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Le 23/04/2019 à 15:34, Thomas Gleixner a écrit :

On Tue, 23 Apr 2019, Laurent Dufour wrote:

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Le 20/04/2019 à 12:31, Michael Ellerman a écrit :

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Thomas Gleixner tglx@linutronix.de writes:

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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.