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102 lines
3.9 KiB
Diff
102 lines
3.9 KiB
Diff
From c33d1bdff9c4c24e73e7c7f48ce8f8c1819a233f Mon Sep 17 00:00:00 2001
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From: Linus Torvalds <torvalds@linux-foundation.org>
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Date: Thu, 20 Oct 2016 14:11:10 -0700
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Subject: [PATCH] UPSTREAM: mm: remove gup_flags FOLL_WRITE games from
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__get_user_pages()
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(cherry-picked from 9691eac5593ff1e2f82391ad327f21d90322aec1)
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commit 19be0eaffa3ac7d8eb6784ad9bdbc7d67ed8e619 upstream.
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This is an ancient bug that was actually attempted to be fixed once
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(badly) by me eleven years ago in commit 4ceb5db9757a ("Fix
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get_user_pages() race for write access") but that was then undone due to
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problems on s390 by commit f33ea7f404e5 ("fix get_user_pages bug").
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In the meantime, the s390 situation has long been fixed, and we can now
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fix it by checking the pte_dirty() bit properly (and do it better). The
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s390 dirty bit was implemented in abf09bed3cce ("s390/mm: implement
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software dirty bits") which made it into v3.9. Earlier kernels will
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have to look at the page state itself.
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Also, the VM has become more scalable, and what used a purely
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theoretical race back then has become easier to trigger.
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To fix it, we introduce a new internal FOLL_COW flag to mark the "yes,
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we already did a COW" rather than play racy games with FOLL_WRITE that
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is very fundamental, and then use the pte dirty flag to validate that
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the FOLL_COW flag is still valid.
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Reported-and-tested-by: Phil "not Paul" Oester <kernel@linuxace.com>
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Acked-by: Hugh Dickins <hughd@google.com>
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Reviewed-by: Michal Hocko <mhocko@suse.com>
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Cc: Andy Lutomirski <luto@kernel.org>
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Cc: Kees Cook <keescook@chromium.org>
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Cc: Oleg Nesterov <oleg@redhat.com>
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Cc: Willy Tarreau <w@1wt.eu>
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Cc: Nick Piggin <npiggin@gmail.com>
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Cc: Greg Thelen <gthelen@google.com>
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Cc: stable@vger.kernel.org
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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[wt: s/gup.c/memory.c; s/follow_page_pte/follow_page_mask;
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s/faultin_page/__get_user_page]
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Signed-off-by: Willy Tarreau <w@1wt.eu>
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Change-Id: I42e448ecacad4781b460c4c989026307169ba1b5
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Bug: 32141528
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---
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include/linux/mm.h | 1 +
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mm/memory.c | 14 ++++++++++++--
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2 files changed, 13 insertions(+), 2 deletions(-)
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diff --git a/include/linux/mm.h b/include/linux/mm.h
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index b582c9d07fcd5..54567b0c41d63 100644
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--- a/include/linux/mm.h
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+++ b/include/linux/mm.h
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@@ -1752,6 +1752,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma,
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#define FOLL_HWPOISON 0x100 /* check page is hwpoisoned */
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#define FOLL_NUMA 0x200 /* force NUMA hinting page fault */
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#define FOLL_MIGRATION 0x400 /* wait for page to replace migration entry */
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+#define FOLL_COW 0x4000 /* internal GUP flag */
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typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
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void *data);
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diff --git a/mm/memory.c b/mm/memory.c
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index ac61bc57e3ef4..fd453654d3008 100644
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--- a/mm/memory.c
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+++ b/mm/memory.c
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@@ -1467,6 +1467,16 @@ int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
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}
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EXPORT_SYMBOL_GPL(zap_vma_ptes);
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+/*
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+ * FOLL_FORCE can write to even unwritable pte's, but only
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+ * after we've gone through a COW cycle and they are dirty.
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+ */
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+static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
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+{
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+ return pte_write(pte) ||
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+ ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
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+}
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+
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/**
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* follow_page_mask - look up a page descriptor from a user-virtual address
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* @vma: vm_area_struct mapping @address
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@@ -1574,7 +1584,7 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
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}
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if ((flags & FOLL_NUMA) && pte_numa(pte))
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goto no_page;
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- if ((flags & FOLL_WRITE) && !pte_write(pte))
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+ if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags))
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goto unlock;
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page = vm_normal_page(vma, address, pte);
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@@ -1894,7 +1904,7 @@ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
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*/
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if ((ret & VM_FAULT_WRITE) &&
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!(vma->vm_flags & VM_WRITE))
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- foll_flags &= ~FOLL_WRITE;
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+ foll_flags |= FOLL_COW;
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cond_resched();
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}
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