linux-kernel - Re: Revert commit 5dcd14ecd4 - breaks EFI boot with SLES11 elilo.efi

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Date:	Wed, 6 Mar 2013 11:53:50 -0500
From:	Josh Boyer <jwboyer@...il.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Robin Holt <holt@....com>,
	hpa@....com, linux-kernel@...r.kernel.org, pjones@...hat.com
Subject: Re: Revert commit 5dcd14ecd4 - breaks EFI boot with SLES11 elilo.efi

On Tue, Mar 5, 2013 at 2:12 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Tue, Mar 5, 2013 at 7:22 AM, H. Peter Anvin <hpa@...or.com> wrote:
>> Yes, please do the analysis I asked for.
>
> it uses first 2 pages in bzImage to bootparams.
>
> then update the fields with ===> X
>
> struct boot_params {
>         struct screen_info screen_info;                 /* 0x000 */   ===> X
>         struct apm_bios_info apm_bios_info;             /* 0x040 */   ===> X
>         __u8  _pad2[4];                                 /* 0x054 */
>         __u64  tboot_addr;                              /* 0x058 */
>         struct ist_info ist_info;                       /* 0x060 */
>         __u8  _pad3[16];                                /* 0x070 */
>         __u8  hd0_info[16];     /* obsolete! */         /* 0x080 */   ===> X
>         __u8  hd1_info[16];     /* obsolete! */         /* 0x090 */   ===> X
>         struct sys_desc_table sys_desc_table;           /* 0x0a0 */   ===> X
>         struct olpc_ofw_header olpc_ofw_header;         /* 0x0b0 */
>         __u32 ext_ramdisk_image;                        /* 0x0c0 */
>         __u32 ext_ramdisk_size;                         /* 0x0c4 */
>         __u32 ext_cmd_line_ptr;                         /* 0x0c8 */
>         __u8  _pad4[116];                               /* 0x0cc */
>         struct edid_info edid_info;                     /* 0x140 */
>         struct efi_info efi_info;                       /* 0x1c0 */   ===> X
>         __u32 alt_mem_k;                                /* 0x1e0 */   ===> X
>         __u32 scratch;          /* Scratch field! */    /* 0x1e4 */
>         __u8  e820_entries;                             /* 0x1e8 */  ===> X
>         __u8  eddbuf_entries;                           /* 0x1e9 */
>         __u8  edd_mbr_sig_buf_entries;                  /* 0x1ea */
>         __u8  kbd_status;                               /* 0x1eb */
>         __u8  _pad5[3];                                 /* 0x1ec */
>         /*
>          * The sentinel is set to a nonzero value (0xff) in header.S.
>          *
>          * A bootloader is supposed to only take setup_header and put
>          * it into a clean boot_params buffer. If it turns out that
>          * it is clumsy or too generous with the buffer, it most
>          * probably will pick up the sentinel variable too. The fact
>          * that this variable then is still 0xff will let kernel
>          * know that some variables in boot_params are invalid and
>          * kernel should zero out certain portions of boot_params.
>          */
>         __u8  sentinel;                                 /* 0x1ef */
>         __u8  _pad6[1];                                 /* 0x1f0 */
>         struct setup_header hdr;    /* setup header */  /* 0x1f1 */  ===> X
>         __u8  _pad7[0x290-0x1f1-sizeof(struct setup_header)];
>         __u32 edd_mbr_sig_buffer[EDD_MBR_SIG_MAX];      /* 0x290 */
>         struct e820entry e820_map[E820MAX];             /* 0x2d0 */  ===> X
>         __u8  _pad8[48];                                /* 0xcd0 */
>         struct edd_info eddbuf[EDDMAXNR];               /* 0xd00 */
>         __u8  _pad9[276];                               /* 0xeec */
>
> so sentinel will be kept as 0xff, so efi_info get cleared by kernel...
>
> Attached patches should avoid the clearing of efi_info when elilo is used.
>
> Do we need to clear edd and pad2 and pad3 for elilo?

I don't think this is limited to elilo.  I have a UEFI machine booting
with grub2 that also fails to boot because of this patch.  I was in the
middle of bisecting when I found this thread and if I revert 5dcd14ecd4
the machine boots again.  Put that commit back in and it doesn't.  We've
had three other reports in Fedora of similar cases.

I discussed this with Peter Jones this morning.  He was looking into what
grub2 does for boot_params and it seems to be read-modify-write instead
of clearing the whole thing.  (CC'd Peter now.)

The patch for elilo probably works, but if grub2 is hitting this then I'm
curious if most bootloaders will.  I'll finish my bisect just to be extra
sure, but something probably needs to be done in a more generic fashion
here.

josh
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