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    Subject[PATCH 5.2 128/162] x86/boot: Save fields explicitly, zero out everything else
    Date
    From: John Hubbard <jhubbard@nvidia.com>

    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 | 63 +++++++++++++++++++++++++--------
    1 file changed, 48 insertions(+), 15 deletions(-)

    --- 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
    * 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));
    }
    }


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