Add a copy_to_user() call to the ACCESS_USERSPACE test prior to attempting direct dereferencing of the user address to ensure the page is present. Otherwise, a fault occurs on arm kernels even prior to the introduction of CONFIG_CPU_SW_DOMAIN_PAN, and there is no difference in behavior for CONFIG_CPU_SW_DOMAIN_PAN=n vs CONFIG_CPU_SW_DOMAIN_PAN=y.
Before this change, for any value of CONFIG_CPU_SW_DOMAIN_PAN: lkdtm: Performing direct entry ACCESS_USERSPACE lkdtm: attempting bad read at b6fe8000 Unable to handle kernel paging request at virtual address b6fe8000 After this change, for CONFIG_CPU_SW_DOMAIN_PAN=n: lkdtm: Performing direct entry ACCESS_USERSPACE lkdtm: attempting bad read at b6efc000 lkdtm: attempting bad write at b6efc000 After this change, for CONFIG_CPU_SW_DOMAIN_PAN=y: lkdtm: Performing direct entry ACCESS_USERSPACE lkdtm: attempting bad read at b6f7d000 Unhandled fault: page domain fault (0x01b) at 0xb6f7d000 ... Signed-off-by: Stephen Smalley <[email protected]> --- drivers/misc/lkdtm.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c index b5abe34..11fdadc 100644 --- a/drivers/misc/lkdtm.c +++ b/drivers/misc/lkdtm.c @@ -472,7 +472,7 @@ static void lkdtm_do_action(enum ctype which) break; } case CT_ACCESS_USERSPACE: { - unsigned long user_addr, tmp; + unsigned long user_addr, tmp = 0; unsigned long *ptr; user_addr = vm_mmap(NULL, 0, PAGE_SIZE, @@ -483,6 +483,12 @@ static void lkdtm_do_action(enum ctype which) return; } + if (copy_to_user((void __user *)user_addr, &tmp, sizeof(tmp))) { + pr_warn("copy_to_user failed\n"); + vm_munmap(user_addr, PAGE_SIZE); + return; + } + ptr = (unsigned long *)user_addr; pr_info("attempting bad read at %p\n", ptr); -- 2.4.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
