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libpayload/libc/time: Fix possible overflow in multiplication

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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 hz can be reduced by dividing them by their GCD.

This patch also modifies the return type of `timer_hz()` from
`uint64_t` to `uint32_t`, assuming that in practice the timestamp
counter should never be that fast.

BUG=b:307790895
TEST=boot to kernel and check the timestamps from `cbmem`

Change-Id: Ia55532490651fcf47128b83a8554751f050bcc89
Signed-off-by: Yidi Lin <yidilin@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78888
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
This commit is contained in:
Yidi Lin
2023-11-02 14:17:02 +08:00
committed by Julius Werner
parent e91785dfd8
commit eabdd0252a
5 changed files with 16 additions and 9 deletions
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13
payloads/libpayload/libc/time.c
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@ -38,6 +38,7 @@
#if CONFIG(LP_ARCH_X86) && CONFIG(LP_NVRAM)
#include <arch/rdtsc.h>
#endif
#include <commonlib/bsd/gcd.h>
#include <inttypes.h>
extern u32 cpu_khz;
@ -170,17 +171,21 @@ void arch_ndelay(uint64_t ns)
u64 timer_us(u64 base)
{
static u64 hz;
static u32 hz, mult = USECS_PER_SEC;
u32 div;
// Only check timer_hz once. Assume it doesn't change.
if (hz == 0) {
hz = timer_hz();
if (hz < 1000000) {
printf("Timer frequency %" PRIu64 " is too low, "
if (hz < mult) {
printf("Timer frequency %" PRIu32 " is too low, "
"must be at least 1MHz.\n", hz);
halt();
}
div = gcd32(hz, mult);
hz /= div;
mult /= div;
}
return (1000000 * timer_raw_value()) / hz - base;
return (mult * timer_raw_value()) / hz - base;
}