cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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stackprotector.h (3095B)

      1/* SPDX-License-Identifier: GPL-2.0 */
      2/*
      3 * GCC stack protector support.
      4 *
      5 * Stack protector works by putting predefined pattern at the start of
      6 * the stack frame and verifying that it hasn't been overwritten when
      7 * returning from the function.  The pattern is called stack canary
      8 * and unfortunately gcc historically required it to be at a fixed offset
      9 * from the percpu segment base.  On x86_64, the offset is 40 bytes.
     10 *
     11 * The same segment is shared by percpu area and stack canary.  On
     12 * x86_64, percpu symbols are zero based and %gs (64-bit) points to the
     13 * base of percpu area.  The first occupant of the percpu area is always
     14 * fixed_percpu_data which contains stack_canary at the appropriate
     15 * offset.  On x86_32, the stack canary is just a regular percpu
     16 * variable.
     17 *
     18 * Putting percpu data in %fs on 32-bit is a minor optimization compared to
     19 * using %gs.  Since 32-bit userspace normally has %fs == 0, we are likely
     20 * to load 0 into %fs on exit to usermode, whereas with percpu data in
     21 * %gs, we are likely to load a non-null %gs on return to user mode.
     22 *
     23 * Once we are willing to require GCC 8.1 or better for 64-bit stackprotector
     24 * support, we can remove some of this complexity.
     25 */
     26
     27#ifndef _ASM_STACKPROTECTOR_H
     28#define _ASM_STACKPROTECTOR_H 1
     29
     30#ifdef CONFIG_STACKPROTECTOR
     31
     32#include <asm/tsc.h>
     33#include <asm/processor.h>
     34#include <asm/percpu.h>
     35#include <asm/desc.h>
     36
     37#include <linux/random.h>
     38#include <linux/sched.h>
     39
     40/*
     41 * Initialize the stackprotector canary value.
     42 *
     43 * NOTE: this must only be called from functions that never return
     44 * and it must always be inlined.
     45 *
     46 * In addition, it should be called from a compilation unit for which
     47 * stack protector is disabled. Alternatively, the caller should not end
     48 * with a function call which gets tail-call optimized as that would
     49 * lead to checking a modified canary value.
     50 */
     51static __always_inline void boot_init_stack_canary(void)
     52{
     53	u64 canary;
     54	u64 tsc;
     55
     56#ifdef CONFIG_X86_64
     57	BUILD_BUG_ON(offsetof(struct fixed_percpu_data, stack_canary) != 40);
     58#endif
     59	/*
     60	 * We both use the random pool and the current TSC as a source
     61	 * of randomness. The TSC only matters for very early init,
     62	 * there it already has some randomness on most systems. Later
     63	 * on during the bootup the random pool has true entropy too.
     64	 */
     65	get_random_bytes(&canary, sizeof(canary));
     66	tsc = rdtsc();
     67	canary += tsc + (tsc << 32UL);
     68	canary &= CANARY_MASK;
     69
     70	current->stack_canary = canary;
     71#ifdef CONFIG_X86_64
     72	this_cpu_write(fixed_percpu_data.stack_canary, canary);
     73#else
     74	this_cpu_write(__stack_chk_guard, canary);
     75#endif
     76}
     77
     78static inline void cpu_init_stack_canary(int cpu, struct task_struct *idle)
     79{
     80#ifdef CONFIG_X86_64
     81	per_cpu(fixed_percpu_data.stack_canary, cpu) = idle->stack_canary;
     82#else
     83	per_cpu(__stack_chk_guard, cpu) = idle->stack_canary;
     84#endif
     85}
     86
     87#else	/* STACKPROTECTOR */
     88
     89/* dummy boot_init_stack_canary() is defined in linux/stackprotector.h */
     90
     91static inline void cpu_init_stack_canary(int cpu, struct task_struct *idle)
     92{ }
     93
     94#endif	/* STACKPROTECTOR */
     95#endif	/* _ASM_STACKPROTECTOR_H */