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59d5af67 | 1 | From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 |
321d628a FG |
2 | From: Thomas Gleixner <tglx@linutronix.de> |
3 | Date: Thu, 14 Dec 2017 12:27:31 +0100 | |
59d5af67 | 4 | Subject: [PATCH] x86/ldt: Prevent LDT inheritance on exec |
321d628a FG |
5 | MIME-Version: 1.0 |
6 | Content-Type: text/plain; charset=UTF-8 | |
7 | Content-Transfer-Encoding: 8bit | |
8 | ||
9 | CVE-2017-5754 | |
10 | ||
11 | The LDT is inherited across fork() or exec(), but that makes no sense | |
12 | at all because exec() is supposed to start the process clean. | |
13 | ||
14 | The reason why this happens is that init_new_context_ldt() is called from | |
15 | init_new_context() which obviously needs to be called for both fork() and | |
16 | exec(). | |
17 | ||
18 | It would be surprising if anything relies on that behaviour, so it seems to | |
19 | be safe to remove that misfeature. | |
20 | ||
21 | Split the context initialization into two parts. Clear the LDT pointer and | |
22 | initialize the mutex from the general context init and move the LDT | |
23 | duplication to arch_dup_mmap() which is only called on fork(). | |
24 | ||
25 | Signed-off-by: Thomas Gleixner <tglx@linutronix.de> | |
26 | Signed-off-by: Peter Zijlstra <peterz@infradead.org> | |
27 | Cc: Andy Lutomirski <luto@kernel.org> | |
28 | Cc: Andy Lutomirsky <luto@kernel.org> | |
29 | Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> | |
30 | Cc: Borislav Petkov <bp@alien8.de> | |
31 | Cc: Borislav Petkov <bpetkov@suse.de> | |
32 | Cc: Brian Gerst <brgerst@gmail.com> | |
33 | Cc: Dave Hansen <dave.hansen@intel.com> | |
34 | Cc: Dave Hansen <dave.hansen@linux.intel.com> | |
35 | Cc: David Laight <David.Laight@aculab.com> | |
36 | Cc: Denys Vlasenko <dvlasenk@redhat.com> | |
37 | Cc: Eduardo Valentin <eduval@amazon.com> | |
38 | Cc: Greg KH <gregkh@linuxfoundation.org> | |
39 | Cc: H. Peter Anvin <hpa@zytor.com> | |
40 | Cc: Josh Poimboeuf <jpoimboe@redhat.com> | |
41 | Cc: Juergen Gross <jgross@suse.com> | |
42 | Cc: Linus Torvalds <torvalds@linux-foundation.org> | |
43 | Cc: Will Deacon <will.deacon@arm.com> | |
44 | Cc: aliguori@amazon.com | |
45 | Cc: dan.j.williams@intel.com | |
46 | Cc: hughd@google.com | |
47 | Cc: keescook@google.com | |
48 | Cc: kirill.shutemov@linux.intel.com | |
49 | Cc: linux-mm@kvack.org | |
50 | Signed-off-by: Ingo Molnar <mingo@kernel.org> | |
51 | (cherry picked from commit a4828f81037f491b2cc986595e3a969a6eeb2fb5) | |
52 | Signed-off-by: Andy Whitcroft <apw@canonical.com> | |
53 | Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com> | |
54 | (cherry picked from commit f90d254204df4b336731f23bb5417226f51e8651) | |
55 | Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com> | |
56 | --- | |
57 | arch/x86/include/asm/mmu_context.h | 21 ++++++++++++++------- | |
58 | arch/x86/kernel/ldt.c | 18 +++++------------- | |
59 | tools/testing/selftests/x86/ldt_gdt.c | 9 +++------ | |
60 | 3 files changed, 22 insertions(+), 26 deletions(-) | |
61 | ||
62 | diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h | |
63 | index dd865c2acb9d..47ec51a821e8 100644 | |
64 | --- a/arch/x86/include/asm/mmu_context.h | |
65 | +++ b/arch/x86/include/asm/mmu_context.h | |
66 | @@ -56,11 +56,17 @@ struct ldt_struct { | |
67 | /* | |
68 | * Used for LDT copy/destruction. | |
69 | */ | |
70 | -int init_new_context_ldt(struct task_struct *tsk, struct mm_struct *mm); | |
71 | +static inline void init_new_context_ldt(struct mm_struct *mm) | |
72 | +{ | |
73 | + mm->context.ldt = NULL; | |
74 | + init_rwsem(&mm->context.ldt_usr_sem); | |
75 | +} | |
76 | +int ldt_dup_context(struct mm_struct *oldmm, struct mm_struct *mm); | |
77 | void destroy_context_ldt(struct mm_struct *mm); | |
78 | #else /* CONFIG_MODIFY_LDT_SYSCALL */ | |
79 | -static inline int init_new_context_ldt(struct task_struct *tsk, | |
