cd670599b7
Impact: BIOS bug safety For pre-ACPI 3 BIOSes, pre-initialize the end of the e820 buffer just in case the BIOS returns an unchanged %ecx but without actually touching the ACPI 3 extended flags field. Signed-off-by: H. Peter Anvin <hpa@zytor.com>
141 lines
3.3 KiB
C
141 lines
3.3 KiB
C
/* -*- linux-c -*- ------------------------------------------------------- *
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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* Copyright 2007 rPath, Inc. - All Rights Reserved
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* Copyright 2009 Intel Corporation; author H. Peter Anvin
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*
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* This file is part of the Linux kernel, and is made available under
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* the terms of the GNU General Public License version 2.
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*
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* ----------------------------------------------------------------------- */
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/*
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* Memory detection code
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*/
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#include "boot.h"
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#define SMAP 0x534d4150 /* ASCII "SMAP" */
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struct e820_ext_entry {
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struct e820entry std;
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u32 ext_flags;
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} __attribute__((packed));
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static int detect_memory_e820(void)
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{
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int count = 0;
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u32 next = 0;
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u32 size, id, edi;
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u8 err;
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struct e820entry *desc = boot_params.e820_map;
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static struct e820_ext_entry buf; /* static so it is zeroed */
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/*
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* Set this here so that if the BIOS doesn't change this field
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* but still doesn't change %ecx, we're still okay...
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*/
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buf.ext_flags = 1;
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do {
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size = sizeof buf;
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/* Important: %edx and %esi are clobbered by some BIOSes,
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so they must be either used for the error output
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or explicitly marked clobbered. Given that, assume there
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is something out there clobbering %ebp and %edi, too. */
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asm("pushl %%ebp; int $0x15; popl %%ebp; setc %0"
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: "=d" (err), "+b" (next), "=a" (id), "+c" (size),
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"=D" (edi), "+m" (buf)
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: "D" (&buf), "d" (SMAP), "a" (0xe820)
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: "esi");
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/* BIOSes which terminate the chain with CF = 1 as opposed
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to %ebx = 0 don't always report the SMAP signature on
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the final, failing, probe. */
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if (err)
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break;
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/* Some BIOSes stop returning SMAP in the middle of
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the search loop. We don't know exactly how the BIOS
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screwed up the map at that point, we might have a
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partial map, the full map, or complete garbage, so
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just return failure. */
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if (id != SMAP) {
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count = 0;
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break;
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}
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/* ACPI 3.0 added the extended flags support. If bit 0
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in the extended flags is zero, we're supposed to simply
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ignore the entry -- a backwards incompatible change! */
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if (size > 20 && !(buf.ext_flags & 1))
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continue;
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*desc++ = buf.std;
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count++;
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} while (next && count < ARRAY_SIZE(boot_params.e820_map));
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return boot_params.e820_entries = count;
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}
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static int detect_memory_e801(void)
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{
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u16 ax, bx, cx, dx;
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u8 err;
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bx = cx = dx = 0;
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ax = 0xe801;
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asm("stc; int $0x15; setc %0"
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: "=m" (err), "+a" (ax), "+b" (bx), "+c" (cx), "+d" (dx));
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if (err)
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return -1;
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/* Do we really need to do this? */
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if (cx || dx) {
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ax = cx;
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bx = dx;
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}
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if (ax > 15*1024)
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return -1; /* Bogus! */
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/* This ignores memory above 16MB if we have a memory hole
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there. If someone actually finds a machine with a memory
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hole at 16MB and no support for 0E820h they should probably
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generate a fake e820 map. */
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boot_params.alt_mem_k = (ax == 15*1024) ? (dx << 6)+ax : ax;
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return 0;
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}
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static int detect_memory_88(void)
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{
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u16 ax;
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u8 err;
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ax = 0x8800;
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asm("stc; int $0x15; setc %0" : "=bcdm" (err), "+a" (ax));
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boot_params.screen_info.ext_mem_k = ax;
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return -err;
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}
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int detect_memory(void)
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{
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int err = -1;
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if (detect_memory_e820() > 0)
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err = 0;
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if (!detect_memory_e801())
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err = 0;
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if (!detect_memory_88())
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err = 0;
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return err;
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}
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