kallsyms: fix percpu vars on x86-64 with relocation. (c6bda7c9) · Commits · 戴 / test

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>

scripts/kallsyms.c

+21 −0

Original line number	Diff line number	Diff line
		@@ -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();

scripts/link-vmlinux.sh

+4 −0

Original line number	Diff line number	Diff line
		@@ -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}"

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