cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
Log | Files | Refs | README | LICENSE | sfeed.txt

bootflag.c (1712B)

      1// SPDX-License-Identifier: GPL-2.0
      2/*
      3 *	Implement 'Simple Boot Flag Specification 2.0'
      4 */
      5#include <linux/types.h>
      6#include <linux/kernel.h>
      7#include <linux/init.h>
      8#include <linux/string.h>
      9#include <linux/spinlock.h>
     10#include <linux/acpi.h>
     11#include <asm/io.h>
     12
     13#include <linux/mc146818rtc.h>
     14
     15#define SBF_RESERVED (0x78)
     16#define SBF_PNPOS    (1<<0)
     17#define SBF_BOOTING  (1<<1)
     18#define SBF_DIAG     (1<<2)
     19#define SBF_PARITY   (1<<7)
     20
     21int sbf_port __initdata = -1;	/* set via acpi_boot_init() */
     22
     23static int __init parity(u8 v)
     24{
     25	int x = 0;
     26	int i;
     27
     28	for (i = 0; i < 8; i++) {
     29		x ^= (v & 1);
     30		v >>= 1;
     31	}
     32
     33	return x;
     34}
     35
     36static void __init sbf_write(u8 v)
     37{
     38	unsigned long flags;
     39
     40	if (sbf_port != -1) {
     41		v &= ~SBF_PARITY;
     42		if (!parity(v))
     43			v |= SBF_PARITY;
     44
     45		printk(KERN_INFO "Simple Boot Flag at 0x%x set to 0x%x\n",
     46			sbf_port, v);
     47
     48		spin_lock_irqsave(&rtc_lock, flags);
     49		CMOS_WRITE(v, sbf_port);
     50		spin_unlock_irqrestore(&rtc_lock, flags);
     51	}
     52}
     53
     54static u8 __init sbf_read(void)
     55{
     56	unsigned long flags;
     57	u8 v;
     58
     59	if (sbf_port == -1)
     60		return 0;
     61
     62	spin_lock_irqsave(&rtc_lock, flags);
     63	v = CMOS_READ(sbf_port);
     64	spin_unlock_irqrestore(&rtc_lock, flags);
     65
     66	return v;
     67}
     68
     69static int __init sbf_value_valid(u8 v)
     70{
     71	if (v & SBF_RESERVED)		/* Reserved bits */
     72		return 0;
     73	if (!parity(v))
     74		return 0;
     75
     76	return 1;
     77}
     78
     79static int __init sbf_init(void)
     80{
     81	u8 v;
     82
     83	if (sbf_port == -1)
     84		return 0;
     85
     86	v = sbf_read();
     87	if (!sbf_value_valid(v)) {
     88		printk(KERN_WARNING "Simple Boot Flag value 0x%x read from "
     89			"CMOS RAM was invalid\n", v);
     90	}
     91
     92	v &= ~SBF_RESERVED;
     93	v &= ~SBF_BOOTING;
     94	v &= ~SBF_DIAG;
     95#if defined(CONFIG_ISAPNP)
     96	v |= SBF_PNPOS;
     97#endif
     98	sbf_write(v);
     99
    100	return 0;
    101}
    102arch_initcall(sbf_init);