forked from luck/tmp_suning_uos_patched
0b053c9518
OPTIMIZER_HIDE_VAR(), as defined when using gcc, is insufficient to
ensure protection from dead store optimization.
For the random driver and crypto drivers, calls are emitted ...
$ gdb vmlinux
(gdb) disassemble memzero_explicit
Dump of assembler code for function memzero_explicit:
0xffffffff813a18b0 <+0>: push %rbp
0xffffffff813a18b1 <+1>: mov %rsi,%rdx
0xffffffff813a18b4 <+4>: xor %esi,%esi
0xffffffff813a18b6 <+6>: mov %rsp,%rbp
0xffffffff813a18b9 <+9>: callq 0xffffffff813a7120 <memset>
0xffffffff813a18be <+14>: pop %rbp
0xffffffff813a18bf <+15>: retq
End of assembler dump.
(gdb) disassemble extract_entropy
[...]
0xffffffff814a5009 <+313>: mov %r12,%rdi
0xffffffff814a500c <+316>: mov $0xa,%esi
0xffffffff814a5011 <+321>: callq 0xffffffff813a18b0 <memzero_explicit>
0xffffffff814a5016 <+326>: mov -0x48(%rbp),%rax
[...]
... but in case in future we might use facilities such as LTO, then
OPTIMIZER_HIDE_VAR() is not sufficient to protect gcc from a possible
eviction of the memset(). We have to use a compiler barrier instead.
Minimal test example when we assume memzero_explicit() would *not* be
a call, but would have been *inlined* instead:
static inline void memzero_explicit(void *s, size_t count)
{
memset(s, 0, count);
<foo>
}
int main(void)
{
char buff[20];
snprintf(buff, sizeof(buff) - 1, "test");
printf("%s", buff);
memzero_explicit(buff, sizeof(buff));
return 0;
}
With <foo> := OPTIMIZER_HIDE_VAR():
(gdb) disassemble main
Dump of assembler code for function main:
[...]
0x0000000000400464 <+36>: callq 0x400410 <printf@plt>
0x0000000000400469 <+41>: xor %eax,%eax
0x000000000040046b <+43>: add $0x28,%rsp
0x000000000040046f <+47>: retq
End of assembler dump.
With <foo> := barrier():
(gdb) disassemble main
Dump of assembler code for function main:
[...]
0x0000000000400464 <+36>: callq 0x400410 <printf@plt>
0x0000000000400469 <+41>: movq $0x0,(%rsp)
0x0000000000400471 <+49>: movq $0x0,0x8(%rsp)
0x000000000040047a <+58>: movl $0x0,0x10(%rsp)
0x0000000000400482 <+66>: xor %eax,%eax
0x0000000000400484 <+68>: add $0x28,%rsp
0x0000000000400488 <+72>: retq
End of assembler dump.
As can be seen, movq, movq, movl are being emitted inlined
via memset().
Reference: http://thread.gmane.org/gmane.linux.kernel.cryptoapi/13764/
Fixes:
|
||
|---|---|---|
| .. | ||
| fonts | ||
| lz4 | ||
| lzo | ||
| mpi | ||
| raid6 | ||
| reed_solomon | ||
| xz | ||
| zlib_deflate | ||
| zlib_inflate | ||
| .gitignore | ||
| argv_split.c | ||
| asn1_decoder.c | ||
| assoc_array.c | ||
| atomic64_test.c | ||
| atomic64.c | ||
| audit.c | ||
| average.c | ||
| bcd.c | ||
| bch.c | ||
| bitmap.c | ||
| bitrev.c | ||
| bsearch.c | ||
| btree.c | ||
| bug.c | ||
| build_OID_registry | ||
| bust_spinlocks.c | ||
| check_signature.c | ||
| checksum.c | ||
| clz_ctz.c | ||
| clz_tab.c | ||
| cmdline.c | ||
| compat_audit.c | ||
| cordic.c | ||
| cpu_rmap.c | ||
| cpu-notifier-error-inject.c | ||
| cpumask.c | ||
| crc-ccitt.c | ||
| crc-itu-t.c | ||
| crc-t10dif.c | ||
| crc7.c | ||
| crc8.c | ||
| crc16.c | ||
| crc32.c | ||
| crc32defs.h | ||
