• David Miller's avatar
    crypto: Work around deallocated stack frame reference gcc bug on sparc. · d41519a6
    David Miller authored
    On sparc, if we have an alloca() like situation, as is the case with
    SHASH_DESC_ON_STACK(), we can end up referencing deallocated stack
    memory.  The result can be that the value is clobbered if a trap
    or interrupt arrives at just the right instruction.
    
    It only occurs if the function ends returning a value from that
    alloca() area and that value can be placed into the return value
    register using a single instruction.
    
    For example, in lib/libcrc32c.c:crc32c() we end up with a return
    sequence like:
    
            return  %i7+8
             lduw   [%o5+16], %o0   ! MEM[(u32 *)__shash_desc.1_10 + 16B],
    
    %o5 holds the base of the on-stack area allocated for the shash
    descriptor.  But the return released the stack frame and the
    register window.
    
    So if an intererupt arrives between 'return' and 'lduw', then
    the value read at %o5+16 can be corrupted.
    
    Add a data compiler barrier to work around this problem.  This is
    exactly what the gcc fix will end up doing as well, and it absolutely
    should not change the code generated for other cpus (unless gcc
    on them has the same bug :-)
    
    With crucial insight from Eric Sandeen.
    
    Cc: <stable@vger.kernel.org>
    Reported-by: default avatarAnatoly Pugachev <matorola@gmail.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
    d41519a6