forked from Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
126 lines
3.6 KiB
126 lines
3.6 KiB
// SPDX-License-Identifier: GPL-2.0 |
|
/* |
|
* This code fills the used part of the kernel stack with a poison value |
|
* before returning to userspace. It's part of the STACKLEAK feature |
|
* ported from grsecurity/PaX. |
|
* |
|
* Author: Alexander Popov <[email protected]> |
|
* |
|
* STACKLEAK reduces the information which kernel stack leak bugs can |
|
* reveal and blocks some uninitialized stack variable attacks. |
|
*/ |
|
|
|
#include <linux/stackleak.h> |
|
#include <linux/kprobes.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 *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 notrace stackleak_erase(void) |
|
{ |
|
/* It would be nice not to have 'kstack_ptr' and 'boundary' on stack */ |
|
unsigned long kstack_ptr = current->lowest_stack; |
|
unsigned long boundary = (unsigned long)end_of_stack(current); |
|
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; |
|
|
|
/* Search for the poison value in the kernel stack */ |
|
while (kstack_ptr > boundary && poison_count <= depth) { |
|
if (*(unsigned long *)kstack_ptr == STACKLEAK_POISON) |
|
poison_count++; |
|
else |
|
poison_count = 0; |
|
|
|
kstack_ptr -= sizeof(unsigned long); |
|
} |
|
|
|
/* |
|
* One 'long int' at the bottom of the thread stack is reserved and |
|
* should not be poisoned (see CONFIG_SCHED_STACK_END_CHECK=y). |
|
*/ |
|
if (kstack_ptr == boundary) |
|
kstack_ptr += sizeof(unsigned long); |
|
|
|
#ifdef CONFIG_STACKLEAK_METRICS |
|
current->prev_lowest_stack = kstack_ptr; |
|
#endif |
|
|
|
/* |
|
* Now write the poison value to the kernel stack. Start from |
|
* 'kstack_ptr' and move up till the new 'boundary'. We assume that |
|
* the stack pointer doesn't change when we write poison. |
|
*/ |
|
if (on_thread_stack()) |
|
boundary = current_stack_pointer; |
|
else |
|
boundary = current_top_of_stack(); |
|
|
|
while (kstack_ptr < boundary) { |
|
*(unsigned long *)kstack_ptr = STACKLEAK_POISON; |
|
kstack_ptr += sizeof(unsigned long); |
|
} |
|
|
|
/* Reset the 'lowest_stack' value for the next syscall */ |
|
current->lowest_stack = current_top_of_stack() - THREAD_SIZE/64; |
|
} |
|
NOKPROBE_SYMBOL(stackleak_erase); |
|
|
|
void __used __no_caller_saved_registers notrace stackleak_track_stack(void) |
|
{ |
|
unsigned long sp = current_stack_pointer; |
|
|
|
/* |
|
* Having CONFIG_STACKLEAK_TRACK_MIN_SIZE larger than |
|
* STACKLEAK_SEARCH_DEPTH makes the poison search in |
|
* stackleak_erase() unreliable. Let's prevent that. |
|
*/ |
|
BUILD_BUG_ON(CONFIG_STACKLEAK_TRACK_MIN_SIZE > STACKLEAK_SEARCH_DEPTH); |
|
|
|
/* 'lowest_stack' should be aligned on the register width boundary */ |
|
sp = ALIGN(sp, sizeof(unsigned long)); |
|
if (sp < current->lowest_stack && |
|
sp >= (unsigned long)task_stack_page(current) + |
|
sizeof(unsigned long)) { |
|
current->lowest_stack = sp; |
|
} |
|
} |
|
EXPORT_SYMBOL(stackleak_track_stack);
|
|
|