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

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

diff --git a/arch/x86/include/asm/bootparam_utils.h b/arch/x86/include/asm/bootparam_utils.h
index 101eb944f13c2c8ad6b4d9af9ec8e3264fb1f5a7..f5e90a849bca6c1ab6493d03b0d7ad76a69086f9 100644 (file)
--- a/arch/x86/include/asm/bootparam_utils.h
+++ b/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)
 {
        /* 
@@ -35,21 +49,40 @@ static void sanitize_boot_params(struct boot_params *boot_params)
         * problems again.
         */
        if (boot_params->sentinel) {
-               /* fields in boot_params are left uninitialized, clear them */
-               boot_params->acpi_rsdp_addr = 0;
-               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(acpi_rsdp_addr),
+                       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));
        }
 }