+ exec-use-force_uaccess_begin-during-exec-and-exit.patch added to -mm tree

+ exec-use-force_uaccess_begin-during-exec-and-exit.patch added to -mm tree

[akpm]

The patch titled
     Subject: exec: use force_uaccess_begin during exec and exit
has been added to the -mm tree.  Its filename is
     exec-use-force_uaccess_begin-during-exec-and-exit.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/exec-use-force_uaccess_begin-during-exec-and-exit.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/exec-use-force_uaccess_begin-during-exec-and-exit.patch

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------------------------------------------------------
From: Christoph Hellwig <hch@lst.de>
Subject: exec: use force_uaccess_begin during exec and exit

Both exec and exit want to ensure that the uaccess routines actually do
access user pointers.  Use the newly added force_uaccess_begin helper
instead of an open coded set_fs for that to prepare for kernel builds
where set_fs() does not exist.

Link: http://lkml.kernel.org/r/20200710135706.537715-7-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nick Hu <nickhu@andestech.com>
Cc: Greentime Hu <green.hu@gmail.com>
Cc: Vincent Chen <deanbo422@gmail.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/exec.c     |    7 ++++++-
 kernel/exit.c |    2 +-
 2 files changed, 7 insertions(+), 2 deletions(-)

--- a/fs/exec.c~exec-use-force_uaccess_begin-during-exec-and-exit
+++ a/fs/exec.c
@@ -1380,7 +1380,12 @@ int begin_new_exec(struct linux_binprm *
 	if (retval)
 		goto out_unlock;
 
-	set_fs(USER_DS);
+	/*
+	 * Ensure that the uaccess routines can actually operate on userspace
+	 * pointers:
+	 */
+	force_uaccess_begin();
+
 	me->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
 					PF_NOFREEZE | PF_NO_SETAFFINITY);
 	flush_thread();
--- a/kernel/exit.c~exec-use-force_uaccess_begin-during-exec-and-exit
+++ a/kernel/exit.c
@@ -731,7 +731,7 @@ void __noreturn do_exit(long code)
 	 * mm_release()->clear_child_tid() from writing to a user-controlled
 	 * kernel address.
 	 */
-	set_fs(USER_DS);
+	force_uaccess_begin();
 
 	if (unlikely(in_atomic())) {
 		pr_info("note: %s[%d] exited with preempt_count %d\n",
_

Patches currently in -mm which might be from hch@lst.de are

syscalls-use-uaccess_kernel-in-addr_limit_user_check.patch
nds32-use-uaccess_kernel-in-show_regs.patch
riscv-include-asm-pgtableh-in-asm-uaccessh.patch
uaccess-remove-segment_eq.patch
uaccess-add-force_uaccess_beginend-helpers.patch
exec-use-force_uaccess_begin-during-exec-and-exit.patch