Messages in this thread | | | Date | Thu, 19 Jan 2017 23:20:08 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC][PATCH] x86: Verify access_ok() context |
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On Thu, Jan 19, 2017 at 04:27:18PM -0500, Frank Ch. Eigler wrote: > Hi, Thomas - > > > Well, if you are not in thread context then the check is pointless: > > __range_not_ok(addr, size, user_addr_max()) > > and: > > #define user_addr_max() (current->thread.addr_limit.seg) > > > > So what guarantees when you are not in context of current, i.e. in thread > > context, that the addr/size which is checked against the limits of current > > actually belongs to current? > > We're probably in task context in that there is a valid current(), but > running with preemption and/or interrupts and/or pagefaults disabled > at that point, so in_task() objects. Think of it like from a kprobes > handler callback, except maybe more temporary preemption blocking.
#define in_task() (!(preempt_count() & \ (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
So it doesn't care about preempt_disable(), and it doesn't care about local_irq_disable(), it also doesn't care about local_bh_disable().
What it does care about are nmi_enter(), irq_enter() and __do_softirq().
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