> > One of Vlastimil's comments made me go dig back in to the uprobes > code's use of get_user_pages(). I decided to change both of them > to be "foreign" accesses. > > This also fixes the nommu breakage that Vlastimil noted last time. > > Srikar, I'd appreciate if you can have a look at the uprobes.c > modifications, especially the comment. I don't think this will > change any behavior, but I want to make sure the comment is > accurate. > > --- > > From: Dave Hansen <dave.han...@linux.intel.com> > > For protection keys, we need to understand whether protections > should be enforced in software or not. In general, we enforce > protections when working on our own task, but not when on others. > We call these "current" and "foreign" operations. > > This patch introduces a new get_user_pages() variant: > > get_user_pages_foreign() > > We modify the vanilla get_user_pages() so it can no longer be > used on mm/tasks other than 'current/current->mm', which is by > far the most common way it is called. Using it makes a few of > the call sites look a bit nicer. > > In other words, get_user_pages_foreign() is a replacement for > when get_user_pages() is called on non-current tsk/mm. > > This also switches get_user_pages_(un)locked() over to be like > get_user_pages() and not take a tsk/mm. There is no > get_user_pages_foreign_(un)locked(). If someone wants that > behavior they just have to use "__" variant and pass in > FOLL_FOREIGN explicitly. > > The uprobes is_trap_at_addr() location holds mmap_sem and > calls get_user_pages(current->mm) on an instruction address. This > makes it a pretty unique gup caller. Being an instruction access > and also really originating from the kernel (vs. the app), I opted > to consider this a 'foreign' access where protection keys will not > be enforced. >
Changes for uprobes.c looks good to me. Acked-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com> > Signed-off-by: Dave Hansen <dave.han...@linux.intel.com> > Cc: Andrew Morton <a...@linux-foundation.org> > Cc: Kirill A. Shutemov <kirill.shute...@linux.intel.com> > Cc: Andrea Arcangeli <aarca...@redhat.com> > Cc: Naoya Horiguchi <n-horigu...@ah.jp.nec.com> > Cc: Srikar Dronamraju <sri...@linux.vnet.ibm.com> > Cc: vba...@suse.cz > Cc: j...@suse.cz > diff -puN kernel/events/uprobes.c~get_current_user_pages > kernel/events/uprobes.c > --- a/kernel/events/uprobes.c~get_current_user_pages 2016-01-22 > 08:43:42.602473969 -0800 > +++ b/kernel/events/uprobes.c 2016-01-22 09:36:14.203845894 -0800 > @@ -299,7 +299,7 @@ int uprobe_write_opcode(struct mm_struct > > retry: > /* Read the page with vaddr into memory */ > - ret = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &old_page, &vma); > + ret = get_user_pages_foreign(NULL, mm, vaddr, 1, 0, 1, &old_page, &vma); > if (ret <= 0) > return ret; > > @@ -1700,7 +1700,13 @@ static int is_trap_at_addr(struct mm_str > if (likely(result == 0)) > goto out; > > - result = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &page, NULL); > + /* > + * The NULL 'tsk' here ensures that any faults that occur here > + * will not be accounted to the task. 'mm' *is* current->mm, > + * but we treat this as a 'foreign' access since it is > + * essentially a kernel access to the memory. > + */ > + result = get_user_pages_foreign(NULL, mm, vaddr, 1, 0, 1, &page, NULL); > if (result < 0) > return result; > -- Thanks and Regards Srikar Dronamraju