| ctype.c | ||
| debug_locks.c | ||
| debugobjects.c | ||
| dec_and_lock.c | ||
| decompress_bunzip2.c | ||
| decompress_inflate.c | ||
| decompress_unlz4.c | ||
| decompress_unlzma.c | ||
| decompress_unlzo.c | ||
| decompress_unxz.c | ||
| decompress.c | ||
| devres.c | ||
| digsig.c | ||
| div64.c | ||
| dma-debug.c | ||
| dump_stack.c | ||
| dynamic_debug.c | ||
| dynamic_queue_limits.c | ||
| earlycpio.c | ||
| extable.c | ||
| fault-inject.c | ||
| fdt_empty_tree.c | ||
| fdt_ro.c | ||
| fdt_rw.c | ||
| fdt_strerror.c | ||
| fdt_sw.c | ||
| fdt_wip.c | ||
| fdt.c | ||
| find_last_bit.c | ||
| find_next_bit.c | ||
| flex_array.c | ||
| flex_proportions.c | ||
| gcd.c | ||
| gen_crc32table.c | ||
| genalloc.c | ||
| glob.c | ||
| halfmd4.c | ||
| hexdump.c | ||
| hweight.c | ||
| idr.c | ||
| inflate.c | ||
| int_sqrt.c | ||
| interval_tree_test.c | ||
| interval_tree.c | ||
| iomap_copy.c | ||
| iomap.c | ||
| iommu-helper.c | ||
| ioremap.c | ||
| irq_regs.c | ||
| is_single_threaded.c | ||
| jedec_ddr_data.c | ||
| kasprintf.c | ||
| Kconfig | ||
| Kconfig.debug | ||
| Kconfig.kasan | ||
| Kconfig.kgdb | ||
| Kconfig.kmemcheck | ||
| kfifo.c | ||
| klist.c | ||
| kobject_uevent.c | ||
| kobject.c | ||
| kstrtox.c | ||
| kstrtox.h | ||
| lcm.c | ||
| libcrc32c.c | ||
| list_debug.c | ||
| list_sort.c | ||
| llist.c | ||
| locking-selftest-hardirq.h | ||
| locking-selftest-mutex.h | ||
| locking-selftest-rlock-hardirq.h | ||
| locking-selftest-rlock-softirq.h | ||
| locking-selftest-rlock.h | ||
| locking-selftest-rsem.h | ||
| locking-selftest-softirq.h | ||
| locking-selftest-spin-hardirq.h | ||
| locking-selftest-spin-softirq.h | ||
| locking-selftest-spin.h | ||
| locking-selftest-wlock-hardirq.h | ||
| locking-selftest-wlock-softirq.h | ||
| locking-selftest-wlock.h | ||
| locking-selftest-wsem.h | ||
| locking-selftest.c | ||
| lockref.c | ||
| lru_cache.c | ||
| Makefile | ||
| md5.c | ||
| memory-notifier-error-inject.c | ||
| memweight.c | ||
| net_utils.c | ||
| nlattr.c | ||
| notifier-error-inject.c | ||
| notifier-error-inject.h | ||
| of-reconfig-notifier-error-inject.c | ||
| oid_registry.c | ||
| parser.c | ||
| pci_iomap.c | ||
| percpu_counter.c | ||
| percpu_ida.c | ||
| percpu_test.c | ||
| percpu-refcount.c | ||
| plist.c | ||
| pm-notifier-error-inject.c | ||
| proportions.c | ||
| radix-tree.c | ||
| random32.c | ||
| ratelimit.c | ||
| rational.c | ||
| rbtree_test.c | ||
| rbtree.c | ||
| reciprocal_div.c | ||
| rhashtable.c | ||
| scatterlist.c | ||
| seq_buf.c | ||
| sha1.c | ||
| show_mem.c | ||
| smp_processor_id.c | ||
| sort.c | ||
| stmp_device.c | ||
| string_helpers.c | ||
| string.c | ||
| strncpy_from_user.c | ||
| strnlen_user.c | ||
| swiotlb.c | ||
| syscall.c | ||
| test_bpf.c | ||
| test_firmware.c | ||
| test_kasan.c | ||
| test_module.c | ||
| test_rhashtable.c | ||
| test_user_copy.c | ||
| test-hexdump.c | ||
| test-kstrtox.c | ||
| test-string_helpers.c | ||
| textsearch.c | ||
| timerqueue.c | ||
| ts_bm.c | ||
| ts_fsm.c | ||
| ts_kmp.c | ||
| ucs2_string.c | ||
| usercopy.c | ||
| uuid.c | ||
| vsprintf.c | ||