mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-11-01 00:48:50 +00:00
95 lines
3 KiB
C
95 lines
3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
/*
|
|
* GCC stack protector support.
|
|
*
|
|
* Stack protector works by putting predefined pattern at the start of
|
|
* the stack frame and verifying that it hasn't been overwritten when
|
|
* returning from the function. The pattern is called stack canary
|
|
* and unfortunately gcc historically required it to be at a fixed offset
|
|
* from the percpu segment base. On x86_64, the offset is 40 bytes.
|
|
*
|
|
* The same segment is shared by percpu area and stack canary. On
|
|
* x86_64, percpu symbols are zero based and %gs (64-bit) points to the
|
|
* base of percpu area. The first occupant of the percpu area is always
|
|
* fixed_percpu_data which contains stack_canary at the appropriate
|
|
* offset. On x86_32, the stack canary is just a regular percpu
|
|
* variable.
|
|
*
|
|
* Putting percpu data in %fs on 32-bit is a minor optimization compared to
|
|
* using %gs. Since 32-bit userspace normally has %fs == 0, we are likely
|
|
* to load 0 into %fs on exit to usermode, whereas with percpu data in
|
|
* %gs, we are likely to load a non-null %gs on return to user mode.
|
|
*
|
|
* Once we are willing to require GCC 8.1 or better for 64-bit stackprotector
|
|
* support, we can remove some of this complexity.
|
|
*/
|
|
|
|
#ifndef _ASM_STACKPROTECTOR_H
|
|
#define _ASM_STACKPROTECTOR_H 1
|
|
|
|
#ifdef CONFIG_STACKPROTECTOR
|
|
|
|
#include <asm/tsc.h>
|
|
#include <asm/processor.h>
|
|
#include <asm/percpu.h>
|
|
#include <asm/desc.h>
|
|
|
|
#include <linux/random.h>
|
|
#include <linux/sched.h>
|
|
|
|
/*
|
|
* Initialize the stackprotector canary value.
|
|
*
|
|
* NOTE: this must only be called from functions that never return
|
|
* and it must always be inlined.
|
|
*
|
|
* In addition, it should be called from a compilation unit for which
|
|
* stack protector is disabled. Alternatively, the caller should not end
|
|
* with a function call which gets tail-call optimized as that would
|
|
* lead to checking a modified canary value.
|
|
*/
|
|
static __always_inline void boot_init_stack_canary(void)
|
|
{
|
|
u64 canary;
|
|
u64 tsc;
|
|
|
|
#ifdef CONFIG_X86_64
|
|
BUILD_BUG_ON(offsetof(struct fixed_percpu_data, stack_canary) != 40);
|
|
#endif
|
|
/*
|
|
* We both use the random pool and the current TSC as a source
|
|
* of randomness. The TSC only matters for very early init,
|
|
* there it already has some randomness on most systems. Later
|
|
* on during the bootup the random pool has true entropy too.
|
|
*/
|
|
get_random_bytes(&canary, sizeof(canary));
|
|
tsc = rdtsc();
|
|
canary += tsc + (tsc << 32UL);
|
|
canary &= CANARY_MASK;
|
|
|
|
current->stack_canary = canary;
|
|
#ifdef CONFIG_X86_64
|
|
this_cpu_write(fixed_percpu_data.stack_canary, canary);
|
|
#else
|
|
this_cpu_write(__stack_chk_guard, canary);
|
|
#endif
|
|
}
|
|
|
|
static inline void cpu_init_stack_canary(int cpu, struct task_struct *idle)
|
|
{
|
|
#ifdef CONFIG_X86_64
|
|
per_cpu(fixed_percpu_data.stack_canary, cpu) = idle->stack_canary;
|
|
#else
|
|
per_cpu(__stack_chk_guard, cpu) = idle->stack_canary;
|
|
#endif
|
|
}
|
|
|
|
#else /* STACKPROTECTOR */
|
|
|
|
/* dummy boot_init_stack_canary() is defined in linux/stackprotector.h */
|
|
|
|
static inline void cpu_init_stack_canary(int cpu, struct task_struct *idle)
|
|
{ }
|
|
|
|
#endif /* STACKPROTECTOR */
|
|
#endif /* _ASM_STACKPROTECTOR_H */
|