Le 20/04/2019 à 12:31, Michael Ellerman a écrit :
Thomas Gleixner <tglx@xxxxxxxxxxxxx> writes:
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???
I don't know for sure but I think it should be fine. That code is just
there to handle CRIU unmapping/remapping the VDSO. So that either needs
to happen while the process is stopped or it needs to handle races
anyway, so I don't see how the placement within the unmap path should
matter.
My only concern is the error path.
Calling arch_unmap() before handling any error case means that it will
have to be undo and there is no way to do so.
I don't know what is the rational to move arch_unmap() to the beginning
of __do_munmap() but the error paths must be managed.
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 ?
Cheers,
Laurent.
