From: Candle Sun <[email protected]> Though do_overwritten() follows do_nothing() in source code, the final memory address order is determined by compiler. We can't always assume address of do_overwritten() is bigger than do_nothing(). At least the Clang we are using places do_overwritten() before do_nothing() in the object. This causes the copy size in lkdtm_WRITE_KERN() is *really* big and WRITE_KERN test on ARM32 arch will fail.
Get absolute value of the address substraction for memcpy() size. Signed-off-by: Candle Sun <[email protected]> --- Changes in v2: - Use abs() in place of address comparison. --- drivers/misc/lkdtm/perms.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c index 2dede2ef658f..fbb7f4554054 100644 --- a/drivers/misc/lkdtm/perms.c +++ b/drivers/misc/lkdtm/perms.c @@ -31,13 +31,13 @@ static unsigned long ro_after_init __ro_after_init = 0x55AA5500; * This just returns to the caller. It is designed to be copied into * non-executable memory regions. */ -static void do_nothing(void) +static noinline void do_nothing(void) { return; } /* Must immediately follow do_nothing for size calculuations to work out. */ -static void do_overwritten(void) +static noinline void do_overwritten(void) { pr_info("do_overwritten wasn't overwritten!\n"); return; @@ -113,7 +113,7 @@ void lkdtm_WRITE_KERN(void) size_t size; volatile unsigned char *ptr; - size = (unsigned long)do_overwritten - (unsigned long)do_nothing; + size = (size_t)abs((uintptr_t)do_overwritten - (uintptr_t)do_nothing); ptr = (unsigned char *)do_overwritten; pr_info("attempting bad %zu byte write at %px\n", size, ptr); -- 2.17.0
