linux-kernel - [RFC PATCH] mm, oom_reaper: gather each vma to prevent leaking TLB entry

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 6 Nov 2017 03:36:51 +0000
From:   Wang Nan <wangnan0@...wei.com>
To:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
CC:     Wang Nan <wangnan0@...wei.com>, Bob Liu <liubo95@...wei.com>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Ingo Molnar <mingo@...nel.org>, Roman Gushchin <guro@...com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        "Andrea Arcangeli" <aarcange@...hat.com>
Subject: [RFC PATCH] mm, oom_reaper: gather each vma to prevent leaking TLB entry

tlb_gather_mmu(&tlb, mm, 0, -1) means gathering all virtual memory space.
In this case, tlb->fullmm is true. Some archs like arm64 doesn't flush
TLB when tlb->fullmm is true:

  commit 5a7862e83000 ("arm64: tlbflush: avoid flushing when fullmm == 1").

Which makes leaking of tlb entries. For example, when oom_reaper
selects a task and reaps its virtual memory space, another thread
in this task group may still running on another core and access
these already freed memory through tlb entries.

This patch gather each vma instead of gathering full vm space,
tlb->fullmm is not true. The behavior of oom reaper become similar
to munmapping before do_exit, which should be safe for all archs.

Signed-off-by: Wang Nan <wangnan0@...wei.com>
Cc: Bob Liu <liubo95@...wei.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Michal Hocko <mhocko@...e.com>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Roman Gushchin <guro@...com>
Cc: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc: Andrea Arcangeli <aarcange@...hat.com>
---
 mm/oom_kill.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index dee0f75..18c5b35 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -532,7 +532,6 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
 	 */
 	set_bit(MMF_UNSTABLE, &mm->flags);
 
-	tlb_gather_mmu(&tlb, mm, 0, -1);
 	for (vma = mm->mmap ; vma; vma = vma->vm_next) {
 		if (!can_madv_dontneed_vma(vma))
 			continue;
@@ -547,11 +546,13 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
 		 * we do not want to block exit_mmap by keeping mm ref
 		 * count elevated without a good reason.
 		 */
-		if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED))
+		if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
+			tlb_gather_mmu(&tlb, mm, vma->vm_start, vma->vm_end);
 			unmap_page_range(&tlb, vma, vma->vm_start, vma->vm_end,
 					 NULL);
+			tlb_finish_mmu(&tlb, vma->vm_start, vma->vm_end);
+		}
 	}
-	tlb_finish_mmu(&tlb, 0, -1);
 	pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
 			task_pid_nr(tsk), tsk->comm,
 			K(get_mm_counter(mm, MM_ANONPAGES)),
-- 
2.10.1