Commits
Josh Poimboeuf committed 62dd86ac01f
x86/unwind: Fix dereference of untrusted pointer
Tetsuo Handa and Fengguang Wu reported a panic in the unwinder:
BUG: unable to handle kernel NULL pointer dereference at 000001f2
IP: update_stack_state+0xd4/0x340
*pde = 00000000
Oops: 0000 [#1] PREEMPT SMP
CPU: 0 PID: 18728 Comm: 01-cpu-hotplug Not tainted 4.13.0-rc4-00170-gb09be67 #592
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-20161025_171302-gandalf 04/01/2014
task: bb0b53c0 task.stack: bb3ac000
EIP: update_stack_state+0xd4/0x340
EFLAGS: 00010002 CPU: 0
EAX: 0000a570 EBX: bb3adccb ECX: 0000f401 EDX: 0000a570
ESI: 00000001 EDI: 000001ba EBP: bb3adc6b ESP: bb3adc3f
DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
CR0: 80050033 CR2: 000001f2 CR3: 0b3a7000 CR4: 00140690
DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
DR6: fffe0ff0 DR7: 00000400
Call Trace:
? unwind_next_frame+0xea/0x400
? __unwind_start+0xf5/0x180
? __save_stack_trace+0x81/0x160
? save_stack_trace+0x20/0x30
? __lock_acquire+0xfa5/0x12f0
? lock_acquire+0x1c2/0x230
? tick_periodic+0x3a/0xf0
? _raw_spin_lock+0x42/0x50
? tick_periodic+0x3a/0xf0
? tick_periodic+0x3a/0xf0
? debug_smp_processor_id+0x12/0x20
? tick_handle_periodic+0x23/0xc0
? local_apic_timer_interrupt+0x63/0x70
? smp_trace_apic_timer_interrupt+0x235/0x6a0
? trace_apic_timer_interrupt+0x37/0x3c
? strrchr+0x23/0x50
Code: 0f 95 c1 89 c7 89 45 e4 0f b6 c1 89 c6 89 45 dc 8b 04 85 98 cb 74 bc 88 4d e3 89 45 f0 83 c0 01 84 c9 89 04 b5 98 cb 74 bc 74 3b <8b> 47 38 8b 57 34 c6 43 1d 01 25 00 00 02 00 83 e2 03 09 d0 83
EIP: update_stack_state+0xd4/0x340 SS:ESP: 0068:bb3adc3f
CR2: 00000000000001f2
---[ end trace 0d147fd4aba8ff50 ]---
Kernel panic - not syncing: Fatal exception in interrupt
On x86-32, after decoding a frame pointer to get a regs address,
regs_size() dereferences the regs pointer when it checks regs->cs to see
if the regs are user mode. This is dangerous because it's possible that
what looks like a decoded frame pointer is actually a corrupt value, and
we don't want the unwinder to make things worse.
Instead of calling regs_size() on an unsafe pointer, just assume they're
kernel regs to start with. Later, once it's safe to access the regs, we
can do the user mode check and corresponding safety check for the
remaining two regs.
Reported-and-tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-and-tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: LKP <lkp@01.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 5ed8d8bb38c5 ("x86/unwind: Move common code into update_stack_state()")
Link: http://lkml.kernel.org/r/7f95b9a6993dec7674b3f3ab3dcd3294f7b9644d.1507597785.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>