linux-kernel - Re: [PATCH] uprobes: use vm_special

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Message-ID: <20240911094401.GA19080@redhat.com>
Date: Wed, 11 Sep 2024 11:44:25 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Sven Schnelle <svens@...ux.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc: Michael Ellerman <mpe@...erman.id.au>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH] uprobes: use vm_special_mapping close() functionality

On 09/03, Sven Schnelle wrote:
>
> +static void uprobe_clear_state(const struct vm_special_mapping *sm, struct vm_area_struct *vma)
> +{
> +	struct xol_area *area = container_of(vma->vm_private_data, struct xol_area, xol_mapping);
> +
> +	mutex_lock(&delayed_uprobe_lock);
> +	delayed_uprobe_remove(NULL, vma->vm_mm);
> +	mutex_unlock(&delayed_uprobe_lock);
> +
> +	if (!area)
> +		return;
> +
> +	put_page(area->pages[0]);
> +	kfree(area->bitmap);
> +	kfree(area);
> +}
> +
>  static struct xol_area *__create_xol_area(unsigned long vaddr)
>  {
>  	struct mm_struct *mm = current->mm;
> @@ -1481,6 +1500,7 @@ static struct xol_area *__create_xol_area(unsigned long vaddr)
>
>  	area->xol_mapping.name = "[uprobes]";
>  	area->xol_mapping.fault = NULL;
> +	area->xol_mapping.close = uprobe_clear_state;

Ah, no, we can't do this :/

A malicious application can munmap() its "[uprobes]" vma and free
area/pages/bitmap. If this application hits the uprobe breakpoint after
that it will use the freed memory.

And no, "mm->uprobes_state.xol_area = NULL" in uprobe_clear_state() won't
help. Say, another thread can sleep on area.wq when munmap() is called.

Sorry, I should have realized that immediately, but I didn't :/

Andrew, this is uprobes-use-vm_special_mapping-close-functionality.patch
in mm-stable

Oleg.