From 4dc06bb8167fb18b8eb7e40762a94dcc36101047 Mon Sep 17 00:00:00 2001 From: David Hoppenbrouwers Date: Fri, 27 Aug 2021 17:23:25 +0200 Subject: [PATCH] hw/intc/sifive_clint: Fix muldiv64 overflow in sifive_clint_write_timecmp() `muldiv64` would overflow in cases where the final 96-bit value does not fit in a `uint64_t`. This would result in small values that cause an interrupt to be triggered much sooner than intended. The overflow can be detected in most cases by checking if the new value is smaller than the previous value. If the final result is larger than `diff` it is either correct or it doesn't matter as it is effectively infinite anyways. `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 Reviewed-by: Alistair Francis Message-id: 20210827152324.5201-1-david@salt-inc.org Signed-off-by: Alistair Francis --- hw/intc/sifive_clint.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/hw/intc/sifive_clint.c b/hw/intc/sifive_clint.c index 0f41e5ea1c..99c870ced2 100644 --- a/hw/intc/sifive_clint.c +++ b/hw/intc/sifive_clint.c @@ -59,8 +59,29 @@ static void sifive_clint_write_timecmp(RISCVCPU *cpu, uint64_t value, riscv_cpu_update_mip(cpu, MIP_MTIP, BOOL_TO_MASK(0)); diff = cpu->env.timecmp - rtc_r; /* back to ns (note args switched in muldiv64) */ - next = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + - muldiv64(diff, NANOSECONDS_PER_SECOND, timebase_freq); + uint64_t ns_diff = muldiv64(diff, NANOSECONDS_PER_SECOND, timebase_freq); + + /* + * check if ns_diff overflowed and check if the addition would potentially + * overflow + */ + if ((NANOSECONDS_PER_SECOND > timebase_freq && ns_diff < diff) || + ns_diff > INT64_MAX) { + next = INT64_MAX; + } else { + /* + * as it is very unlikely qemu_clock_get_ns will return a value + * greater than INT64_MAX, no additional check is needed for an + * unsigned integer overflow. + */ + next = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + ns_diff; + /* + * if ns_diff is INT64_MAX next may still be outside the range + * of a signed integer. + */ + next = MIN(next, INT64_MAX); + } + timer_mod(cpu->env.timer, next); }