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
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
|
#include <xen/init.h>
#include <xen/list.h>
#include <xen/perfc.h>
#include <xen/rcupdate.h>
#include <xen/sort.h>
#include <xen/spinlock.h>
#include <asm/uaccess.h>
#include <xen/domain_page.h>
#include <xen/virtual_region.h>
#include <xen/livepatch.h>
#include <xen/warning.h>
#define EX_FIELD(ptr, field) ((unsigned long)&(ptr)->field + (ptr)->field)
static inline unsigned long ex_addr(const struct exception_table_entry *x)
{
return EX_FIELD(x, addr);
}
static inline unsigned long ex_cont(const struct exception_table_entry *x)
{
return EX_FIELD(x, cont);
}
static int init_or_livepatch cf_check cmp_ex(const void *a, const void *b)
{
const struct exception_table_entry *l = a, *r = b;
unsigned long lip = ex_addr(l);
unsigned long rip = ex_addr(r);
/* avoid overflow */
if (lip > rip)
return 1;
if (lip < rip)
return -1;
return 0;
}
static void init_or_livepatch cf_check swap_ex(void *a, void *b, size_t size)
{
struct exception_table_entry *l = a, *r = b, tmp;
long delta = b - a;
tmp = *l;
l->addr = r->addr + delta;
l->cont = r->cont + delta;
r->addr = tmp.addr - delta;
r->cont = tmp.cont - delta;
}
void init_or_livepatch sort_exception_table(struct exception_table_entry *start,
const struct exception_table_entry *stop)
{
sort(start, stop - start,
sizeof(struct exception_table_entry), cmp_ex, swap_ex);
}
void __init sort_exception_tables(void)
{
sort_exception_table(__start___ex_table, __stop___ex_table);
sort_exception_table(__start___pre_ex_table, __stop___pre_ex_table);
}
static unsigned long
search_one_extable(const struct exception_table_entry *first,
const struct exception_table_entry *end,
unsigned long value)
{
const struct exception_table_entry *last = end - 1;
const struct exception_table_entry *mid;
long diff;
while ( first <= last )
{
mid = (last - first) / 2 + first;
diff = ex_addr(mid) - value;
if (diff == 0)
return ex_cont(mid);
else if (diff < 0)
first = mid+1;
else
last = mid-1;
}
return 0;
}
unsigned long
search_exception_table(const struct cpu_user_regs *regs)
{
const struct virtual_region *region = find_text_region(regs->rip);
unsigned long stub = this_cpu(stubs.addr);
if ( region && region->ex )
return search_one_extable(region->ex, region->ex_end, regs->rip);
if ( regs->rip >= stub + STUB_BUF_SIZE / 2 &&
regs->rip < stub + STUB_BUF_SIZE &&
regs->rsp > (unsigned long)regs &&
regs->rsp < (unsigned long)get_cpu_info() )
{
unsigned long retptr = *(unsigned long *)regs->rsp;
region = find_text_region(retptr);
retptr = region && region->ex
? search_one_extable(region->ex, region->ex_end, retptr)
: 0;
if ( retptr )
{
/*
* Put trap number and error code on the stack (in place of the
* original return address) for recovery code to pick up.
*/
union stub_exception_token token = {
.fields.ec = regs->error_code,
.fields.trapnr = regs->entry_vector,
};
*(unsigned long *)regs->rsp = token.raw;
return retptr;
}
}
return 0;
}
#ifndef NDEBUG
#include <asm/traps.h>
static int __init cf_check stub_selftest(void)
{
static const struct {
uint8_t opc[8];
uint64_t rax;
union stub_exception_token res;
} tests[] __initconst = {
#define endbr64 0xf3, 0x0f, 0x1e, 0xfa
{ .opc = { endbr64, 0x0f, 0xb9, 0xc3, 0xc3 }, /* ud1 */
.res.fields.trapnr = X86_EXC_UD },
{ .opc = { endbr64, 0x90, 0x02, 0x00, 0xc3 }, /* nop; add (%rax),%al */
.rax = 0x0123456789abcdef,
.res.fields.trapnr = X86_EXC_GP },
{ .opc = { endbr64, 0x02, 0x04, 0x04, 0xc3 }, /* add (%rsp,%rax),%al */
.rax = 0xfedcba9876543210,
.res.fields.trapnr = X86_EXC_SS },
{ .opc = { endbr64, 0xcc, 0xc3, 0xc3, 0xc3 }, /* int3 */
.res.fields.trapnr = X86_EXC_BP },
#undef endbr64
};
unsigned long addr = this_cpu(stubs.addr) + STUB_BUF_SIZE / 2;
unsigned int i;
bool fail = false;
printk("Running stub recovery selftests...\n");
for ( i = 0; i < ARRAY_SIZE(tests); ++i )
{
uint8_t *ptr = map_domain_page(_mfn(this_cpu(stubs.mfn))) +
(addr & ~PAGE_MASK);
union stub_exception_token res = { .raw = ~0 };
memset(ptr, 0xcc, STUB_BUF_SIZE / 2);
memcpy(ptr, tests[i].opc, ARRAY_SIZE(tests[i].opc));
unmap_domain_page(ptr);
asm volatile ( "INDIRECT_CALL %[stb]\n"
".Lret%=:\n\t"
".pushsection .fixup,\"ax\"\n"
".Lfix%=:\n\t"
"pop %[exn]\n\t"
"jmp .Lret%=\n\t"
".popsection\n\t"
_ASM_EXTABLE(.Lret%=, .Lfix%=)
: [exn] "+m" (res) ASM_CALL_CONSTRAINT
: [stb] "r" (addr), "a" (tests[i].rax));
if ( res.raw != tests[i].res.raw )
{
printk("Selftest %u failed: Opc %*ph "
"expected %s[%04x], got %s[%04x]\n",
i, (int)ARRAY_SIZE(tests[i].opc), tests[i].opc,
vector_name(tests[i].res.fields.trapnr), tests[i].res.fields.ec,
vector_name(res.fields.trapnr), res.fields.ec);
fail = true;
}
}
if ( fail )
warning_add("SELFTEST FAILURE: CORRECT BEHAVIOR CANNOT BE GUARANTEED\n");
return 0;
}
__initcall(stub_selftest);
#endif
unsigned long
search_pre_exception_table(struct cpu_user_regs *regs)
{
unsigned long addr = regs->rip;
unsigned long fixup = search_one_extable(
__start___pre_ex_table, __stop___pre_ex_table, addr);
if ( fixup )
{
dprintk(XENLOG_INFO, "Pre-exception: %p -> %p\n", _p(addr), _p(fixup));
perfc_incr(exception_fixed);
}
return fixup;
}
|
