提交 ffc661c9 编写于 作者: R Rasmus Villemoes 提交者: Thomas Gleixner

genirq: Fix type of shifting literal 1 in __setup_irq()

If ffz() ever returns a value >= 31 then the following shift is undefined
behaviour because the literal 1 which gets shifted is treated as signed
integer.

In practice, the bug is probably harmless, since the first undefined shift
count is 31 which results - ignoring UB - in (int)(0x80000000). This gets
sign extended so bit 32-63 will be set as well and all subsequent
__setup_irq() calls would just end up hitting the -EBUSY branch.

However, a sufficiently aggressive optimizer may use the UB of 1<<31
to decide that doesn't happen, and hence elide the sign-extension
code, so that subsequent calls can indeed get ffz > 31.

In any case, the right thing to do is to make the literal 1UL.

[ tglx: For this to happen a single interrupt would have to be shared by 32
  	devices. Hardware like that does not exist and would have way more
  	problems than that. ]
Signed-off-by: NRasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20171030213548.16831-1-linux@rasmusvillemoes.dk
上级 306eb5a3
......@@ -1289,7 +1289,7 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
* thread_mask assigned. See the loop above which or's
* all existing action->thread_mask bits.
*/
new->thread_mask = 1 << ffz(thread_mask);
new->thread_mask = 1UL << ffz(thread_mask);
} else if (new->handler == irq_default_primary_handler &&
!(desc->irq_data.chip->flags & IRQCHIP_ONESHOT_SAFE)) {
......
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