From e361362b08cab1098b64b0e5fd8c879f086b3f46 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 23 Oct 2019 20:05:49 +0200 Subject: [PATCH] x86/dumpstack/64: Don't evaluate exception stacks before setup Cyrill reported the following crash: BUG: unable to handle page fault for address: 0000000000001ff0 #PF: supervisor read access in kernel mode RIP: 0010:get_stack_info+0xb3/0x148 It turns out that if the stack tracer is invoked before the exception stack mappings are initialized in_exception_stack() can erroneously classify an invalid address as an address inside of an exception stack: begin = this_cpu_read(cea_exception_stacks); <- 0 end = begin + sizeof(exception stacks); i.e. any address between 0 and end will be considered as exception stack address and the subsequent code will then try to derefence the resulting stack frame at a non mapped address. end = begin + (unsigned long)ep->size; ==> end = 0x2000 regs = (struct pt_regs *)end - 1; ==> regs = 0x2000 - sizeof(struct pt_regs *) = 0x1ff0 info->next_sp = (unsigned long *)regs->sp; ==> Crashes due to accessing 0x1ff0 Prevent this by checking the validity of the cea_exception_stack base address and bailing out if it is zero. Fixes: afcd21dad88b ("x86/dumpstack/64: Use cpu_entry_area instead of orig_ist") Reported-by: Cyrill Gorcunov Signed-off-by: Thomas Gleixner Tested-by: Cyrill Gorcunov Acked-by: Josh Poimboeuf Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1910231950590.1852@nanos.tec.linutronix.de --- arch/x86/kernel/dumpstack_64.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c index 753b8cfe8b8a..87b97897a881 100644 --- a/arch/x86/kernel/dumpstack_64.c +++ b/arch/x86/kernel/dumpstack_64.c @@ -94,6 +94,13 @@ static bool in_exception_stack(unsigned long *stack, struct stack_info *info) BUILD_BUG_ON(N_EXCEPTION_STACKS != 6); begin = (unsigned long)__this_cpu_read(cea_exception_stacks); + /* + * Handle the case where stack trace is collected _before_ + * cea_exception_stacks had been initialized. + */ + if (!begin) + return false; + end = begin + sizeof(struct cea_exception_stacks); /* Bail if @stack is outside the exception stack area. */ if (stk < begin || stk >= end)