x86/boot: Save fields explicitly, zero out everything else

commit a90118c445cc7f07781de26a9684d4ec58bfcfd1 upstream.

Recent gcc compilers (gcc 9.1) generate warnings about an out of bounds
memset, if the memset goes accross several fields of a struct. This
generated a couple of warnings on x86_64 builds in sanitize_boot_params().

Fix this by explicitly saving the fields in struct boot_params
that are intended to be preserved, and zeroing all the rest.

[ tglx: Tagged for stable as it breaks the warning free build there as well ]

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Suggested-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20190731054627.5627-2-jhubbard@nvidia.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/include/asm/bootparam_utils.h

@@ -18,6 +18,20 @@
  * Note: efi_info is commonly left uninitialized, but that field has a
  * private magic, so it is better to leave it unchanged.
  */
+
+#define sizeof_mbr(type, member) ({ sizeof(((type *)0)->member); })
+
+#define BOOT_PARAM_PRESERVE(struct_member)				\
+	{								\
+		.start = offsetof(struct boot_params, struct_member),	\
+		.len   = sizeof_mbr(struct boot_params, struct_member),	\
+	}
+
+struct boot_params_to_save {
+	unsigned int start;
+	unsigned int len;
+};
+
 static void sanitize_boot_params(struct boot_params *boot_params)
 {
 	/* 
@@ -36,19 +50,39 @@ static void sanitize_boot_params(struct boot_params *boot_params)
 	 */
 	if (boot_params->sentinel) {
 		/* fields in boot_params are left uninitialized, clear them */
-		memset(&boot_params->ext_ramdisk_image, 0,
-		       (char *)&boot_params->efi_info -
-			(char *)&boot_params->ext_ramdisk_image);
-		memset(&boot_params->kbd_status, 0,
-		       (char *)&boot_params->hdr -
-		       (char *)&boot_params->kbd_status);
-		memset(&boot_params->_pad7[0], 0,
-		       (char *)&boot_params->edd_mbr_sig_buffer[0] -
-			(char *)&boot_params->_pad7[0]);
-		memset(&boot_params->_pad8[0], 0,
-		       (char *)&boot_params->eddbuf[0] -
-			(char *)&boot_params->_pad8[0]);
-		memset(&boot_params->_pad9[0], 0, sizeof(boot_params->_pad9));
+		static struct boot_params scratch;
+		char *bp_base = (char *)boot_params;
+		char *save_base = (char *)&scratch;
+		int i;
+
+		const struct boot_params_to_save to_save[] = {
+			BOOT_PARAM_PRESERVE(screen_info),
+			BOOT_PARAM_PRESERVE(apm_bios_info),
+			BOOT_PARAM_PRESERVE(tboot_addr),
+			BOOT_PARAM_PRESERVE(ist_info),
+			BOOT_PARAM_PRESERVE(hd0_info),
+			BOOT_PARAM_PRESERVE(hd1_info),
+			BOOT_PARAM_PRESERVE(sys_desc_table),
+			BOOT_PARAM_PRESERVE(olpc_ofw_header),
+			BOOT_PARAM_PRESERVE(efi_info),
+			BOOT_PARAM_PRESERVE(alt_mem_k),
+			BOOT_PARAM_PRESERVE(scratch),
+			BOOT_PARAM_PRESERVE(e820_entries),
+			BOOT_PARAM_PRESERVE(eddbuf_entries),
+			BOOT_PARAM_PRESERVE(edd_mbr_sig_buf_entries),
+			BOOT_PARAM_PRESERVE(edd_mbr_sig_buffer),
+			BOOT_PARAM_PRESERVE(e820_table),
+			BOOT_PARAM_PRESERVE(eddbuf),
+		};
+
+		memset(&scratch, 0, sizeof(scratch));
+
+		for (i = 0; i < ARRAY_SIZE(to_save); i++) {
+			memcpy(save_base + to_save[i].start,
+			       bp_base + to_save[i].start, to_save[i].len);
+		}
+
+		memcpy(boot_params, save_base, sizeof(*boot_params));
 	}
 }