Le 20/04/2019 à 12:31, Michael Ellerman a écrit :
Thomas Gleixner tglx@linutronix.de 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.