From ffc661c99f621152d5fdcf53f9df0d48c326318b Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Mon, 30 Oct 2017 22:35:47 +0100 Subject: [PATCH] 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: Rasmus Villemoes Signed-off-by: Thomas Gleixner Link: https://lkml.kernel.org/r/20171030213548.16831-1-linux@rasmusvillemoes.dk --- kernel/irq/manage.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c index c65f282cbc9a..6a1bf9dc7a6a 100644 --- a/kernel/irq/manage.c +++ b/kernel/irq/manage.c @@ -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)) {