From: Josh Poimboeuf jpoimboe@redhat.com
commit 84936118bdf37bda513d4a361c38181a216427e0 upstream.
There are a handful of callers to save_stack_trace_tsk() and show_stack() which try to unwind the stack of a task other than current. In such cases, it's remotely possible that the task is running on one CPU while the unwinder is reading its stack from another CPU, causing the unwinder to see stack corruption.
These cases seem to be mostly harmless. The unwinder has checks which prevent it from following bad pointers beyond the bounds of the stack. So it's not really a bug as long as the caller understands that unwinding another task will not always succeed.
In such cases, it's possible that the unwinder may read a KASAN-poisoned region of the stack. Account for that by using READ_ONCE_NOCHECK() when reading the stack of another task.
Use READ_ONCE() when reading the stack of the current task, since KASAN warnings can still be useful for finding bugs in that case.
Reported-by: Dmitry Vyukov dvyukov@google.com Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com Cc: Andy Lutomirski luto@amacapital.net Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Petkov bp@alien8.de Cc: Brian Gerst brgerst@gmail.com Cc: Dave Jones davej@codemonkey.org.uk Cc: Denys Vlasenko dvlasenk@redhat.com Cc: H. Peter Anvin hpa@zytor.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Miroslav Benes mbenes@suse.cz Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Link: http://lkml.kernel.org/r/4c575eb288ba9f73d498dfe0acde2f58674598f1.1483978430... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Andrey Konovalov andreyknvl@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/include/asm/stacktrace.h | 5 ++++- arch/x86/kernel/unwind_frame.c | 20 ++++++++++++++++++-- 2 files changed, 22 insertions(+), 3 deletions(-)
--- a/arch/x86/include/asm/stacktrace.h +++ b/arch/x86/include/asm/stacktrace.h @@ -55,13 +55,16 @@ extern int kstack_depth_to_print; static inline unsigned long * get_frame_pointer(struct task_struct *task, struct pt_regs *regs) { + struct inactive_task_frame *frame; + if (regs) return (unsigned long *)regs->bp;
if (task == current) return __builtin_frame_address(0);
- return (unsigned long *)((struct inactive_task_frame *)task->thread.sp)->bp; + frame = (struct inactive_task_frame *)task->thread.sp; + return (unsigned long *)READ_ONCE_NOCHECK(frame->bp); } #else static inline unsigned long * --- a/arch/x86/kernel/unwind_frame.c +++ b/arch/x86/kernel/unwind_frame.c @@ -6,6 +6,21 @@
#define FRAME_HEADER_SIZE (sizeof(long) * 2)
+/* + * This disables KASAN checking when reading a value from another task's stack, + * since the other task could be running on another CPU and could have poisoned + * the stack in the meantime. + */ +#define READ_ONCE_TASK_STACK(task, x) \ +({ \ + unsigned long val; \ + if (task == current) \ + val = READ_ONCE(x); \ + else \ + val = READ_ONCE_NOCHECK(x); \ + val; \ +}) + unsigned long unwind_get_return_address(struct unwind_state *state) { unsigned long addr; @@ -14,7 +29,8 @@ unsigned long unwind_get_return_address( if (unwind_done(state)) return 0;
- addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, *addr_p, + addr = READ_ONCE_TASK_STACK(state->task, *addr_p); + addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, addr, addr_p);
return __kernel_text_address(addr) ? addr : 0; @@ -48,7 +64,7 @@ bool unwind_next_frame(struct unwind_sta if (unwind_done(state)) return false;
- next_bp = (unsigned long *)*state->bp; + next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task,*state->bp);
/* make sure the next frame's data is accessible */ if (!update_stack_state(state, next_bp, FRAME_HEADER_SIZE))