linux-kernel - Re: [RFC PATCH for 4.21 06/16] cpu_opv: Provide cpu

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Date:   Tue, 16 Oct 2018 17:10:29 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
        Ben Maurer <bmaurer@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [RFC PATCH for 4.21 06/16] cpu_opv: Provide cpu_opv system call
 (v8)

Hi Mathieu,

On (10/10/18 15:19), Mathieu Desnoyers wrote:
[..]
> +SYSCALL_DEFINE4(cpu_opv, struct cpu_op __user *, ucpuopv, int, cpuopcnt,
> +		int, cpu, int, flags)
> +{
[..]
> +again:
> +	ret = cpu_opv_pin_pages(cpuopv, cpuopcnt, &vaddr_ptrs);
> +	if (ret)
> +		goto end;
> +	ret = do_cpu_opv(cpuopv, cpuopcnt, &vaddr_ptrs, cpu);
> +	if (ret == -EAGAIN)
> +		retry = true;
> +end:
> +	for (i = 0; i < vaddr_ptrs.nr_vaddr; i++) {
> +		struct vaddr *vaddr = &vaddr_ptrs.addr[i];
> +		int j;
> +
> +		vm_unmap_user_ram((void *)vaddr->mem, vaddr->nr_pages);

A dumb question.

Both vm_unmap_user_ram() and vm_map_user_ram() can BUG_ON().
So this is
   userspace -> syscall -> cpu_opv() -> vm_unmap_user_ram() -> BUG_ON()

Any chance someone can exploit it?

	-ss