linux-kernel - Re: [PATCH] x86/mpx: fix recursive munmap() corruption

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Date:   Fri, 19 Apr 2019 12:55:36 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
cc:     LKML <linux-kernel@...r.kernel.org>, rguenther@...e.de,
        mhocko@...e.com, vbabka@...e.cz, luto@...capital.net,
        x86@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm@...ck.org, stable@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH] x86/mpx: fix recursive munmap() corruption

On Mon, 1 Apr 2019, Dave Hansen wrote:
> diff -puN mm/mmap.c~mpx-rss-pass-no-vma mm/mmap.c
> --- a/mm/mmap.c~mpx-rss-pass-no-vma	2019-04-01 06:56:53.409411123 -0700
> +++ b/mm/mmap.c	2019-04-01 06:56:53.423411123 -0700
> @@ -2731,9 +2731,17 @@ int __do_munmap(struct mm_struct *mm, un
>  		return -EINVAL;
>  
>  	len = PAGE_ALIGN(len);
> +	end = start + len;
>  	if (len == 0)
>  		return -EINVAL;
>  
> +	/*
> +	 * arch_unmap() might do unmaps itself.  It must be called
> +	 * and finish any rbtree manipulation before this code
> +	 * runs and also starts to manipulate the rbtree.
> +	 */
> +	arch_unmap(mm, start, end);

...
  
> -static inline void arch_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
> -			      unsigned long start, unsigned long end)
> +static inline void arch_unmap(struct mm_struct *mm, unsigned long start,
> +			      unsigned long end)

While you fixed up the asm-generic thing, this breaks arch/um and
arch/unicorn32. For those the fixup is trivial by removing the vma
argument.

But itt also breaks powerpc and there I'm not sure whether moving
arch_unmap() to the beginning of __do_munmap() is safe. Micheal???

Aside of that the powerpc variant looks suspicious:

static inline void arch_unmap(struct mm_struct *mm,
                              unsigned long start, unsigned long end)
{
 	if (start <= mm->context.vdso_base && mm->context.vdso_base < end)
                mm->context.vdso_base = 0;
}

Shouldn't that be: 

 	if (start >= mm->context.vdso_base && mm->context.vdso_base < end)

Hmm?

Thanks,

	tglx