Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755611AbdIGTIS (ORCPT ); Thu, 7 Sep 2017 15:08:18 -0400 Received: from mail-io0-f180.google.com ([209.85.223.180]:36277 "EHLO mail-io0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754127AbdIGTIQ (ORCPT ); Thu, 7 Sep 2017 15:08:16 -0400 X-Google-Smtp-Source: AOwi7QB6Ym5vF8K0j9bZjd5RqxMDOWxdOchXiqQ1hVMivd2I9N16/z8stHVVfZxXlg287iw2+mliIk3ESuxTM1ZfyXA= MIME-Version: 1.0 In-Reply-To: <20170907173609.22696-12-tycho@docker.com> References: <20170907173609.22696-1-tycho@docker.com> <20170907173609.22696-12-tycho@docker.com> From: Kees Cook Date: Thu, 7 Sep 2017 12:08:14 -0700 X-Google-Sender-Auth: 9Wnd7Suuj136yHsp3lpmbdEcgEI Message-ID: Subject: Re: [PATCH v6 11/11] lkdtm: Add test for XPFO To: Tycho Andersen Cc: LKML , Linux-MM , "kernel-hardening@lists.openwall.com" , Marco Benatto , Juerg Haefliger Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8540 Lines: 291 On Thu, Sep 7, 2017 at 10:36 AM, Tycho Andersen wrote: > From: Juerg Haefliger > > This test simply reads from userspace memory via the kernel's linear > map. > > v6: * drop an #ifdef, just let the test fail if XPFO is not supported > * add XPFO_SMP test to try and test the case when one CPU does an xpfo > unmap of an address, that it can't be used accidentally by other > CPUs. This is very close! Thanks for the updates. :) Notes below... > > Signed-off-by: Juerg Haefliger > Signed-off-by: Tycho Andersen > Tested-by: Marco Benatto > --- > drivers/misc/Makefile | 1 + > drivers/misc/lkdtm.h | 5 ++ > drivers/misc/lkdtm_core.c | 3 + > drivers/misc/lkdtm_xpfo.c | 194 ++++++++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 203 insertions(+) > > diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile > index b0b766416306..8447b42a447d 100644 > --- a/drivers/misc/Makefile > +++ b/drivers/misc/Makefile > @@ -62,6 +62,7 @@ lkdtm-$(CONFIG_LKDTM) += lkdtm_heap.o > lkdtm-$(CONFIG_LKDTM) += lkdtm_perms.o > lkdtm-$(CONFIG_LKDTM) += lkdtm_rodata_objcopy.o > lkdtm-$(CONFIG_LKDTM) += lkdtm_usercopy.o > +lkdtm-$(CONFIG_LKDTM) += lkdtm_xpfo.o > > KCOV_INSTRUMENT_lkdtm_rodata.o := n > > diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h > index 3b4976396ec4..34a6ee37f216 100644 > --- a/drivers/misc/lkdtm.h > +++ b/drivers/misc/lkdtm.h > @@ -64,4 +64,9 @@ void lkdtm_USERCOPY_STACK_FRAME_FROM(void); > void lkdtm_USERCOPY_STACK_BEYOND(void); > void lkdtm_USERCOPY_KERNEL(void); > > +/* lkdtm_xpfo.c */ > +void lkdtm_XPFO_READ_USER(void); > +void lkdtm_XPFO_READ_USER_HUGE(void); > +void lkdtm_XPFO_SMP(void); > + > #endif > diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c > index 42d2b8e31e6b..9544e329de4b 100644 > --- a/drivers/misc/lkdtm_core.c > +++ b/drivers/misc/lkdtm_core.c > @@ -235,6 +235,9 @@ struct crashtype crashtypes[] = { > CRASHTYPE(USERCOPY_STACK_FRAME_FROM), > CRASHTYPE(USERCOPY_STACK_BEYOND), > CRASHTYPE(USERCOPY_KERNEL), > + CRASHTYPE(XPFO_READ_USER), > + CRASHTYPE(XPFO_READ_USER_HUGE), > + CRASHTYPE(XPFO_SMP), > }; > > > diff --git a/drivers/misc/lkdtm_xpfo.c b/drivers/misc/lkdtm_xpfo.c > new file mode 100644 > index 000000000000..d903063bdd0b > --- /dev/null > +++ b/drivers/misc/lkdtm_xpfo.c > @@ -0,0 +1,194 @@ > +/* > + * This is for all the tests related to XPFO (eXclusive Page Frame Ownership). > + */ > + > +#include "lkdtm.h" > + > +#include > +#include > +#include > +#include > +#include > + > +#include > +#include > + > +#define XPFO_DATA 0xdeadbeef > + > +static unsigned long do_map(unsigned long flags) > +{ > + unsigned long user_addr, user_data = XPFO_DATA; > + > + user_addr = vm_mmap(NULL, 0, PAGE_SIZE, > + PROT_READ | PROT_WRITE | PROT_EXEC, > + flags, 0); > + if (user_addr >= TASK_SIZE) { > + pr_warn("Failed to allocate user memory\n"); > + return 0; > + } > + > + if (copy_to_user((void __user *)user_addr, &user_data, > + sizeof(user_data))) { > + pr_warn("copy_to_user failed\n"); > + goto free_user; > + } > + > + return user_addr; > + > +free_user: > + vm_munmap(user_addr, PAGE_SIZE); > + return 0; > +} > + > +static unsigned long *user_to_kernel(unsigned