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    stackprotector: use canary at end of stack to indicate overruns at oops time · 7c9f8861
    Eric Sandeen 提交于
    (Updated with a common max-stack-used checker that knows about
    the canary, as suggested by Joe Perches)
    
    Use a canary at the end of the stack to clearly indicate
    at oops time whether the stack has ever overflowed.
    
    This is a very simple implementation with a couple of
    drawbacks:
    
    1) a thread may legitimately use exactly up to the last
       word on the stack
    
     -- but the chances of doing this and then oopsing later seem slim
    
    2) it's possible that the stack usage isn't dense enough
       that the canary location could get skipped over
    
     -- but the worst that happens is that we don't flag the overrun
     -- though this happens fairly often in my testing :(
    
    With the code in place, an intentionally-bloated stack oops might
    do:
    
    BUG: unable to handle kernel paging request at ffff8103f84cc680
    IP: [<ffffffff810253df>] update_curr+0x9a/0xa8
    PGD 8063 PUD 0
    Thread overran stack or stack corrupted
    Oops: 0000 [1] SMP
    CPU 0
    ...
    
    ... unless the stack overrun is so bad that it corrupts some other
    thread.
    Signed-off-by: NEric Sandeen <sandeen@redhat.com>
    Signed-off-by: NIngo Molnar <mingo@elte.hu>
    Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
    7c9f8861
magic.h 1.6 KB