• Michael Neuling's avatar
    powerpc/tm: Check for already reclaimed tasks · a54d3a42
    Michael Neuling authored
    commit 7f821fc9 upstream.
    
    Currently we can hit a scenario where we'll tm_reclaim() twice.  This
    results in a TM bad thing exception because the second reclaim occurs
    when not in suspend mode.
    
    The scenario in which this can happen is the following.  We attempt to
    deliver a signal to userspace.  To do this we need obtain the stack
    pointer to write the signal context.  To get this stack pointer we
    must tm_reclaim() in case we need to use the checkpointed stack
    pointer (see get_tm_stackpointer()).  Normally we'd then return
    directly to userspace to deliver the signal without going through
    __switch_to().
    
    Unfortunatley, if at this point we get an error (such as a bad
    userspace stack pointer), we need to exit the process.  The exit will
    result in a __switch_to().  __switch_to() will attempt to save the
    process state which results in another tm_reclaim().  This
    tm_reclaim() now causes a TM Bad Thing exception as this state has
    already been saved and the processor is no longer in TM suspend mode.
    Whee!
    
    This patch checks the state of the MSR to ensure we are TM suspended
    before we attempt the tm_reclaim().  If we've already saved the state
    away, we should no longer be in TM suspend mode.  This has the
    additional advantage of checking for a potential TM Bad Thing
    exception.
    
    Found using syscall fuzzer.
    
    Fixes: fb09692e ("powerpc: Add reclaim and recheckpoint functions for context switching transactional memory processes")
    Signed-off-by: default avatarMichael Neuling <mikey@neuling.org>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    a54d3a42
process.c 43.6 KB