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[PATCH] hw/intc/sifive_clint: Fix overflow in sifive_clint_write_timecmp

From: David Hoppenbrouwers
Subject: [PATCH] hw/intc/sifive_clint: Fix overflow in sifive_clint_write_timecmp()
Date: Mon, 16 Aug 2021 19:30:35 +0200

`next` is an `uint64_t` value, but `timer_mod` takes an `int64_t`. This
resulted in high values such as `UINT64_MAX` being converted to `-1`,
which caused an immediate timer interrupt.

By limiting `next` to `INT64_MAX` no overflow will happen while the
timer will still be effectively set to "infinitely" far in the future.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/493
Signed-off-by: David Hoppenbrouwers <david@salt-inc.org>
 hw/intc/sifive_clint.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/intc/sifive_clint.c b/hw/intc/sifive_clint.c
index 0f41e5ea1c..e65e71e5ec 100644
--- a/hw/intc/sifive_clint.c
+++ b/hw/intc/sifive_clint.c
@@ -61,6 +61,8 @@ static void sifive_clint_write_timecmp(RISCVCPU *cpu, 
uint64_t value,
     /* back to ns (note args switched in muldiv64) */
     next = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
         muldiv64(diff, NANOSECONDS_PER_SECOND, timebase_freq);
+    /* ensure next does not overflow, as timer_mod takes a signed value */
+    next = MAX(next, INT64_MAX);
     timer_mod(cpu->env.timer, next);

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