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stackleak: Allow runtime disabling of kernel stack erasing

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Introduce CONFIG_STACKLEAK_RUNTIME_DISABLE option, which provides
'stack_erasing' sysctl. It can be used in runtime to control kernel
stack erasing for kernels built with CONFIG_GCC_PLUGIN_STACKLEAK.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Alexander Popov <alex.popov@linux.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Alexander Popov
2018-08-17 01:17:03 +03:00
committed by Kees Cook
parent ed535a2dae
commit 964c9dff00
5 changed files with 84 additions and 1 deletions
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38
kernel/stackleak.c
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@@ -12,6 +12,41 @@
#include <linux/stackleak.h>
#ifdef CONFIG_STACKLEAK_RUNTIME_DISABLE
#include <linux/jump_label.h>
#include <linux/sysctl.h>
static DEFINE_STATIC_KEY_FALSE(stack_erasing_bypass);
int stack_erasing_sysctl(struct ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
int ret = 0;
int state = !static_branch_unlikely(&stack_erasing_bypass);
int prev_state = state;
table->data = &state;
table->maxlen = sizeof(int);
ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
state = !!state;
if (ret || !write || state == prev_state)
return ret;
if (state)
static_branch_disable(&stack_erasing_bypass);
else
static_branch_enable(&stack_erasing_bypass);
pr_warn("stackleak: kernel stack erasing is %s\n",
state ? "enabled" : "disabled");
return ret;
}
#define skip_erasing() static_branch_unlikely(&stack_erasing_bypass)
#else
#define skip_erasing() false
#endif /* CONFIG_STACKLEAK_RUNTIME_DISABLE */
asmlinkage void stackleak_erase(void)
{
/* It would be nice not to have 'kstack_ptr' and 'boundary' on stack */
@@ -20,6 +55,9 @@ asmlinkage void stackleak_erase(void)
unsigned int poison_count = 0;
const unsigned int depth = STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
if (skip_erasing())
return;
/* Check that 'lowest_stack' value is sane */
if (unlikely(kstack_ptr - boundary >= THREAD_SIZE))
kstack_ptr = boundary;