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

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Message-ID: <B7DC31CA-E378-445A-A937-1B99490C77B4@zytor.com>
Date:   Wed, 24 Jul 2019 19:12:33 -0700
From:   hpa@...or.com
To:     john.hubbard@...il.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: Re: [PATCH 1/1] x86/boot: clear some fields explicitly

On July 24, 2019 4:15:28 PM PDT, john.hubbard@...il.com wrote:
>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]);

The problem with this is that it will break silently when changes are made to this structure.

So, that is a NAK from me.
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.