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kallsyms: fix percpu vars on x86-64 with relocation.

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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>
This commit is contained in:
Rusty Russell 2014-03-17 14:05:46 +10:30
parent 78eb71594b
commit c6bda7c988
2 changed files with 25 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

21
scripts/kallsyms.c
View file

@ -51,9 +51,14 @@ static struct addr_range text_ranges[] = {
#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 @@ static int read_symbol(FILE *in, struct sym_entry *s)
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 @@ static void sort_symbols(void)
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 @@ int main(int argc, char **argv)
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 @@ int main(int argc, char **argv)
usage();
read_map(stdin);
if (absolute_percpu)
make_percpus_absolute();
sort_symbols();
optimize_token_table();
write_src();

4
scripts/link-vmlinux.sh
View file

@ -86,6 +86,10 @@ kallsyms()
kallsymopt="${kallsymopt} --page-offset=$CONFIG_PAGE_OFFSET"
fi
if [ -n "${CONFIG_X86_64}" ]; then
kallsymopt="${kallsymopt} --absolute-percpu"
fi
local aflags="${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL} \
${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS}"