linux/kernel/stackleak.c
Joel Granados 78eb4ea25c sysctl: treewide: constify the ctl_table argument of proc_handlers
const qualify the struct ctl_table argument in the proc_handler function
signatures. This is a prerequisite to moving the static ctl_table
structs into .rodata data which will ensure that proc_handler function
pointers cannot be modified.

This patch has been generated by the following coccinelle script:

```
  virtual patch

  @r1@
  identifier ctl, write, buffer, lenp, ppos;
  identifier func !~ "appldata_(timer|interval)_handler|sched_(rt|rr)_handler|rds_tcp_skbuf_handler|proc_sctp_do_(hmac_alg|rto_min|rto_max|udp_port|alpha_beta|auth|probe_interval)";
  @@

  int func(
  - struct ctl_table *ctl
  + const struct ctl_table *ctl
    ,int write, void *buffer, size_t *lenp, loff_t *ppos);

  @r2@
  identifier func, ctl, write, buffer, lenp, ppos;
  @@

  int func(
  - struct ctl_table *ctl
  + const struct ctl_table *ctl
    ,int write, void *buffer, size_t *lenp, loff_t *ppos)
  { ... }

  @r3@
  identifier func;
  @@

  int func(
  - struct ctl_table *
  + const struct ctl_table *
    ,int , void *, size_t *, loff_t *);

  @r4@
  identifier func, ctl;
  @@

  int func(
  - struct ctl_table *ctl
  + const struct ctl_table *ctl
    ,int , void *, size_t *, loff_t *);

  @r5@
  identifier func, write, buffer, lenp, ppos;
  @@

  int func(
  - struct ctl_table *
  + const struct ctl_table *
    ,int write, void *buffer, size_t *lenp, loff_t *ppos);

```

* Code formatting was adjusted in xfs_sysctl.c to comply with code
  conventions. The xfs_stats_clear_proc_handler,
  xfs_panic_mask_proc_handler and xfs_deprecated_dointvec_minmax where
  adjusted.

* The ctl_table argument in proc_watchdog_common was const qualified.
  This is called from a proc_handler itself and is calling back into
  another proc_handler, making it necessary to change it as part of the
  proc_handler migration.

Co-developed-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Co-developed-by: Joel Granados <j.granados@samsung.com>
Signed-off-by: Joel Granados <j.granados@samsung.com>
2024-07-24 20:59:29 +02:00

177 lines
4.7 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>
#include <linux/init.h>
static DEFINE_STATIC_KEY_FALSE(stack_erasing_bypass);
#ifdef CONFIG_SYSCTL
static int stack_erasing_sysctl(const 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;
struct ctl_table table_copy = *table;
table_copy.data = &state;
ret = proc_dointvec_minmax(&table_copy, 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;
}
static struct ctl_table stackleak_sysctls[] = {
{
.procname = "stack_erasing",
.data = NULL,
.maxlen = sizeof(int),
.mode = 0600,
.proc_handler = stack_erasing_sysctl,
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE,
},
};
static int __init stackleak_sysctls_init(void)
{
register_sysctl_init("kernel", stackleak_sysctls);
return 0;
}
late_initcall(stackleak_sysctls_init);
#endif /* CONFIG_SYSCTL */
#define skip_erasing() static_branch_unlikely(&stack_erasing_bypass)
#else
#define skip_erasing() false
#endif /* CONFIG_STACKLEAK_RUNTIME_DISABLE */
#ifndef __stackleak_poison
static __always_inline void __stackleak_poison(unsigned long erase_low,
unsigned long erase_high,
unsigned long poison)
{
while (erase_low < erase_high) {
*(unsigned long *)erase_low = poison;
erase_low += sizeof(unsigned long);
}
}
#endif
static __always_inline void __stackleak_erase(bool on_task_stack)
{
const unsigned long task_stack_low = stackleak_task_low_bound(current);
const unsigned long task_stack_high = stackleak_task_high_bound(current);
unsigned long erase_low, erase_high;
erase_low = stackleak_find_top_of_poison(task_stack_low,
current->lowest_stack);
#ifdef CONFIG_STACKLEAK_METRICS
current->prev_lowest_stack = erase_low;
#endif
/*
* Write poison to the task's stack between 'erase_low' and
* 'erase_high'.
*
* If we're running on a different stack (e.g. an entry trampoline
* stack) we can erase everything below the pt_regs at the top of the
* task stack.
*
* If we're running on the task stack itself, we must not clobber any
* stack used by this function and its caller. We assume that this
* function has a fixed-size stack frame, and the current stack pointer
* doesn't change while we write poison.
*/
if (on_task_stack)
erase_high = current_stack_pointer;
else
erase_high = task_stack_high;
__stackleak_poison(erase_low, erase_high, STACKLEAK_POISON);
/* Reset the 'lowest_stack' value for the next syscall */
current->lowest_stack = task_stack_high;
}
/*
* Erase and poison the portion of the task stack used since the last erase.
* Can be called from the task stack or an entry stack when the task stack is
* no longer in use.
*/
asmlinkage void noinstr stackleak_erase(void)
{
if (skip_erasing())
return;
__stackleak_erase(on_thread_stack());
}
/*
* Erase and poison the portion of the task stack used since the last erase.
* Can only be called from the task stack.
*/
asmlinkage void noinstr stackleak_erase_on_task_stack(void)
{
if (skip_erasing())
return;
__stackleak_erase(true);
}
/*
* Erase and poison the portion of the task stack used since the last erase.
* Can only be called from a stack other than the task stack.
*/
asmlinkage void noinstr stackleak_erase_off_task_stack(void)
{
if (skip_erasing())
return;
__stackleak_erase(false);
}
void __used __no_caller_saved_registers noinstr 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 >= stackleak_task_low_bound(current)) {
current->lowest_stack = sp;
}
}
EXPORT_SYMBOL(stackleak_track_stack);