Re: [RFC PATCH for 4.17 02/21] rseq: Introduce restartable sequences system call (v12)

----- On Mar 28, 2018, at 10:06 AM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:

----- On Mar 28, 2018, at 2:47 AM, Boqun Feng boqun.feng@gmail.com wrote:

quoted

On Tue, Mar 27, 2018 at 12:05:23PM -0400, Mathieu Desnoyers wrote:
[...]

quoted

Changes since v11:

- Replace task struct rseq_preempt, rseq_signal, and rseq_migrate
  bool by u32 rseq_event_mask.

[...]

quoted

@@ -979,6 +980,17 @@ struct task_struct {
 	unsigned long			numa_pages_migrated;
 #endif /* CONFIG_NUMA_BALANCING */
 
+#ifdef CONFIG_RSEQ
+	struct rseq __user *rseq;
+	u32 rseq_len;
+	u32 rseq_sig;
+	/*
+	 * RmW on rseq_event_mask must be performed atomically
+	 * with respect to preemption.
+	 */
+	unsigned long rseq_event_mask;

s/unsigned long/u32

good point, fixed.

Actually, by having a u32 instead of unsigned long here, it triggers those
warnings:

In file included from ./include/linux/bitops.h:38:0,
                 from ./include/linux/kernel.h:11,
                 from certs/system_keyring.c:13:
./arch/x86/include/asm/bitops.h:73:1: note: expected ‘volatile long unsigned int *’ but argument is of type ‘u32 *’
 set_bit(long nr, volatile unsigned long *addr)
 ^

I suspect that casting the u32 * to a unsigned long * is not a safe approach, because
the code can generate a load/store on unallocated memory (kasan might complain).

Thoughts ?

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com