Add WRITE_OPD to check that you can't modify function descriptors. Gives the following result when function descriptors are not protected:
lkdtm: Performing direct entry WRITE_OPD lkdtm: attempting bad 16 bytes write at c00000000269b358 lkdtm: FAIL: survived bad write lkdtm: do_nothing was hijacked! Looks like a standard compiler barrier() is not enough to force GCC to use the modified function descriptor. Had to add a fake empty inline assembly to force GCC to reload the function descriptor. Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu> Acked-by: Kees Cook <keesc...@chromium.org> --- drivers/misc/lkdtm/core.c | 1 + drivers/misc/lkdtm/lkdtm.h | 1 + drivers/misc/lkdtm/perms.c | 22 ++++++++++++++++++++++ tools/testing/selftests/lkdtm/tests.txt | 1 + 4 files changed, 25 insertions(+) diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c index f69b964b9952..e2228b6fc09b 100644 --- a/drivers/misc/lkdtm/core.c +++ b/drivers/misc/lkdtm/core.c @@ -149,6 +149,7 @@ static const struct crashtype crashtypes[] = { CRASHTYPE(WRITE_RO), CRASHTYPE(WRITE_RO_AFTER_INIT), CRASHTYPE(WRITE_KERN), + CRASHTYPE(WRITE_OPD), CRASHTYPE(REFCOUNT_INC_OVERFLOW), CRASHTYPE(REFCOUNT_ADD_OVERFLOW), CRASHTYPE(REFCOUNT_INC_NOT_ZERO_OVERFLOW), diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h index d6137c70ebbe..305fc2ec3f25 100644 --- a/drivers/misc/lkdtm/lkdtm.h +++ b/drivers/misc/lkdtm/lkdtm.h @@ -106,6 +106,7 @@ void __init lkdtm_perms_init(void); void lkdtm_WRITE_RO(void); void lkdtm_WRITE_RO_AFTER_INIT(void); void lkdtm_WRITE_KERN(void); +void lkdtm_WRITE_OPD(void); void lkdtm_EXEC_DATA(void); void lkdtm_EXEC_STACK(void); void lkdtm_EXEC_KMALLOC(void); diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c index 1cf24c4a79e9..2c6aba3ff32b 100644 --- a/drivers/misc/lkdtm/perms.c +++ b/drivers/misc/lkdtm/perms.c @@ -44,6 +44,11 @@ static noinline void do_overwritten(void) return; } +static noinline void do_almost_nothing(void) +{ + pr_info("do_nothing was hijacked!\n"); +} + static void *setup_function_descriptor(func_desc_t *fdesc, void *dst) { if (!have_function_descriptors()) @@ -144,6 +149,23 @@ void lkdtm_WRITE_KERN(void) do_overwritten(); } +void lkdtm_WRITE_OPD(void) +{ + size_t size = sizeof(func_desc_t); + void (*func)(void) = do_nothing; + + if (!have_function_descriptors()) { + pr_info("XFAIL: Platform doesn't use function descriptors.\n"); + return; + } + pr_info("attempting bad %zu bytes write at %px\n", size, do_nothing); + memcpy(do_nothing, do_almost_nothing, size); + pr_err("FAIL: survived bad write\n"); + + asm("" : "=m"(func)); + func(); +} + void lkdtm_EXEC_DATA(void) { execute_location(data_area, CODE_WRITE); diff --git a/tools/testing/selftests/lkdtm/tests.txt b/tools/testing/selftests/lkdtm/tests.txt index 6b36b7f5dcf9..243c781f0780 100644 --- a/tools/testing/selftests/lkdtm/tests.txt +++ b/tools/testing/selftests/lkdtm/tests.txt @@ -44,6 +44,7 @@ ACCESS_NULL WRITE_RO WRITE_RO_AFTER_INIT WRITE_KERN +WRITE_OPD REFCOUNT_INC_OVERFLOW REFCOUNT_ADD_OVERFLOW REFCOUNT_INC_NOT_ZERO_OVERFLOW -- 2.34.1