| Message ID | 20191031164637.48901-8-samitolvanen@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | add support for Clang's Shadow Call Stack | expand |
On Thu, Oct 31, 2019 at 09:46:27AM -0700, samitolvanen@google.com wrote: > Implements CONFIG_DEBUG_STACK_USAGE for shadow stacks. Did I miss it, or is there no Kconfig section for this? I just realized I can't find it. I was going to say "this commit log should explain why/when this option is used", but then figured it might be explained in the Kconfig ... but I couldn't find it. ;) -Kees > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > --- > kernel/scs.c | 39 +++++++++++++++++++++++++++++++++++++++ > 1 file changed, 39 insertions(+) > > diff --git a/kernel/scs.c b/kernel/scs.c > index 7780fc4e29ac..67c43af627d1 100644 > --- a/kernel/scs.c > +++ b/kernel/scs.c > @@ -167,6 +167,44 @@ int scs_prepare(struct task_struct *tsk, int node) > return 0; > } > > +#ifdef CONFIG_DEBUG_STACK_USAGE > +static inline unsigned long scs_used(struct task_struct *tsk) > +{ > + unsigned long *p = __scs_base(tsk); > + unsigned long *end = scs_magic(tsk); > + uintptr_t s = (uintptr_t)p; > + > + while (p < end && *p) > + p++; > + > + return (uintptr_t)p - s; > +} > + > +static void scs_check_usage(struct task_struct *tsk) > +{ > + static DEFINE_SPINLOCK(lock); > + static unsigned long highest; > + unsigned long used = scs_used(tsk); > + > + if (used <= highest) > + return; > + > + spin_lock(&lock); > + > + if (used > highest) { > + pr_info("%s: highest shadow stack usage %lu bytes\n", > + __func__, used); > + highest = used; > + } > + > + spin_unlock(&lock); > +} > +#else > +static inline void scs_check_usage(struct task_struct *tsk) > +{ > +} > +#endif > + > bool scs_corrupted(struct task_struct *tsk) > { > return *scs_magic(tsk) != SCS_END_MAGIC; > @@ -181,6 +219,7 @@ void scs_release(struct task_struct *tsk) > return; > > WARN_ON(scs_corrupted(tsk)); > + scs_check_usage(tsk); > > scs_account(tsk, -1); > task_set_scs(tsk, NULL); > -- > 2.24.0.rc0.303.g954a862665-goog >
On Thu, Oct 31, 2019 at 8:55 PM Kees Cook <keescook@chromium.org> wrote: > > On Thu, Oct 31, 2019 at 09:46:27AM -0700, samitolvanen@google.com wrote: > > Implements CONFIG_DEBUG_STACK_USAGE for shadow stacks. > > Did I miss it, or is there no Kconfig section for this? I just realized > I can't find it. I was going to say "this commit log should explain > why/when this option is used", but then figured it might be explained in > the Kconfig ... but I couldn't find it. ;) It's in lib/Kconfig.debug. But yes, I will add a commit message in v4. Sami
On Fri, Nov 01, 2019 at 09:32:54AM -0700, Sami Tolvanen wrote: > On Thu, Oct 31, 2019 at 8:55 PM Kees Cook <keescook@chromium.org> wrote: > > > > On Thu, Oct 31, 2019 at 09:46:27AM -0700, samitolvanen@google.com wrote: > > > Implements CONFIG_DEBUG_STACK_USAGE for shadow stacks. > > > > Did I miss it, or is there no Kconfig section for this? I just realized > > I can't find it. I was going to say "this commit log should explain > > why/when this option is used", but then figured it might be explained in > > the Kconfig ... but I couldn't find it. ;) > > It's in lib/Kconfig.debug. But yes, I will add a commit message in v4. Oh duh -- it's an existing option. Cool; I'm all good. :)
diff --git a/kernel/scs.c b/kernel/scs.c index 7780fc4e29ac..67c43af627d1 100644 --- a/kernel/scs.c +++ b/kernel/scs.c @@ -167,6 +167,44 @@ int scs_prepare(struct task_struct *tsk, int node) return 0; } +#ifdef CONFIG_DEBUG_STACK_USAGE +static inline unsigned long scs_used(struct task_struct *tsk) +{ + unsigned long *p = __scs_base(tsk); + unsigned long *end = scs_magic(tsk); + uintptr_t s = (uintptr_t)p; + + while (p < end && *p) + p++; + + return (uintptr_t)p - s; +} + +static void scs_check_usage(struct task_struct *tsk) +{ + static DEFINE_SPINLOCK(lock); + static unsigned long highest; + unsigned long used = scs_used(tsk); + + if (used <= highest) + return; + + spin_lock(&lock); + + if (used > highest) { + pr_info("%s: highest shadow stack usage %lu bytes\n", + __func__, used); + highest = used; + } + + spin_unlock(&lock); +} +#else +static inline void scs_check_usage(struct task_struct *tsk) +{ +} +#endif + bool scs_corrupted(struct task_struct *tsk) { return *scs_magic(tsk) != SCS_END_MAGIC; @@ -181,6 +219,7 @@ void scs_release(struct task_struct *tsk) return; WARN_ON(scs_corrupted(tsk)); + scs_check_usage(tsk); scs_account(tsk, -1); task_set_scs(tsk, NULL);
Implements CONFIG_DEBUG_STACK_USAGE for shadow stacks. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> --- kernel/scs.c | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+)