From 32518aee301064e70097e5ca93073e77f50c4c50 Mon Sep 17 00:00:00 2001 From: Sami Tolvanen Date: Thu, 6 Sep 2018 13:09:06 -0700 Subject: [PATCH] FROMLIST: scs: add support for stack usage debugging Implements CONFIG_DEBUG_STACK_USAGE for shadow stacks. When enabled, also prints out the highest shadow stack usage per process. Bug: 145210207 Change-Id: I4c085b51e1432e8d52e54126ffd8bf7b6e35b529 (am from https://lore.kernel.org/patchwork/patch/1149056/) Reviewed-by: Kees Cook Signed-off-by: Sami Tolvanen --- kernel/scs.c | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) diff --git a/kernel/scs.c b/kernel/scs.c index 5245e992c692..ad74d13f2c0f 100644 --- a/kernel/scs.c +++ b/kernel/scs.c @@ -184,6 +184,44 @@ 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(p); + unsigned long s = (unsigned long)p; + + while (p < end && READ_ONCE_NOCHECK(*p)) + p++; + + return (unsigned long)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 (%d): highest shadow stack usage: %lu bytes\n", + tsk->comm, task_pid_nr(tsk), 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) { unsigned long *magic = scs_magic(__scs_base(tsk)); @@ -200,6 +238,7 @@ 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);