Andi Kleen wrote:
Please use a full real name for posting.
OK.
John Sigler wrote:
AFAIU, even a hard real-time OS is "defenseless" against SMIs that
kick the CPU into SMM.
There are usually chipset specific bits that can be set to disable SMMs.
See the datasheet if you can get them. Unfortunately most chipset vendors
don't give out data sheets easily.
I've asked the manufacturer to send me the data sheets.
We'll see how they react.
.globl foo
foo:
push %ebx
push %esi
cpuid
rdtsc
At least some SMM implementations restore the old TSC value. Sad but true.
Why would they do that?
How would you detect periodic SMM on such a system?
Besides RDTSC can be speculated around on some CPUs which also adds errors.
I don't understand this sentence. Could you clarify?
I've attached my kernel module (hello.c)
# : >/var/log/kern.log; cat /proc/interrupts; /bin/time insmod houba.ko;
cat /proc/interrupts; rmmod houba
CPU0
0: 519083 XT-PIC-XT timer
2: 0 XT-PIC-XT cascade
9: 0 XT-PIC-XT acpi
10: 9786 XT-PIC-XT eth0
11: 5 XT-PIC-XT eth1
12: 5 XT-PIC-XT eth2
14: 16920 XT-PIC-XT ide0
NMI: 0
ERR: 0
0.00user 0.00system 5:00.00elapsed 0%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+111minor)pagefaults 0swaps
CPU0
0: 549094 XT-PIC-XT timer
2: 0 XT-PIC-XT cascade
9: 0 XT-PIC-XT acpi
10: 9791 XT-PIC-XT eth0
11: 5 XT-PIC-XT eth1
12: 5 XT-PIC-XT eth2
14: 16970 XT-PIC-XT ide0
NMI: 0
ERR: 0
(HZ=100)
30011 timer interrupts
5 eth0 interrupts
50 ide0 interrupts
# cat /var/log/kern.log
Apr 17 18:22:27 SEND kernel: INIT
Apr 17 18:27:27 SEND kernel: 2350080 29995
Apr 17 18:27:27 SEND kernel: 2369792 1
Apr 17 18:27:27 SEND kernel: 2440192 1
Apr 17 18:27:27 SEND kernel: 2441216 1
Apr 17 18:27:27 SEND kernel: 2583296 1
Apr 17 18:27:27 SEND kernel: 2852096 1
Apr 17 18:27:27 SEND kernel: EXIT
First column is the cycle count clamped to a multiple of 256.
(1266.7 MHz CPU)
Second column is occurence count.
In the second experiment, I added the IRQ disable/enable around foo.
# : >/var/log/kern.log; cat /proc/interrupts; /bin/time insmod houba.ko;
cat /proc/interrupts; rmmod houba
CPU0
0: 583666 XT-PIC-XT timer
2: 0 XT-PIC-XT cascade
9: 0 XT-PIC-XT acpi
10: 10084 XT-PIC-XT eth0
11: 5 XT-PIC-XT eth1
12: 5 XT-PIC-XT eth2
14: 17012 XT-PIC-XT ide0
NMI: 0
ERR: 0
0.00user 0.01system 5:00.00elapsed 0%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+110minor)pagefaults 0swaps
CPU0
0: 613677 XT-PIC-XT timer
2: 0 XT-PIC-XT cascade
9: 0 XT-PIC-XT acpi
10: 10089 XT-PIC-XT eth0
11: 5 XT-PIC-XT eth1
12: 5 XT-PIC-XT eth2
14: 17070 XT-PIC-XT ide0
NMI: 0
ERR: 0
30011 timer interrupts
5 eth0 interrupts
58 ide0 interrupts
# cat /var/log/kern.log
Apr 17 18:33:12 SEND kernel: INIT
Apr 17 18:38:12 SEND kernel: 2350080 30000
Apr 17 18:38:12 SEND kernel: EXIT
In this experiment, all the calls to foo had a latency between
2350080 and 2350335 cycles (1.88528 to 1.88548 ms).
I don't think I can conclude anything based on this experiment.
I'll let it run all night long.
Regards.
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/slab.h>
MODULE_LICENSE("GPL");
#define N 30000
#define MAX 20000
extern unsigned foo(void);
static int hello_init(void)
{
int i;
int *lat;
printk(KERN_ALERT "INIT\n");
lat = kmalloc(MAX * sizeof *lat, GFP_KERNEL);
if (lat == NULL) return -1;
for (i=0; i < MAX; ++i) lat[i] = 0;
for (i=0; i < 5; ++i) foo();
for (i=0; i < N; ++i)
{
unsigned count, res;
set_current_state(TASK_INTERRUPTIBLE);
schedule_timeout(1);
foo();
local_irq_disable();
count = foo();
local_irq_enable();
res = count >> 8;
if (res < MAX) ++lat[res]; else printk(KERN_ALERT "OUT OF RANGE\n");
}
for (i=0; i < MAX; ++i)
if (lat[i] != 0) printk(KERN_ALERT "%d %d\n", i<<8, lat[i]);
return 0;
}
static void hello_exit(void)
{
printk(KERN_ALERT "EXIT\n");
}
module_init(hello_init);
module_exit(hello_exit);
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