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Subject[RFC v2 1/7] mm: Provide generic VDSO unmap and remap functions
Date
When Address Space Layout Randomization (ASLR, randmaps) is enabled, the
address of the VDSO fluctuates from one process to the next. If
Checkpoint/Restore In Userspace (CRIU) is to fully replicate the memory map
of a previous process, it must be able to remap the VDSO of a new process
to the address used by the previous process. Historically this has been
implemented in architecture-specific code for PowerPC and x86. In order to
support 32-bit and 64-bit ARM without further duplication of code, copy
Laurent Dufour's implementation for PowerPC with slight modifications to a
generic location. This is hopefully the beginning of a long process of VDSO
code de-duplication between architectures.

Signed-off-by: Christopher Covington <cov@codeaurora.org>
---
include/asm-generic/mm_hooks.h | 35 ++++++++++++++++++++++++++++++++---
1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/include/asm-generic/mm_hooks.h b/include/asm-generic/mm_hooks.h
index cc5d9a1..73f09f1 100644
--- a/include/asm-generic/mm_hooks.h
+++ b/include/asm-generic/mm_hooks.h
@@ -1,7 +1,17 @@
/*
- * Define generic no-op hooks for arch_dup_mmap, arch_exit_mmap
- * and arch_unmap to be included in asm-FOO/mmu_context.h for any
- * arch FOO which doesn't need to hook these.
+ * Define generic hooks for arch_dup_mmap, arch_exit_mmap and arch_unmap to be
+ * included in asm-FOO/mmu_context.h for any arch FOO which doesn't need to
+ * specially hook these.
+ *
+ * arch_remap originally from include/linux-mm-arch-hooks.h
+ * arch_unmap originally from arch/powerpc/include/asm/mmu_context.h
+ * Copyright (C) 2015, IBM Corporation
+ * Author: Laurent Dufour <ldufour@linux.vnet.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
*/
#ifndef _ASM_GENERIC_MM_HOOKS_H
#define _ASM_GENERIC_MM_HOOKS_H
@@ -19,6 +29,25 @@ static inline void arch_unmap(struct mm_struct *mm,
struct vm_area_struct *vma,
unsigned long start, unsigned long end)
{
+#ifdef CONFIG_GENERIC_VDSO
+ if (start <= mm->context.vdso && mm->context.vdso < end)
+ mm->context.vdso = 0;
+#endif /* CONFIG_GENERIC_VDSO */
+}
+
+static inline void arch_remap(struct mm_struct *mm,
+ unsigned long old_start, unsigned long old_end,
+ unsigned long new_start, unsigned long new_end)
+{
+#ifdef CONFIG_GENERIC_VDSO
+ /*
+ * mremap() doesn't allow moving multiple vmas so we can limit the
+ * check to old_addr == vdso.
+ */
+ if (old_addr == mm->context.vdso)
+ mm->context.vdso = new_addr;
+
+#endif /* CONFIG_GENERIC_VDSO */
}

static inline void arch_bprm_mm_init(struct mm_struct *mm,
--
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Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.
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