From c6bda7c988a57958108741cde9b1f12e9727a938 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Mon, 17 Mar 2014 14:05:46 +1030 Subject: [PATCH] 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 Signed-off-by: Rusty Russell Acked-by: Kees Cook --- scripts/kallsyms.c | 21 +++++++++++++++++++++ scripts/link-vmlinux.sh | 4 ++++ 2 files changed, 25 insertions(+) diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c index 3df15f5e7c55..1237dd7fb4ca 100644 --- a/scripts/kallsyms.c +++ b/scripts/kallsyms.c @@ -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(); diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh index 2dcb37736d84..86a4fe75f453 100644 --- a/scripts/link-vmlinux.sh +++ b/scripts/link-vmlinux.sh @@ -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}" -- 2.30.2