4773ef33fc
Commit32927393dc("sysctl: pass kernel pointers to ->proc_handler") changed ctl_table.proc_handler to take a kernel pointer. Adjust the signature of stack_erasing_sysctl to match ctl_table.proc_handler which fixes the following sparse warning: kernel/stackleak.c:31:50: warning: incorrect type in argument 3 (different address spaces) kernel/stackleak.c:31:50: expected void * kernel/stackleak.c:31:50: got void [noderef] __user *buffer Fixes:32927393dc("sysctl: pass kernel pointers to ->proc_handler") Signed-off-by: Tobias Klauser <tklauser@distanz.ch> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Al Viro <viro@zeniv.linux.org.uk> Link: https://lkml.kernel.org/r/20200907093253.13656-1-tklauser@distanz.ch Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
127 lines
3.6 KiB
C
127 lines
3.6 KiB
C
// 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 <alex.popov@linux.com>
|
|
*
|
|
* 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);
|