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

Thomas Gleixner
2019-04-19T19:03:30Z

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