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x86/boot: Search for RSDP in memory

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Scan memory (EBDA) for the RSDP and verify RSDP by signature and
checksum.

 [ bp:
   - Trim commit message.
   - Simplify bios_get_rsdp_addr() and cleanup mad casting.
 ]

Signed-off-by: Chao Fan <fanc.fnst@cn.fujitsu.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: bhe@redhat.com
Cc: caoj.fnst@cn.fujitsu.com
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: indou.takao@jp.fujitsu.com
Cc: Ingo Molnar <mingo@redhat.com>
Cc: kasong@redhat.com
Cc: Kees Cook <keescook@chromium.org>
Cc: msys.mizuma@gmail.com
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190123110850.12433-5-fanc.fnst@cn.fujitsu.com
This commit is contained in:
Chao Fan 2019-01-23 19:08:47 +08:00 committed by Borislav Petkov
parent 33f0df8d84
commit 93a209aaaa
1 changed files with 77 additions and 0 deletions
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77
arch/x86/boot/compressed/acpi.c
View File

@ -107,3 +107,80 @@ static acpi_physical_address efi_get_rsdp_addr(void)
#endif
return rsdp_addr;
}
static u8 compute_checksum(u8 *buffer, u32 length)
{
u8 *end = buffer + length;
u8 sum = 0;
while (buffer < end)
sum += *(buffer++);
return sum;
}
/* Search a block of memory for the RSDP signature. */
static u8 *scan_mem_for_rsdp(u8 *start, u32 length)
{
struct acpi_table_rsdp *rsdp;
u8 *address, *end;
end = start + length;
/* Search from given start address for the requested length */
for (address = start; address < end; address += ACPI_RSDP_SCAN_STEP) {
/*
* Both RSDP signature and checksum must be correct.
* Note: Sometimes there exists more than one RSDP in memory;
* the valid RSDP has a valid checksum, all others have an
* invalid checksum.
*/
rsdp = (struct acpi_table_rsdp *)address;
/* BAD Signature */
if (!ACPI_VALIDATE_RSDP_SIG(rsdp->signature))
continue;
/* Check the standard checksum */
if (compute_checksum((u8 *)rsdp, ACPI_RSDP_CHECKSUM_LENGTH))
continue;
/* Check extended checksum if table version >= 2 */
if ((rsdp->revision >= 2) &&
(compute_checksum((u8 *)rsdp, ACPI_RSDP_XCHECKSUM_LENGTH)))
continue;
/* Signature and checksum valid, we have found a real RSDP */
return address;
}
return NULL;
}
/* Search RSDP address in EBDA. */
static acpi_physical_address bios_get_rsdp_addr(void)
{
unsigned long address;
u8 *rsdp;
/* Get the location of the Extended BIOS Data Area (EBDA) */
address = *(u16 *)ACPI_EBDA_PTR_LOCATION;
address <<= 4;
/*
* Search EBDA paragraphs (EBDA is required to be a minimum of
* 1K length)
*/
if (address > 0x400) {
rsdp = scan_mem_for_rsdp((u8 *)address, ACPI_EBDA_WINDOW_SIZE);
if (rsdp)
return (acpi_physical_address)(unsigned long)rsdp;
}
/* Search upper memory: 16-byte boundaries in E0000h-FFFFFh */
rsdp = scan_mem_for_rsdp((u8 *) ACPI_HI_RSDP_WINDOW_BASE,
ACPI_HI_RSDP_WINDOW_SIZE);
if (rsdp)
return (acpi_physical_address)(unsigned long)rsdp;
return 0;
}