blob: e9ce703fa842b417a7d37133ef66c1bc5279d521 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
|
From: Frank Rowand <frank.rowand@am.sony.com>
Date: Sat, 1 Oct 2011 18:58:13 -0700
Subject: [PATCH 080/342] ARM: Initialize split page table locks for vector
page
Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=004b09285edbce245a32c7ba47b4c0d1ce080afe
Without this patch, ARM can not use SPLIT_PTLOCK_CPUS if
PREEMPT_RT_FULL=y because vectors_user_mapping() creates a
VM_ALWAYSDUMP mapping of the vector page (address 0xffff0000), but no
ptl->lock has been allocated for the page. An attempt to coredump
that page will result in a kernel NULL pointer dereference when
follow_page() attempts to lock the page.
The call tree to the NULL pointer dereference is:
do_notify_resume()
get_signal_to_deliver()
do_coredump()
elf_core_dump()
get_dump_page()
__get_user_pages()
follow_page()
pte_offset_map_lock() <----- a #define
...
rt_spin_lock()
The underlying problem is exposed by mm-shrink-the-page-frame-to-rt-size.patch.
Signed-off-by: Frank Rowand <frank.rowand@am.sony.com>
Cc: Frank <Frank_Rowand@sonyusa.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/4E87C535.2030907@am.sony.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/arm/kernel/process.c | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 82ab015bf42b..8d3c7ce34c24 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -324,6 +324,30 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
}
#ifdef CONFIG_MMU
+/*
+ * CONFIG_SPLIT_PTLOCK_CPUS results in a page->ptl lock. If the lock is not
+ * initialized by pgtable_page_ctor() then a coredump of the vector page will
+ * fail.
+ */
+static int __init vectors_user_mapping_init_page(void)
+{
+ struct page *page;
+ unsigned long addr = 0xffff0000;
+ pgd_t *pgd;
+ pud_t *pud;
+ pmd_t *pmd;
+
+ pgd = pgd_offset_k(addr);
+ pud = pud_offset(pgd, addr);
+ pmd = pmd_offset(pud, addr);
+ page = pmd_page(*(pmd));
+
+ pgtable_page_ctor(page);
+
+ return 0;
+}
+late_initcall(vectors_user_mapping_init_page);
+
#ifdef CONFIG_KUSER_HELPERS
/*
* The vectors page is always readable from user space for the
|
