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libpayload/libc/time: 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 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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
payloads/libpayload/drivers/timer/arm64_arch_timer.c
View File

@ -32,7 +32,7 @@
#include <arch/lib_helpers.h> #include <arch/lib_helpers.h>
#include <libpayload.h> #include <libpayload.h>
uint64_t timer_hz(void) uint32_t timer_hz(void)
{ {
return raw_read_cntfrq_el0(); return raw_read_cntfrq_el0();
} }

2
payloads/libpayload/drivers/timer/generic.c
View File

@ -33,7 +33,7 @@
#include <assert.h> #include <assert.h>
#include <libpayload.h> #include <libpayload.h>
uint64_t timer_hz(void) uint32_t timer_hz(void)
{ {
/* libc/time.c currently requires all timers to be at least 1MHz. */ /* libc/time.c currently requires all timers to be at least 1MHz. */
assert(CONFIG_LP_TIMER_GENERIC_HZ >= 1000000); assert(CONFIG_LP_TIMER_GENERIC_HZ >= 1000000);

6
payloads/libpayload/drivers/timer/rdtsc.c
View File

@ -33,10 +33,12 @@
#include <libpayload.h> #include <libpayload.h>
#include <arch/rdtsc.h> #include <arch/rdtsc.h>
#include <assert.h>
uint64_t timer_hz(void) uint32_t timer_hz(void)
{ {
return (uint64_t)lib_sysinfo.cpu_khz * 1000; assert(UINT32_MAX / 1000 >= lib_sysinfo.cpu_khz);
return lib_sysinfo.cpu_khz * 1000;
} }
uint64_t timer_raw_value(void) uint64_t timer_raw_value(void)

2
payloads/libpayload/include/libpayload.h
View File

@ -519,7 +519,7 @@ void lib_sysinfo_get_memranges(struct memrange **ranges,
/* Timer functions. */ /* Timer functions. */
/* Defined by each architecture. */ /* Defined by each architecture. */
uint64_t timer_hz(void); uint32_t timer_hz(void);
uint64_t timer_raw_value(void); uint64_t timer_raw_value(void);
uint64_t timer_us(uint64_t base); uint64_t timer_us(uint64_t base);
/* Generic. */ /* Generic. */

13
payloads/libpayload/libc/time.c
View File

@ -38,6 +38,7 @@
#if CONFIG(LP_ARCH_X86) && CONFIG(LP_NVRAM) #if CONFIG(LP_ARCH_X86) && CONFIG(LP_NVRAM)
#include <arch/rdtsc.h> #include <arch/rdtsc.h>
#endif #endif
#include <commonlib/bsd/gcd.h>
#include <inttypes.h> #include <inttypes.h>
extern u32 cpu_khz; extern u32 cpu_khz;
@ -170,17 +171,21 @@ void arch_ndelay(uint64_t ns)
u64 timer_us(u64 base) 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. // Only check timer_hz once. Assume it doesn't change.
if (hz == 0) { if (hz == 0) {
hz = timer_hz(); hz = timer_hz();
if (hz < 1000000) { if (hz < mult) {
printf("Timer frequency %" PRIu64 " is too low, " printf("Timer frequency %" PRIu32 " is too low, "
"must be at least 1MHz.\n", hz); "must be at least 1MHz.\n", hz);
halt(); halt();
} }
div = gcd32(hz, mult);
hz /= div;
mult /= div;
} }
return (1000000 * timer_raw_value()) / hz - base; return (mult * timer_raw_value()) / hz - base;
} }