kallsyms: fix percpu vars on x86-64 with relocation.
x86-64 has a problem: per-cpu variables are actually represented by
their absolute offsets within the per-cpu area, but the symbols are
not emitted as absolute. Thus kallsyms naively creates them as offsets
from _text, meaning their values change if the kernel is relocated
(especially noticeable with CONFIG_RANDOMIZE_BASE):
$ egrep ' (gdt_|_(stext|_per_cpu_))' /root/kallsyms.nokaslr
0000000000000000 D __per_cpu_start
0000000000004000 D gdt_page
0000000000014280 D __per_cpu_end
ffffffff810001c8 T _stext
ffffffff81ee53c0 D __per_cpu_offset
$ egrep ' (gdt_|_(stext|_per_cpu_))' /root/kallsyms.kaslr1
000000001f200000 D __per_cpu_start
000000001f204000 D gdt_page
000000001f214280 D __per_cpu_end
ffffffffa02001c8 T _stext
ffffffffa10e53c0 D __per_cpu_offset
Making them absolute symbols is the Right Thing, but requires fixes to
the relocs tool. So for the moment, we add a --absolute-percpu option
which makes them absolute from a kallsyms perspective:
$ egrep ' (gdt_|_(stext|_per_cpu_))' /proc/kallsyms # no KASLR
0000000000000000 A __per_cpu_start
000000000000a000 A gdt_page
0000000000013040 A __per_cpu_end
ffffffff802001c8 T _stext
ffffffff8099b180 D __per_cpu_offset
ffffffff809a3000 D __per_cpu_load
$ egrep ' (gdt_|_(stext|_per_cpu_))' /proc/kallsyms # With KASLR
0000000000000000 A __per_cpu_start
000000000000a000 A gdt_page
0000000000013040 A __per_cpu_end
ffffffff89c001c8 T _stext
ffffffff8a39d180 D __per_cpu_offset
ffffffff8a3a5000 D __per_cpu_load
Based-on-the-original-screenplay-by: Andy Honig <ahonig@google.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Kees Cook <keescook@chromium.org>
diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 3df15f5..1237dd7 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -51,9 +51,14 @@
#define text_range_text (&text_ranges[0])
#define text_range_inittext (&text_ranges[1])
+static struct addr_range percpu_range = {
+ "__per_cpu_start", "__per_cpu_end", -1ULL, 0
+};
+
static struct sym_entry *table;
static unsigned int table_size, table_cnt;
static int all_symbols = 0;
+static int absolute_percpu = 0;
static char symbol_prefix_char = '\0';
static unsigned long long kernel_start_addr = 0;
@@ -166,6 +171,9 @@
strcpy((char *)s->sym + 1, str);
s->sym[0] = stype;
+ /* Record if we've found __per_cpu_start/end. */
+ check_symbol_range(sym, s->addr, &percpu_range, 1);
+
return 0;
}
@@ -657,6 +665,15 @@
qsort(table, table_cnt, sizeof(struct sym_entry), compare_symbols);
}
+static void make_percpus_absolute(void)
+{
+ unsigned int i;
+
+ for (i = 0; i < table_cnt; i++)
+ if (symbol_in_range(&table[i], &percpu_range, 1))
+ table[i].sym[0] = 'A';
+}
+
int main(int argc, char **argv)
{
if (argc >= 2) {
@@ -664,6 +681,8 @@
for (i = 1; i < argc; i++) {
if(strcmp(argv[i], "--all-symbols") == 0)
all_symbols = 1;
+ else if (strcmp(argv[i], "--absolute-percpu") == 0)
+ absolute_percpu = 1;
else if (strncmp(argv[i], "--symbol-prefix=", 16) == 0) {
char *p = &argv[i][16];
/* skip quote */
@@ -680,6 +699,8 @@
usage();
read_map(stdin);
+ if (absolute_percpu)
+ make_percpus_absolute();
sort_symbols();
optimize_token_table();
write_src();