[RH7,1/2] ms/extable: Enable RCU if it is not watching in kernel_text_address()

Submitted by Vasily Averin on Nov. 20, 2020, 6:20 a.m.


Message ID 034cd568-e9e9-c876-82ff-6c1c8391f38e@virtuozzo.com
State New
Series "Series without cover letter"
Headers show

Commit Message

Vasily Averin Nov. 20, 2020, 6:20 a.m.
Author: Steven Rostedt (VMware) <rostedt@goodmis.org>
backported upstream commit e8cac8b1d10589be45671a5ade0926a639b543b7
    extable: Enable RCU if it is not watching in kernel_text_address()

    If kernel_text_address() is called when RCU is not watching, it can cause an
    RCU bug because is_module_text_address(), the is_kprobe_*insn_slot()
    and is_bpf_text_address() functions require the use of RCU.

    Only enable RCU if it is not currently watching before it calls
    is_module_text_address(). The use of rcu_nmi_enter() is used to enable RCU
    because kernel_text_address() can happen pretty much anywhere (like an NMI),
    and even from within an NMI. It is called via save_stack_trace() that can be
    called by any WARN() or tracing function, which can happen while RCU is not
    watching (for example, going to or coming from idle, or during CPU take down
    or bring up).

    Cc: stable@vger.kernel.org
    Fixes: 0be964be0 ("module: Sanitize RCU usage and locking")
    Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

backport changes:
     context fixes, RH7/vz7 kernel does not have
      is_ftrace_trampoline() and is_kprobe_*() checks

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
 kernel/extable.c | 31 ++++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

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diff --git a/kernel/extable.c b/kernel/extable.c
index 1cb213f..21136fc 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -116,13 +116,38 @@  int __kernel_text_address(unsigned long addr)
 int kernel_text_address(unsigned long addr)
+	bool no_rcu;
+	int ret = 1;
 	if (core_kernel_text(addr))
 		return 1;
+	/*
+	 * If a stack dump happens while RCU is not watching, then
+	 * RCU needs to be notified that it requires to start
+	 * watching again. This can happen either by tracing that
+	 * triggers a stack trace, or a WARN() that happens during
+	 * coming back from idle, or cpu on or offlining.
+	 *
+	 * is_module_text_address() as well as the kprobe slots
+	 * and is_bpf_text_address() require RCU to be watching.
+	 */
+	no_rcu = !rcu_is_watching();
+	/* Treat this like an NMI as it can happen anywhere */
+	if (no_rcu)
+		rcu_nmi_enter();
 	if (is_module_text_address(addr))
-		return 1;
+		goto out;
 	if (is_bpf_text_address(addr))
-		return 1;
-	return 0;
+		goto out;
+	ret = 0;
+	if (no_rcu)
+		rcu_nmi_exit();
+	return ret;