80 | - struct mm_struct *mm) | |
81 | +static inline void init_new_context_ldt(struct mm_struct *mm) { } | |
82 | +static inline int ldt_dup_context(struct mm_struct *oldmm, | |
83 | + struct mm_struct *mm) | |
84 | { | |
85 | return 0; | |
86 | } | |
87 | @@ -136,15 +142,16 @@ static inline int init_new_context(struct task_struct *tsk, | |
88 | mm->context.ctx_id = atomic64_inc_return(&last_mm_ctx_id); | |
89 | atomic64_set(&mm->context.tlb_gen, 0); | |
90 | ||
91 | - #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS | |
92 | +#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS | |
93 | if (cpu_feature_enabled(X86_FEATURE_OSPKE)) { | |
94 | /* pkey 0 is the default and always allocated */ | |
95 | mm->context.pkey_allocation_map = 0x1; | |
96 | /* -1 means unallocated or invalid */ | |
97 | mm->context.execute_only_pkey = -1; | |
98 | } | |
99 | - #endif | |
100 | - return init_new_context_ldt(tsk, mm); | |
101 | +#endif | |
102 | + init_new_context_ldt(mm); | |
103 | + return 0; | |
104 | } | |
105 | static inline void destroy_context(struct mm_struct *mm) | |
106 | { | |
107 | @@ -180,7 +187,7 @@ do { \ | |
108 | static inline int arch_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm) | |
109 | { | |
110 | paravirt_arch_dup_mmap(oldmm, mm); | |
111 | - return 0; | |
112 | + return ldt_dup_context(oldmm, mm); | |
113 | } | |
114 | ||
115 | static inline void arch_exit_mmap(struct mm_struct *mm) | |
116 | diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c | |
117 | index 3e7208f0c350..74a5aaf13f3c 100644 | |
118 | --- a/arch/x86/kernel/ldt.c | |
119 | +++ b/arch/x86/kernel/ldt.c | |
120 | @@ -130,28 +130,20 @@ static void free_ldt_struct(struct ldt_struct *ldt) | |
121 | } | |
122 | ||
123 | /* | |
124 | - * we do not have to muck with descriptors here, that is | |
125 | - * done in switch_mm() as needed. | |
126 | + * Called on fork from arch_dup_mmap(). Just copy the current LDT state, | |
127 | + * the new task is not running, so nothing can be installed. | |
128 | */ | |
129 | -int init_new_context_ldt(struct task_struct *tsk, struct mm_struct *mm) | |
130 | +int ldt_dup_context(struct mm_struct *old_mm, struct mm_struct *mm) | |
131 | { | |
132 | struct ldt_struct *new_ldt; | |
133 | - struct mm_struct *old_mm; | |
134 | int retval = 0; | |
135 | ||
136 | - init_rwsem(&mm->context.ldt_usr_sem); | |
137 | - | |
138 | - old_mm = current->mm; | |
139 | - if (!old_mm) { | |
140 | - mm->context.ldt = NULL; | |
141 | + if (!old_mm) | |
142 | return 0; | |
143 | - } | |
144 | ||
145 | mutex_lock(&old_mm->context.lock); | |
146 | - if (!old_mm->context.ldt) { | |
147 | - mm->context.ldt = NULL; | |
148 | + if (!old_mm->context.ldt) | |
149 | goto out_unlock; | |
150 | - } | |
151 | ||
152 | new_ldt = alloc_ldt_struct(old_mm->context.ldt->nr_entries); | |
153 | if (!new_ldt) { | |
154 | diff --git a/tools/testing/selftests/x86/ldt_gdt.c b/tools/testing/selftests/x86/ldt_gdt.c | |
155 | index 8e290c9b2c3f..783e1a754b78 100644 | |
156 | --- a/tools/testing/selftests/x86/ldt_gdt.c | |
157 | +++ b/tools/testing/selftests/x86/ldt_gdt.c | |
158 | @@ -626,13 +626,10 @@ static void do_multicpu_tests(void) | |
159 | static int finish_exec_test(void) | |
160 | { | |
161 | /* | |
162 | - * In a sensible world, this would be check_invalid_segment(0, 1); | |
163 | - * For better or for worse, though, the LDT is inherited across exec. | |
164 | - * We can probably change this safely, but for now we test it. | |
165 | + * Older kernel versions did inherit the LDT on exec() which is | |
166 | + * wrong because exec() starts from a clean state. | |
167 | */ | |
168 | - check_valid_segment(0, 1, | |
169 | - AR_DPL3 | AR_TYPE_XRCODE | AR_S | AR_P | AR_DB, | |
170 | - 42, true); | |
171 | + check_invalid_segment(0, 1); | |
172 | ||
173 | return nerrs ? 1 : 0; | |
174 | } | |
175 | -- | |
176 | 2.14.2 | |
177 |