On Mon, Nov 14, 2016 at 11:02 PM, Michael Ellerman <m...@ellerman.id.au> wrote: > At least on powerpc with GCC 6, the compiler is smart enough to optimise > lkdtm_CORRUPT_STACK() into an empty function that just returns.
Sneaky. Thanks! > If we print the buffer after we've written to it that prevents the > compiler from optimising away data and the memset(). > > Signed-off-by: Michael Ellerman <m...@ellerman.id.au> Acked-by: Kees Cook <keesc...@chromium.org> Greg, can you add this to the drivers/misc? -Kees > --- > drivers/misc/lkdtm_bugs.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/misc/lkdtm_bugs.c b/drivers/misc/lkdtm_bugs.c > index 182ae1894b32..30e62dd7e7ca 100644 > --- a/drivers/misc/lkdtm_bugs.c > +++ b/drivers/misc/lkdtm_bugs.c > @@ -80,7 +80,8 @@ noinline void lkdtm_CORRUPT_STACK(void) > /* Use default char array length that triggers stack protection. */ > char data[8]; > > - memset((void *)data, 0, 64); > + memset((void *)data, 'a', 64); > + pr_info("Corrupted stack with '%16s'...\n", data); > } > > void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void) > -- > 2.7.4 > -- Kees Cook Nexus Security