mm/gup: Introduce get_user_pages_remote()

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 "remote" operations.

This patch introduces a new get_user_pages() variant:

        get_user_pages_remote()

Which is a replacement for when get_user_pages() is called on
non-current tsk/mm.

We also introduce a new gup flag: FOLL_REMOTE which can be used
for the "__" gup variants to get this new behavior.

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 'remote' access where protection keys will not
be enforced.

Without protection keys, this patch should not change any behavior.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: jack@suse.cz
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20160212210154.3F0E51EA@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 8 insertions, 2 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 0167679182c0..8eef5f55d3f0 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -299,7 +299,7 @@ int uprobe_write_opcode(struct mm_struct *mm, unsigned long vaddr,
 
 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_remote(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_struct *mm, unsigned long vaddr)
 	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 'remote' access since it is
+	 * essentially a kernel access to the memory.
+	 */
+	result = get_user_pages_remote(NULL, mm, vaddr, 1, 0, 1, &page, NULL);
 	if (result < 0)
 		return result;