Re: [PATCH RFC v9 0/7] Introduce the STACKLEAK feature and a test for it
On Mon, Mar 5, 2018 at 11:42 AM, Dave Hansenwrote: > On 03/05/2018 11:34 AM, Kees Cook wrote: >> Boris, Andy, and Dave (Hansen), you've all looked at this; would you >> be willing to give an Ack on the x86 parts? (Though I do now see a new >> comment from Dave was just sent.) And if not, what changes would you >> like to see? > > I think it could definitely use another cleanup and de-#ifdef'ing pass. > It seems to have inherited the style from the original code and it's a > bit more than we're used to in mainline. There are a few places it could be minimized, that's true. It looked like it might not be worth it, but the places I see are: include/linux/compiler.h: +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK +/* Poison value points to the unused hole in the virtual memory map */ +# define STACKLEAK_POISON -0xBEEF +# define STACKLEAK_POISON_CHECK_DEPTH 128 +#endif This doesn't need an #ifdef wrapper... arch/x86/kernel/process_64.c and arch/x86/kernel/process_32.c: +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK + p->thread.lowest_stack = (unsigned long)task_stack_page(p) + + 2 * sizeof(unsigned long); +#endif This could be made into a helper function, maybe, in processor.h? Like: #ifdef CONFIG_GCC_PLUGIN_STACKLEAK # define record_lowest_stack(p) do { \ p->thread.lowest_stack = (unsigned long)task_stack_page(p) + 2 * sizeof(unsigned long); } while (0) #else # define save_lowest_stack(p) do { } while (0) #endif And the uses in process_*.c would be: save_lowest_stack(p); ? And "fs/proc: Show STACKLEAK metrics in the /proc file system" could maybe be adjusted too? It doesn't seem like a lot of savings, but what do you think? One new thing did pop out at me in this review, track_stack() likely shouldn't live in fs/exec.c. It has nothing to do with exec(). There aren't a lot of good places, but maybe a better place would be mm/util.c. (A whole new source file seems like overkill.) -Kees -- Kees Cook Pixel Security
Re: [PATCH RFC v9 0/7] Introduce the STACKLEAK feature and a test for it
On Mon, Mar 5, 2018 at 11:42 AM, Dave Hansen wrote: > On 03/05/2018 11:34 AM, Kees Cook wrote: >> Boris, Andy, and Dave (Hansen), you've all looked at this; would you >> be willing to give an Ack on the x86 parts? (Though I do now see a new >> comment from Dave was just sent.) And if not, what changes would you >> like to see? > > I think it could definitely use another cleanup and de-#ifdef'ing pass. > It seems to have inherited the style from the original code and it's a > bit more than we're used to in mainline. There are a few places it could be minimized, that's true. It looked like it might not be worth it, but the places I see are: include/linux/compiler.h: +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK +/* Poison value points to the unused hole in the virtual memory map */ +# define STACKLEAK_POISON -0xBEEF +# define STACKLEAK_POISON_CHECK_DEPTH 128 +#endif This doesn't need an #ifdef wrapper... arch/x86/kernel/process_64.c and arch/x86/kernel/process_32.c: +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK + p->thread.lowest_stack = (unsigned long)task_stack_page(p) + + 2 * sizeof(unsigned long); +#endif This could be made into a helper function, maybe, in processor.h? Like: #ifdef CONFIG_GCC_PLUGIN_STACKLEAK # define record_lowest_stack(p) do { \ p->thread.lowest_stack = (unsigned long)task_stack_page(p) + 2 * sizeof(unsigned long); } while (0) #else # define save_lowest_stack(p) do { } while (0) #endif And the uses in process_*.c would be: save_lowest_stack(p); ? And "fs/proc: Show STACKLEAK metrics in the /proc file system" could maybe be adjusted too? It doesn't seem like a lot of savings, but what do you think? One new thing did pop out at me in this review, track_stack() likely shouldn't live in fs/exec.c. It has nothing to do with exec(). There aren't a lot of good places, but maybe a better place would be mm/util.c. (A whole new source file seems like overkill.) -Kees -- Kees Cook Pixel Security
Re: [PATCH RFC v9 0/7] Introduce the STACKLEAK feature and a test for it
On 03/05/2018 11:34 AM, Kees Cook wrote: > Boris, Andy, and Dave (Hansen), you've all looked at this; would you > be willing to give an Ack on the x86 parts? (Though I do now see a new > comment from Dave was just sent.) And if not, what changes would you > like to see? I think it could definitely use another cleanup and de-#ifdef'ing pass. It seems to have inherited the style from the original code and it's a bit more than we're used to in mainline.
Re: [PATCH RFC v9 0/7] Introduce the STACKLEAK feature and a test for it
On 03/05/2018 11:34 AM, Kees Cook wrote: > Boris, Andy, and Dave (Hansen), you've all looked at this; would you > be willing to give an Ack on the x86 parts? (Though I do now see a new > comment from Dave was just sent.) And if not, what changes would you > like to see? I think it could definitely use another cleanup and de-#ifdef'ing pass. It seems to have inherited the style from the original code and it's a bit more than we're used to in mainline.
Re: [PATCH RFC v9 0/7] Introduce the STACKLEAK feature and a test for it
On Sat, Mar 3, 2018 at 12:00 PM, Alexander Popovwrote: > This is the 9th version of the patch series introducing STACKLEAK to the > mainline kernel. STACKLEAK is a security feature developed by Grsecurity/PaX > (kudos to them), which: > - reduces the information that can be revealed through kernel stack leak > bugs; > - blocks some uninitialized stack variable attacks (e.g. CVE-2017-17712, > CVE-2010-2963); > - introduces some runtime checks for kernel stack overflow detection. Thanks for continuing to chip away at this! I wonder if it's time to drop the "RFC" part of this? It seems like this should be ready to land pretty soon. I can start carrying this in the kspp -next tree, for example. I'd like to get some sign-off from x86, though. Boris, Andy, and Dave (Hansen), you've all looked at this; would you be willing to give an Ack on the x86 parts? (Though I do now see a new comment from Dave was just sent.) And if not, what changes would you like to see? -Kees -- Kees Cook Pixel Security
Re: [PATCH RFC v9 0/7] Introduce the STACKLEAK feature and a test for it
On Sat, Mar 3, 2018 at 12:00 PM, Alexander Popov wrote: > This is the 9th version of the patch series introducing STACKLEAK to the > mainline kernel. STACKLEAK is a security feature developed by Grsecurity/PaX > (kudos to them), which: > - reduces the information that can be revealed through kernel stack leak > bugs; > - blocks some uninitialized stack variable attacks (e.g. CVE-2017-17712, > CVE-2010-2963); > - introduces some runtime checks for kernel stack overflow detection. Thanks for continuing to chip away at this! I wonder if it's time to drop the "RFC" part of this? It seems like this should be ready to land pretty soon. I can start carrying this in the kspp -next tree, for example. I'd like to get some sign-off from x86, though. Boris, Andy, and Dave (Hansen), you've all looked at this; would you be willing to give an Ack on the x86 parts? (Though I do now see a new comment from Dave was just sent.) And if not, what changes would you like to see? -Kees -- Kees Cook Pixel Security