Messages in this thread | | | Subject | Re: [RFC]: Possible race condition in kernel futex code | From | Hans Zuidam <> | Date | Fri, 9 Oct 2015 11:49:45 +0200 |
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Hi Thomas,
On 9 okt. 2015, at 11:06, Thomas Gleixner <tglx@linutronix.de> wrote: On Mon, 5 Oct 2015, Jaccon Bastiaansen wrote: >> We did some tests with different compilers, kernel versions and kernel >> configs, with the following results:
> You cannot use an explicit 32bit read. We need an access which handles the fault gracefully.
The reason for the explicit read suggestion is to avoid the _builtin_constant_p() in __copy_from_user_nocheck(). The GCC manual says that there may be situations where it returns 0 even though the argument is a constant. Although none of the compiler/kernel combinations we have tried showed this happening, we think it is probably better to be safe than sorry.
With kind regards, Hans Zuidam
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