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Le 23/04/2019 à 15:34, Thomas Gleixner a écrit :
On Tue, 23 Apr 2019, Laurent Dufour wrote:
Le 20/04/2019 à 12:31, Michael Ellerman a écrit :
Thomas Gleixner <tglx@xxxxxxxxxxxxx> writes:
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?

Yeah looks pretty suspicious. I'll follow-up with Laurent who wrote it.
Thanks for spotting it!

I've to admit that I had to read that code carefully before answering.

There are 2 assumptions here:
  1. 'start' and 'end' are page aligned (this is guaranteed by __do_munmap().
  2. the VDSO is 1 page (this is guaranteed by the union vdso_data_store on
powerpc).

The idea is to handle a munmap() call surrounding the VDSO area:
       | VDSO |
  ^start         ^end

This is covered by this test, as the munmap() matching the exact boundaries of
the VDSO is handled too.

Am I missing something ?

Well if this is the intention, then you missed to add a comment explaining it :)

Thanks,

	tglx

You're right, and I was thinking the same when I read that code this morning ;)

I'll propose a patch to a add an explicit comment.

Thanks,
Laurent.




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