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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: afcd21dad8 ("x86/dumpstack/64: Use cpu_entry_area instead of orig_ist")
Reported-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Cyrill Gorcunov <gorcunov@gmail.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1910231950590.1852@nanos.tec.linutronix.de
This commit is contained in:
Thomas Gleixner 2019-10-23 20:05:49 +02:00
parent fe6f85ca12
commit e361362b08
1 changed files with 7 additions and 0 deletions
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7
arch/x86/kernel/dumpstack_64.c
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@ -94,6 +94,13 @@ static bool in_exception_stack(unsigned long *stack, struct stack_info *info)
BUILD_BUG_ON(N_EXCEPTION_STACKS != 6); BUILD_BUG_ON(N_EXCEPTION_STACKS != 6);
begin = (unsigned long)__this_cpu_read(cea_exception_stacks); 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); end = begin + sizeof(struct cea_exception_stacks);
/* Bail if @stack is outside the exception stack area. */ /* Bail if @stack is outside the exception stack area. */
if (stk < begin || stk >= end) if (stk < begin || stk >= end)