x86/microcode: Do not access the initrd after it has been freed
When we look for microcode blobs, we first try builtin and if that
doesn't succeed, we fallback to the initrd supplied to the kernel.
However, at some point doing boot, that initrd gets jettisoned and we
shouldn't access it anymore. But we do, as the below KASAN report shows.
That's because find_microcode_in_initrd() doesn't check whether the
initrd is still valid or not.
So do that.
==================================================================
BUG: KASAN: use-after-free in find_cpio_data
Read of size 1 by task swapper/1/0
page:ffffea0000db9d40 count:0 mapcount:0 mapping: (null) index:0x1
flags: 0x100000000000000()
raw: 0100000000000000 0000000000000000 0000000000000001 00000000ffffffff
raw: dead000000000100 dead000000000200 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected
CPU: 1 PID: 0 Comm: swapper/1 Tainted: G W 4.10.0-rc5-debug-00075-g2dbde22 #3
Hardware name: Dell Inc. XPS 13 9360/0839Y6, BIOS 1.2.3 12/01/2016
Call Trace:
dump_stack
? _atomic_dec_and_lock
? __dump_page
kasan_report_error
? pointer
? find_cpio_data
__asan_report_load1_noabort
? find_cpio_data
find_cpio_data
? vsprintf
? dump_stack
? get_ucode_user
? print_usage_bug
find_microcode_in_initrd
__load_ucode_intel
? collect_cpu_info_early
? debug_check_no_locks_freed
load_ucode_intel_ap
? collect_cpu_info
? trace_hardirqs_on
? flat_send_IPI_mask_allbutself
load_ucode_ap
? get_builtin_firmware
? flush_tlb_func
? do_raw_spin_trylock
? cpumask_weight
cpu_init
? trace_hardirqs_off
? play_dead_common
? native_play_dead
? hlt_play_dead
? syscall_init
? arch_cpu_idle_dead
? do_idle
start_secondary
start_cpu
Memory state around the buggy address:
ffff880036e74f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff880036e74f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff880036e75000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff880036e75080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff880036e75100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Tested-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170126165833.evjemhbqzaepirxo@pd.tnic
Signed-off-by: Ingo Molnar <mingo@kernel.org>
24c2503255