⬢ DragonFlyBSD Kernel Audit
DF-2675 / ptecheck.c
← back to finding ↓ download raw 
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
/*
 * DF-2675 ptecheck: dump all present 4K PTEs in the kernel half of the
 * page tables of the RUNNING system, via /dev/mem + KPML4phys (kvm_nlist).
 *
 * Usage: ptecheck > snapshot.txt
 * Each line: "<KVA> <PhysAddr>"
 *
 * Diffing two snapshots around a single getblk() shows the pages the
 * buffer installed.  A legitimate buffer can only add <= MAXBSIZE/PAGE_SIZE
 * (16) consecutive pages inside its own slot; a 17-page consecutive run is
 * the vfs_bio.c allocbuf() KVA-slot overflow signature.
 */
#include <sys/types.h>
#include <err.h>
#include <fcntl.h>
#include <kvm.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#define PMASK 0x000FFFFFFFFFF000ULL

static int memfd;
static uint64_t KPML4;

static uint64_t
rdphys(uint64_t pa, void *buf, size_t len)
{
	return (pread(memfd, buf, len, (off_t)pa) == (ssize_t)len);
}

static void
scan_pt(uint64_t ptphys, uint64_t va_base)
{
	uint64_t pt[512];
	int i;

	if (!rdphys(ptphys, pt, sizeof(pt)))
		return;
	for (i = 0; i < 512; ++i) {
		if ((pt[i] & 1) == 0)
			continue;
		if (pt[i] & 0x80)	/* 2MB page - not buffer KVA */
			continue;
		printf("%llu %llu\n",
		       (unsigned long long)(va_base + ((uint64_t)i << 12)),
		       (unsigned long long)(pt[i] & PMASK));
	}
}

int
main(int argc, char **argv)
{
	kvm_t *kd;
	struct nlist nl[] = { { "_KPML4phys" }, { NULL } };
	uint64_t pml4[512], pud[512];
	int p4, p3;

	if (argc > 1) {
		fprintf(stderr, "usage: ptecheck > file\n");
		return 1;
	}
	kd = kvm_open(NULL, NULL, NULL, O_RDONLY, "ptecheck");
	if (kd == NULL)
		return 1;
	if (kvm_nlist(kd, nl) != 0 || nl[0].n_value == 0)
		errx(1, "kvm_nlist: KPML4phys not found");
	if (kvm_read(kd, nl[0].n_value, &KPML4, sizeof(KPML4)) != sizeof(KPML4))
		errx(1, "kvm_read KPML4phys failed");
	kvm_close(kd);

	memfd = open("/dev/mem", O_RDONLY);
	if (memfd < 0)
		err(1, "open /dev/mem");
	if (!rdphys(KPML4, pml4, sizeof(pml4)))
		errx(1, "cannot read PML4 at phys %#jx", (uintmax_t)KPML4);

	for (p4 = 256; p4 < 512; ++p4) {	/* kernel half */
		if ((pml4[p4] & 1) == 0)
			continue;
		if (!rdphys(pml4[p4] & PMASK, pud, sizeof(pud)))
			continue;
		for (p3 = 0; p3 < 512; ++p3) {
			uint64_t va = ((uint64_t)p4 << 39) | ((uint64_t)p3 << 30);
			if ((pud[p3] & 1) == 0)
				continue;
			if (pud[p3] & 0x80)	/* 1GB page */
				continue;
			scan_pt(pud[p3] & PMASK, va);
		}
	}
	close(memfd);
	return 0;
}