x86/boot: Correct RSDP parsing with 32-bit EFI

Guenter Roeck reported triple faults of a 64-bit VM using a 32-bit OVMF
EFI image. After some singlestepping of the image in gdb, it turned out
that some of the EFI config tables were at bogus addresses. Which, as
Ard pointed out, results from using the wrong efi_config_table typedef.

So switch all EFI table pointers to unsigned longs and convert them to
the proper typedef only when accessing them. This way, the proper table
type is being used.

Shorten variable names, while at it.

Fixes: 33f0df8 ("x86/boot: Search for RSDP in the EFI tables")
Reported-by: Guenter Roeck <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Tested-by: Chao Fan <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: "H. Peter Anvin" <[email protected]>
Cc: [email protected]
Cc: Ingo Molnar <[email protected]>
Cc: [email protected]
Cc: Kees Cook <[email protected]>
Cc: [email protected]
Cc: Thomas Gleixner <[email protected]>
Cc: x86-ml <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: suryasaimadhu

arch/x86/boot/compressed/acpi.c

@@ -50,7 +50,8 @@ static acpi_physical_address efi_get_rsdp_addr(void)
 	acpi_physical_address rsdp_addr = 0;
 
 #ifdef CONFIG_EFI
-	efi_system_table_t *systab;
+	unsigned long systab, systab_tables, config_tables;
+	unsigned int nr_tables;
 	struct efi_info *ei;
 	bool efi_64;
 	int size, i;
@@ -70,46 +71,57 @@ static acpi_physical_address efi_get_rsdp_addr(void)
 
 	/* Get systab from boot params. */
 #ifdef CONFIG_X86_64
-	systab = (efi_system_table_t *)(ei->efi_systab | ((__u64)ei->efi_systab_hi<<32));
+	systab = ei->efi_systab | ((__u64)ei->efi_systab_hi << 32);
 #else
 	if (ei->efi_systab_hi || ei->efi_memmap_hi) {
 		debug_putstr("Error getting RSDP address: EFI system table located above 4GB.\n");
 		return 0;
 	}
-	systab = (efi_system_table_t *)ei->efi_systab;
+	systab = ei->efi_systab;
 #endif
 	if (!systab)
 		error("EFI system table not found.");
 
-	/*
-	 * Get EFI tables from systab.
-	 */
-	size = efi_64 ? sizeof(efi_config_table_64_t) :
-			sizeof(efi_config_table_32_t);
+	/* Handle EFI bitness properly */
+	if (efi_64) {
+		efi_system_table_64_t *stbl = (efi_system_table_64_t *)systab;
+
+		config_tables	= stbl->tables;
+		nr_tables	= stbl->nr_tables;
+		size		= sizeof(efi_config_table_64_t);
+	} else {
+		efi_system_table_32_t *stbl = (efi_system_table_32_t *)systab;
 
-	for (i = 0; i < systab->nr_tables; i++) {
+		config_tables	= stbl->tables;
+		nr_tables	= stbl->nr_tables;
+		size		= sizeof(efi_config_table_32_t);
+	}
+
+	if (!config_tables)
+		error("EFI config tables not found.");
+
+	/* Get EFI tables from systab. */
+	for (i = 0; i < nr_tables; i++) {
 		acpi_physical_address table;
-		void *config_tables;
 		efi_guid_t guid;
 
-		config_tables = (void *)(systab->tables + size * i);
+		config_tables += size;
+
 		if (efi_64) {
-			efi_config_table_64_t *tmp_table;
+			efi_config_table_64_t *tbl = (efi_config_table_64_t *)config_tables;
 
-			tmp_table = config_tables;
-			guid = tmp_table->guid;
-			table = tmp_table->table;
+			guid  = tbl->guid;
+			table = tbl->table;
 
 			if (!IS_ENABLED(CONFIG_X86_64) && table >> 32) {
 				debug_putstr("Error getting RSDP address: EFI config table located above 4GB.\n");
 				return 0;
 			}
 		} else {
-			efi_config_table_32_t *tmp_table;
+			efi_config_table_32_t *tbl = (efi_config_table_32_t *)config_tables;
 
-			tmp_table = config_tables;
-			guid = tmp_table->guid;
-			table = tmp_table->table;
+			guid  = tbl->guid;
+			table = tbl->table;
 		}
 
 		if (!(efi_guidcmp(guid, ACPI_TABLE_GUID)))