x86/boot: Search for RSDP in memory

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

diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c
index 5559fde1c0fef5d3d58e5006afd4a7f7243df0fb..66bda1b5cf946caaabd1e3fad64adbe0ffd0ad83 100644 (file)
--- a/arch/x86/boot/compressed/acpi.c
+++ b/arch/x86/boot/compressed/acpi.c
@@ -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;
+}