTOH, I think that the current logic is not really correct too,
> 
> 	/* Revert back reference counter if instruction update failed. */
> 	if (ret < 0 && is_register && ref_ctr_updated)
> 		update_ref_ctr(uprobe, mm, -1);
> 
> I think that "Revert back reference counter" logic should not depend on
> is_register. Otherwise we can have the unbalanced update_ref_ctr(-1) if
> uprobe_unregister() fails, then another uprobe_register() comes at the
> same address, and after that uprobe_unregister() succeeds.

sounds good to me

jirka