kernel-hardening - [PATCH v5 05/23] fork: Provide a function for copying init

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Message-ID: <20190426001143.4983-6-namit@vmware.com>
Date: Thu, 25 Apr 2019 17:11:25 -0700
From: Nadav Amit <namit@...are.com>
To: Peter Zijlstra <peterz@...radead.org>, Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <x86@...nel.org>, <hpa@...or.com>, Thomas
 Gleixner <tglx@...utronix.de>, Nadav Amit <nadav.amit@...il.com>, Dave Hansen
	<dave.hansen@...ux.intel.com>, <linux_dti@...oud.com>,
	<linux-integrity@...r.kernel.org>, <linux-security-module@...r.kernel.org>,
	<akpm@...ux-foundation.org>, <kernel-hardening@...ts.openwall.com>,
	<linux-mm@...ck.org>, <will.deacon@....com>, <ard.biesheuvel@...aro.org>,
	<kristen@...ux.intel.com>, <deneen.t.dock@...el.com>, Rick Edgecombe
	<rick.p.edgecombe@...el.com>, Nadav Amit <namit@...are.com>, Kees Cook
	<keescook@...omium.org>, Dave Hansen <dave.hansen@...el.com>
Subject: [PATCH v5 05/23] fork: Provide a function for copying init_mm

Provide a function for copying init_mm. This function will be later used
for setting a temporary mm.

Cc: Andy Lutomirski <luto@...nel.org>
Cc: Kees Cook <keescook@...omium.org>
Cc: Dave Hansen <dave.hansen@...el.com>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>
Tested-by: Masami Hiramatsu <mhiramat@...nel.org>
Signed-off-by: Nadav Amit <namit@...are.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
---
 include/linux/sched/task.h |  1 +
 kernel/fork.c              | 24 ++++++++++++++++++------
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h
index 2e97a2227045..f1227f2c38a4 100644
--- a/include/linux/sched/task.h
+++ b/include/linux/sched/task.h
@@ -76,6 +76,7 @@ extern void exit_itimers(struct signal_struct *);
 extern long _do_fork(unsigned long, unsigned long, unsigned long, int __user *, int __user *, unsigned long);
 extern long do_fork(unsigned long, unsigned long, unsigned long, int __user *, int __user *);
 struct task_struct *fork_idle(int);
+struct mm_struct *copy_init_mm(void);
 extern pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
 extern long kernel_wait4(pid_t, int __user *, int, struct rusage *);
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 9dcd18aa210b..099cca8f701c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1298,13 +1298,20 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm)
 		complete_vfork_done(tsk);
 }
 
-/*
- * Allocate a new mm structure and copy contents from the
- * mm structure of the passed in task structure.
+/**
+ * dup_mm() - duplicates an existing mm structure
+ * @tsk: the task_struct with which the new mm will be associated.
+ * @oldmm: the mm to duplicate.
+ *
+ * Allocates a new mm structure and duplicates the provided @oldmm structure
+ * content into it.
+ *
+ * Return: the duplicated mm or NULL on failure.
  */
-static struct mm_struct *dup_mm(struct task_struct *tsk)
+static struct mm_struct *dup_mm(struct task_struct *tsk,
+				struct mm_struct *oldmm)
 {
-	struct mm_struct *mm, *oldmm = current->mm;
+	struct mm_struct *mm;
 	int err;
 
 	mm = allocate_mm();
@@ -1371,7 +1378,7 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk)
 	}
 
 	retval = -ENOMEM;
-	mm = dup_mm(tsk);
+	mm = dup_mm(tsk, current->mm);
 	if (!mm)
 		goto fail_nomem;
 
@@ -2186,6 +2193,11 @@ struct task_struct *fork_idle(int cpu)
 	return task;
 }
 
+struct mm_struct *copy_init_mm(void)
+{
+	return dup_mm(NULL, &init_mm);
+}
+
 /*
  *  Ok, this is the main fork-routine.
  *
-- 
2.17.1
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