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 <gorcu...@gmail.com>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Tested-by: Cyrill Gorcunov <gorcu...@gmail.com>
Cc: sta...@vger.kernel.org
---
arch/x86/kernel/dumpstack_64.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -94,6 +94,13 @@ static bool in_exception_stack(unsigned
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)
