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List:       kernel-hardening
Subject:    [kernel-hardening] Re: [PATCH RFC v5 2/5] gcc-plugins: Add STACKLEAK plugin for tracking the kernel 
From:       Alexander Popov <alex.popov () linux ! com>
Date:       2017-10-30 18:06:30
Message-ID: 586ee584-df0d-3c82-a254-16ac1573255a () linux ! com
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Hello Peter,

Thanks for your reply.

On 30.10.2017 20:32, Peter Zijlstra wrote:
> On Mon, Oct 30, 2017 at 07:51:33PM +0300, Alexander Popov wrote:
>> When the thread stack is exhausted, this BUG() is hit. But do_error_trap(),
>> which handles the exception, calls track_stack() itself again (since it is
>> instrumented by the gcc plugin). So this recursion proceeds with exhausting the
>> thread stack.
> 
> Add a __attribute__((nostacktrack)) on it?

Yes, I already tried some blacklisting in the plugin, but it didn't really help,
because:

1. there are other (more than 5) instrumented functions, that are called during
BUG() handling too;

2. decreasing CONFIG_STACKLEAK_TRACK_MIN_SIZE would add more instrumented
functions, which should be manually blacklisted (not good).

I guess handling BUG() in another stack would be a solution. For example, Andy
Lutomirski calls handle_stack_overflow in the DOUBLEFAULT_STACK
(arch/x86/mm/fault.c). Should I do something similar?

Thanks!

Best regards,
Alexander
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