From 7fbe6ac02485504b964b283aca62b36b4313ca79 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Mon, 24 Oct 2016 08:31:27 -0500 Subject: [PATCH] x86/unwind: Fix empty stack dereference in guess unwinder Vince Waver reported the following bug: WARNING: CPU: 0 PID: 21338 at arch/x86/mm/fault.c:435 vmalloc_fault+0x58/0x1f0 CPU: 0 PID: 21338 Comm: perf_fuzzer Not tainted 4.8.0+ #37 Hardware name: Hewlett-Packard HP Compaq Pro 6305 SFF/1850, BIOS K06 v02.57 08/16/2013 Call Trace: ? dump_stack+0x46/0x59 ? __warn+0xd5/0xee ? vmalloc_fault+0x58/0x1f0 ? __do_page_fault+0x6d/0x48e ? perf_log_throttle+0xa4/0xf4 ? trace_page_fault+0x22/0x30 ? __unwind_start+0x28/0x42 ? perf_callchain_kernel+0x75/0xac ? get_perf_callchain+0x13a/0x1f0 ? perf_callchain+0x6a/0x6c ? perf_prepare_sample+0x71/0x2eb ? perf_event_output_forward+0x1a/0x54 ? __default_send_IPI_shortcut+0x10/0x2d ? __perf_event_overflow+0xfb/0x167 ? x86_pmu_handle_irq+0x113/0x150 ? native_read_msr+0x6/0x34 ? perf_event_nmi_handler+0x22/0x39 ? perf_ibs_nmi_handler+0x4a/0x51 ? perf_event_nmi_handler+0x22/0x39 ? nmi_handle+0x4d/0xf0 ? perf_ibs_handle_irq+0x3d1/0x3d1 ? default_do_nmi+0x3c/0xd5 ? do_nmi+0x92/0x102 ? end_repeat_nmi+0x1a/0x1e ? entry_SYSCALL_64_after_swapgs+0x12/0x4a ? entry_SYSCALL_64_after_swapgs+0x12/0x4a ? entry_SYSCALL_64_after_swapgs+0x12/0x4a ^A4---[ end trace 632723104d47d31a ]--- BUG: stack guard page was hit at ffffc90008500000 (stack is ffffc900084fc000..ffffc900084fffff) kernel stack overflow (page fault): 0000 [#1] SMP ... The NMI hit in the entry code right after setting up the stack pointer from 'cpu_current_top_of_stack', so the kernel stack was empty. The 'guess' version of __unwind_start() attempted to dereference the "top of stack" pointer, which is not actually *on* the stack. Add a check in the guess unwinder to deal with an empty stack. (The frame pointer unwinder already has such a check.) Reported-by: Vince Weaver Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Arnaldo Carvalho de Melo Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: 7c7900f89770 ("x86/unwind: Add new unwind interface and implementations") Link: http://lkml.kernel.org/r/20161024133127.e5evgeebdbohnmpb@treble Signed-off-by: Ingo Molnar --- arch/x86/kernel/unwind_guess.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/unwind_guess.c b/arch/x86/kernel/unwind_guess.c index 9298993dc8b7..2d721e533cf4 100644 --- a/arch/x86/kernel/unwind_guess.c +++ b/arch/x86/kernel/unwind_guess.c @@ -47,7 +47,14 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task, get_stack_info(first_frame, state->task, &state->stack_info, &state->stack_mask); - if (!__kernel_text_address(*first_frame)) + /* + * The caller can provide the address of the first frame directly + * (first_frame) or indirectly (regs->sp) to indicate which stack frame + * to start unwinding at. Skip ahead until we reach it. + */ + if (!unwind_done(state) && + (!on_stack(&state->stack_info, first_frame, sizeof(long)) || + !__kernel_text_address(*first_frame))) unwind_next_frame(state); } EXPORT_SYMBOL_GPL(__unwind_start); -- 2.20.1