From 85d7809e0ca80b94fd23a753e0894b8843d38367 Mon Sep 17 00:00:00 2001 From: Yidi Lin Date: Tue, 31 Oct 2023 18:50:06 +0800 Subject: arch/arm64/arch_timer: Fix possible overflow in multiplication The value from raw_read_cntfrq_el0() could be large enough to cause overflow when multiplied by USECS_PER_SEC. To prevent this, both USECS_PER_SEC and tfreq can be reduced by dividing them by their GCD. BUG=b:307790895 TEST=emerge-geralt coreboot TEST=boot to kernel and check the timestamps from `cbmem` Change-Id: I366667de05392913150414f0fa9058725be71c52 Signed-off-by: Yidi Lin Reviewed-on: https://review.coreboot.org/c/coreboot/+/78800 Reviewed-by: Yu-Ping Wu Tested-by: build bot (Jenkins) --- src/arch/arm64/arch_timer.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) (limited to 'src/arch/arm64/arch_timer.c') diff --git a/src/arch/arm64/arch_timer.c b/src/arch/arm64/arch_timer.c index 089afee385..3eb5656a15 100644 --- a/src/arch/arm64/arch_timer.c +++ b/src/arch/arm64/arch_timer.c @@ -1,12 +1,29 @@ /* SPDX-License-Identifier: GPL-2.0-only */ -#include #include +#include +#include void timer_monotonic_get(struct mono_time *mt) { uint64_t tvalue = raw_read_cntpct_el0(); - uint32_t tfreq = raw_read_cntfrq_el0(); - long usecs = (tvalue * 1000000) / tfreq; + static uint32_t tfreq, mult; + uint32_t div; + + /* + * The value from raw_read_cntfrq_el0() could be large enough to + * cause overflow when multiplied by USECS_PER_SEC. To prevent this, + * both USECS_PER_SEC. and tfreq can be reduced by dividing them by + * their GCD. + */ + if (tfreq == 0) { + tfreq = raw_read_cntfrq_el0(); + mult = USECS_PER_SEC; + div = gcd32(tfreq, mult); + tfreq /= div; + mult /= div; + } + + long usecs = (tvalue * mult) / tfreq; mono_time_set_usecs(mt, usecs); } -- cgit v1.2.3