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scs: Add support for stack usage debugging

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Implements CONFIG_DEBUG_STACK_USAGE for shadow stacks. When enabled,
also prints out the highest shadow stack usage per process.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Will Deacon <will@kernel.org>
[will: rewrote most of scs_check_usage()]
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Sami Tolvanen 2020-04-27 09:00:09 -07:00 committed by Will Deacon
parent 628d06a48f
commit 5bbaf9d1fc
1 changed files with 29 additions and 1 deletions
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30
kernel/scs.c
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@ -63,10 +63,37 @@ int scs_prepare(struct task_struct *tsk, int node)
task_scs(tsk) = s;
task_scs_offset(tsk) = 0;
scs_account(tsk, 1);
return 0;
}
static void scs_check_usage(struct task_struct *tsk)
{
static unsigned long highest;
unsigned long *p, prev, curr = highest, used = 0;
if (!IS_ENABLED(CONFIG_DEBUG_STACK_USAGE))
return;
for (p = task_scs(tsk); p < __scs_magic(tsk); ++p) {
if (!READ_ONCE_NOCHECK(*p))
break;
used++;
}
while (used > curr) {
prev = cmpxchg_relaxed(&highest, curr, used);
if (prev == curr) {
pr_info("%s (%d): highest shadow stack usage: %lu bytes\n",
tsk->comm, task_pid_nr(tsk), used);
break;
}
curr = prev;
}
}
void scs_release(struct task_struct *tsk)
{
void *s = task_scs(tsk);
@ -75,6 +102,7 @@ void scs_release(struct task_struct *tsk)
return;
WARN(scs_corrupted(tsk), "corrupted shadow stack detected when freeing task\n");
scs_check_usage(tsk);
scs_account(tsk, -1);
scs_free(s);
}