diff options
| author | Yidi Lin <yidilin@chromium.org> | 2023-10-31 18:50:06 +0800 |
|---|---|---|
| committer | Martin L Roth <gaumless@gmail.com> | 2023-11-04 17:09:00 +0000 |
| commit | 85d7809e0ca80b94fd23a753e0894b8843d38367 (patch) | |
| tree | d3feaea2d547a513f8134e599145e36ce306f852 /src | |
| parent | da1a0e891be5f6aed7af703b117a2fe60049f3bc (diff) | |
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 <yidilin@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78800
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Diffstat (limited to 'src')
| -rw-r--r-- | src/arch/arm64/arch_timer.c | 23 |
1 files changed, 20 insertions, 3 deletions
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 <timer.h> #include <arch/lib_helpers.h> +#include <commonlib/bsd/gcd.h> +#include <timer.h> 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); } |