blob: 511698c4296ed72903994951b739eff4f382b044 (
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
73
74
75
76
77
78
79
80
81
82
83
|
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Fri, 18 Oct 2019 13:04:15 +0200
Subject: [PATCH 309/342] Revert "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=954608a19dde6afa6ee3fcbc50ad717c888a9050
[ Upstream commit 247074c44d8c3e619dfde6404a52295d8d671d38 ]
I'm dropping this patch, with its original description:
|ARM: Initialize split page table locks for vector page
|
|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.
The patch named mm-shrink-the-page-frame-to-rt-size.patch was dropped
from the RT queue once the SPLIT_PTLOCK_CPUS feature (in a slightly
different shape) went upstream (somewhere between v3.12 and v3.14).
I can see that the patch still allocates a lock which wasn't there
before. However I can't trigger a kernel oops like described in the
patch by triggering a coredump.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
arch/arm/kernel/process.c | 24 ------------------------
1 file changed, 24 deletions(-)
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 8d3c7ce34c24..82ab015bf42b 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -324,30 +324,6 @@ 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
|
