From: Michael Ellerman Date: Tue, 15 Nov 2016 07:02:32 +0000 (+1100) Subject: lkdtm: Prevent the compiler from optimising lkdtm_CORRUPT_STACK() X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=c55d240003ae253d3057dcf93510c9bd64bb7a09;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git lkdtm: Prevent the compiler from optimising lkdtm_CORRUPT_STACK() At least on powerpc with GCC 6, the compiler is smart enough to optimise lkdtm_CORRUPT_STACK() into an empty function that just returns. 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 Acked-by: Kees Cook Signed-off-by: Greg Kroah-Hartman --- 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)