linux-kernel - [PATCH 1/1] x86/boot: clear some fields explicitly

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Date:   Wed, 24 Jul 2019 16:15:28 -0700
From:   john.hubbard@...il.com
To:     "H . Peter Anvin" <hpa@...or.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        John Hubbard <jhubbard@...dia.com>
Subject: [PATCH 1/1] x86/boot: clear some fields explicitly

From: John Hubbard <jhubbard@...dia.com>

Recent gcc compilers (gcc 9.1) generate warnings about an
out of bounds memset, if you trying memset across several fields
of a struct. This generated a couple of warnings on x86_64 builds.

Because struct boot_params is __packed__, normal variable
variable assignment will work just as well as a memset here.
Change three u32 fields to be cleared to zero that way, and
just memset the _pad4 field.

This clears up the build warnings for me.

Signed-off-by: John Hubbard <jhubbard@...dia.com>
---
 arch/x86/include/asm/bootparam_utils.h | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/bootparam_utils.h b/arch/x86/include/asm/bootparam_utils.h
index 101eb944f13c..4df87d4a043b 100644
--- a/arch/x86/include/asm/bootparam_utils.h
+++ b/arch/x86/include/asm/bootparam_utils.h
@@ -37,12 +37,11 @@ static void sanitize_boot_params(struct boot_params *boot_params)
 	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);
+		boot_params->ext_ramdisk_image = 0;
+		boot_params->ext_ramdisk_size = 0;
+		boot_params->ext_cmd_line_ptr = 0;
+
+		memset(&boot_params->_pad4, 0, sizeof(boot_params->_pad4));
 		memset(&boot_params->_pad7[0], 0,
 		       (char *)&boot_params->edd_mbr_sig_buffer[0] -
 			(char *)&boot_params->_pad7[0]);
-- 
2.22.0