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SubjectRe: [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:
>
>> On Tue, Mar 27, 2018 at 12:05:23PM -0400, Mathieu Desnoyers wrote:
>> [...]
>>> Changes since v11:
>>>
>>> - Replace task struct rseq_preempt, rseq_signal, and rseq_migrate
>>> bool by u32 rseq_event_mask.
>> [...]
>>> @@ -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

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