long user_addr) > +{ > + phys_addr_t phys_addr; > + void *virt_addr; > + > + phys_addr = user_virt_to_phys(user_addr); > + if (!phys_addr) { > + pr_warn("Failed to get physical address of user memory\n"); > + return NULL; > + } > + > + virt_addr = phys_to_virt(phys_addr); > + if (phys_addr != virt_to_phys(virt_addr)) { > + pr_warn("Physical address of user memory seems incorrect\n"); > + return NULL; > + } > + > + return virt_addr; > +} > + > +static void read_map(unsigned long *virt_addr) > +{ > + pr_info("Attempting bad read from kernel address %p\n", virt_addr); > + if (*(unsigned long *)virt_addr == XPFO_DATA) > + pr_err("FAIL: Bad read succeeded?!\n"); > + else > + pr_err("FAIL: Bad read didn't fail but data is incorrect?!\n"); > +} > + > +static void read_user_with_flags(unsigned long flags) > +{ > + unsigned long user_addr, *kernel; > + > + user_addr = do_map(flags); > + if (!user_addr) { > + pr_err("FAIL: map failed\n"); > + return; > + } > + > + kernel = user_to_kernel(user_addr); > + if (!kernel) { > + pr_err("FAIL: user to kernel conversion failed\n"); > + goto free_user; > + } > + > + read_map(kernel); > + > +free_user: > + vm_munmap(user_addr, PAGE_SIZE); > +} > + > +/* Read from userspace via the kernel's linear map. */ > +void lkdtm_XPFO_READ_USER(void) > +{ > + read_user_with_flags(MAP_PRIVATE | MAP_ANONYMOUS); > +} > + > +void lkdtm_XPFO_READ_USER_HUGE(void) > +{ > + read_user_with_flags(MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB); > +} > + > +struct smp_arg { > + unsigned long *virt_addr; > + unsigned int cpu; > +}; > + > +static int smp_reader(void *parg) > +{ > + struct smp_arg *arg = parg; > + unsigned long *virt_addr; > + > + if (arg->cpu != smp_processor_id()) { > + pr_err("FAIL: scheduled on wrong CPU?\n"); > + return 0; > + } > + > + virt_addr = smp_cond_load_acquire(&arg->virt_addr, VAL != NULL); > + read_map(virt_addr); > + > + return 0; > +} > + > +#ifdef CONFIG_X86 > +#define XPFO_SMP_KILLED SIGKILL > +#elif CONFIG_ARM64 > +#define XPFO_SMP_KILLED SIGSEGV > +#else > +#error unsupported arch > +#endif This will fail the build for other architectures, so I would just do this as an single if/else: #ifdef CONFIG_ARM64 # define XPFO_SMP_KILLED SIGSEGV #else # define XPFO_SMP_KILLED SIGKILL #endif > + > +/* The idea here is to read from the kernel's map on a different thread than Comment style nit: leading /*\n please... > + * did the mapping (and thus the TLB flushing), to make sure that the page > + * faults on other cores too. > + */ > +void lkdtm_XPFO_SMP(void) > +{ > + unsigned long user_addr, *virt_addr; > + struct task_struct *thread; > + int ret; > + struct smp_arg arg; > + > + if (num_online_cpus() < 2) { > + pr_err("not enough to do a multi cpu test\n"); > + return; > + } > + > + arg.virt_addr = NULL; > + arg.cpu = (smp_processor_id() + 1) % num_online_cpus(); > + thread = kthread_create(smp_reader, &arg, "lkdtm_xpfo_test"); > + if (IS_ERR(thread)) { > + pr_err("couldn't create kthread? %ld\n", PTR_ERR(thread)); > + return; > + } > + > + kthread_bind(thread, arg.cpu); > + get_task_struct(thread); > + wake_up_process(thread); > + > + user_addr = do_map(MAP_PRIVATE | MAP_ANONYMOUS); > + if (!user_addr) > + goto kill_thread; > + > + virt_addr = user_to_kernel(user_addr); > + if (!virt_addr) { > + /* > + * let's store something that will fail, so we can unblock the > + * thread > + */ > + smp_store_release(&arg.virt_addr, &arg); > + goto free_user; > + } > + > + smp_store_release(&arg.virt_addr, virt_addr); > + > + /* there must be a better way to do this. */ > + while (1) { > + if (thread->exit_state) > + break; > + msleep_interruptible(100); > + } I don't like infinite loops. How about giving this a 1 second max runtime? > + > +free_user: > + if (user_addr) > + vm_munmap(user_addr, PAGE_SIZE); > + > +kill_thread: > + ret = kthread_stop(thread); > + if (ret != XPFO_SMP_KILLED) > + pr_err("FAIL: thread wasn't killed: %d\n", ret); > + put_task_struct(thread); > +} > -- > 2.11.0 > Otherwise it looks great, thanks! -Kees -- Kees Cook Pixel Security