linux-kernel - Re: [PATCH] mm/vmalloc: Sanitize __get_vm

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Message-ID: <20200403181818.GA5538@pc636>
Date:   Fri, 3 Apr 2020 20:18:18 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, jroedel@...e.de,
        vbabka@...e.cz, urezki@...il.com,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] mm/vmalloc: Sanitize __get_vm_area() arguments

On Fri, Apr 03, 2020 at 06:32:53PM +0200, Peter Zijlstra wrote:
> 
> __get_vm_area() is an exported symbol, make sure the callers stay in
> the expected memory range. When calling this function with memory
> ranges outside of the VMALLOC range *bad* things can happen.
> 
> (I noticed this when I managed to corrupt the kernel text by accident)
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  mm/vmalloc.c |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2130,6 +2130,13 @@ static struct vm_struct *__get_vm_area_n
>  struct vm_struct *__get_vm_area(unsigned long size, unsigned long flags,
>  				unsigned long start, unsigned long end)
>  {
> +	/*
> +	 * Ensure callers stay in the vmalloc range.
> +	 */
> +	if (WARN_ON(start < VMALLOC_START || start > VMALLOC_END ||
> +		    end < VMALLOC_START || end > VMALLOC_END))
> +		return NULL;
> +
>  	return __get_vm_area_node(size, 1, flags, start, end, NUMA_NO_NODE,
>  				  GFP_KERNEL, __builtin_return_address(0));
>  }
Peter, could you please clarify what kind of issues you had and how you
tested?

__get_vm_area() is not limited by allocating only with vmalloc space,
it can use whole virtual address space/range, i.e. 1 - ULONG_MAX.

Though, i am not sure if there are users(who uses __get_vm_area())
which allocate outside of vmalloc address space.

--
Vlad Rezki