kexec and struct boot_params

Hi Eric,

Could you give a list of struct boot_params field which are initialized properly by kexec? I think we need to do the sentinel hack, and want to know what to whitelist.

Also, does kexec set a bootloader ID?

Quoted 5 lines · H. Peter Anvin

Hi Eric,

Could you give a list of struct boot_params field which are initialized properly by kexec? I think we need to do the sentinel hack, and want to know what to whitelist.

the one with *
? means set only when lfb_depth > 8
also
0xa2 to 0x1df is not set

struct x86_linux_param_header {
        uint8_t  orig_x;                        /* 0x00 */  *
        uint8_t  orig_y;                        /* 0x01 */  *
        uint16_t ext_mem_k;                     /* 0x02 -- EXT_MEM_K sits here */   *
        uint16_t orig_video_page;               /* 0x04 */  *
        uint8_t  orig_video_mode;               /* 0x06 */  *
        uint8_t  orig_video_cols;               /* 0x07 */  *
        uint16_t unused2;                       /* 0x08 */
        uint16_t orig_video_ega_bx;             /* 0x0a */  *
        uint16_t unused3;                       /* 0x0c */
        uint8_t  orig_video_lines;              /* 0x0e */  *
        uint8_t  orig_video_isVGA;              /* 0x0f */   *
        uint16_t orig_video_points;             /* 0x10 */   *

        /* VESA graphic mode -- linear frame buffer */
        uint16_t lfb_width;                     /* 0x12 */   *
        uint16_t lfb_height;                    /* 0x14 */   *
        uint16_t lfb_depth;                     /* 0x16 */   *
        uint32_t lfb_base;                      /* 0x18 */   *
        uint32_t lfb_size;                      /* 0x1c */   *
        uint16_t cl_magic;                      /* 0x20 */   *
#define CL_MAGIC_VALUE 0xA33F
        uint16_t cl_offset;                     /* 0x22 */   *
        uint16_t lfb_linelength;                /* 0x24 */   *
        uint8_t  red_size;                      /* 0x26 */   ?
        uint8_t  red_pos;                       /* 0x27 */   ?
        uint8_t  green_size;                    /* 0x28 */   ?
        uint8_t  green_pos;                     /* 0x29 */   ?
        uint8_t  blue_size;                     /* 0x2a */   ?
        uint8_t  blue_pos;                      /* 0x2b */   ?
        uint8_t  rsvd_size;                     /* 0x2c */   ?
        uint8_t  rsvd_pos;                      /* 0x2d */   ?
        uint16_t vesapm_seg;                    /* 0x2e */   *
        uint16_t vesapm_off;                    /* 0x30 */
        uint16_t pages;                         /* 0x32 */   *
        uint8_t  reserved4[12];                 /* 0x34 -- 0x3f reserved for future expansion */

        struct apm_bios_info apm_bios_info;     /* 0x40 */   *
        struct drive_info_struct drive_info;    /* 0x80 */   *
        struct sys_desc_table sys_desc_table;   /* 0xa0 */   * only .length =
0, aka 0xa2 to 0x1df is not set
        uint32_t alt_mem_k;                     /* 0x1e0 */  *
        uint8_t  reserved5[4];                  /* 0x1e4 */
        uint8_t  e820_map_nr;                   /* 0x1e8 */  *
        uint8_t  eddbuf_entries;                /* 0x1e9 */  *
        uint8_t  edd_mbr_sig_buf_entries;       /* 0x1ea */  *
        uint8_t  reserved6[6];                  /* 0x1eb */
        HEADER.....                                         copied and or meset 0 and set.
        uint8_t  reserved16[0x290 - 0x248];     /* 0x248 */
        uint32_t edd_mbr_sig_buffer[EDD_MBR_SIG_MAX];   /* 0x290 */  *
#endif
        struct  e820entry e820_map[E820MAX];    /* 0x2d0 */   *
        uint8_t _pad8[48];                      /* 0xcd0 */
        struct  edd_info eddbuf[EDDMAXNR];      /* 0xd00 */   *
                                                /* 0xeec */

#define COMMAND_LINE_SIZE 2048
};

Quoted 2 lines

Also, does kexec set a bootloader ID?

no, 0xff

Quoted 67 lines · Yinghai Lu

Quoted 5 lines · H. Peter Anvin

Hi Eric,

Could you give a list of struct boot_params field which are initialized properly by kexec? I think we need to do the sentinel hack, and want to know what to whitelist.

the one with *
? means set only when lfb_depth > 8
also
0xa2 to 0x1df is not set

struct x86_linux_param_header {
        uint8_t  orig_x;                        /* 0x00 */  *
        uint8_t  orig_y;                        /* 0x01 */  *
        uint16_t ext_mem_k;                     /* 0x02 -- EXT_MEM_K sits here */   *
        uint16_t orig_video_page;               /* 0x04 */  *
        uint8_t  orig_video_mode;               /* 0x06 */  *
        uint8_t  orig_video_cols;               /* 0x07 */  *
        uint16_t unused2;                       /* 0x08 */
        uint16_t orig_video_ega_bx;             /* 0x0a */  *
        uint16_t unused3;                       /* 0x0c */
        uint8_t  orig_video_lines;              /* 0x0e */  *
        uint8_t  orig_video_isVGA;              /* 0x0f */   *
        uint16_t orig_video_points;             /* 0x10 */   *

        /* VESA graphic mode -- linear frame buffer */
        uint16_t lfb_width;                     /* 0x12 */   *
        uint16_t lfb_height;                    /* 0x14 */   *
        uint16_t lfb_depth;                     /* 0x16 */   *
        uint32_t lfb_base;                      /* 0x18 */   *
        uint32_t lfb_size;                      /* 0x1c */   *
        uint16_t cl_magic;                      /* 0x20 */   *
#define CL_MAGIC_VALUE 0xA33F
        uint16_t cl_offset;                     /* 0x22 */   *
        uint16_t lfb_linelength;                /* 0x24 */   *
        uint8_t  red_size;                      /* 0x26 */   ?
        uint8_t  red_pos;                       /* 0x27 */   ?
        uint8_t  green_size;                    /* 0x28 */   ?
        uint8_t  green_pos;                     /* 0x29 */   ?
        uint8_t  blue_size;                     /* 0x2a */   ?
        uint8_t  blue_pos;                      /* 0x2b */   ?
        uint8_t  rsvd_size;                     /* 0x2c */   ?
        uint8_t  rsvd_pos;                      /* 0x2d */   ?
        uint16_t vesapm_seg;                    /* 0x2e */   *
        uint16_t vesapm_off;                    /* 0x30 */
        uint16_t pages;                         /* 0x32 */   *
        uint8_t  reserved4[12];                 /* 0x34 -- 0x3f reserved for future expansion */

        struct apm_bios_info apm_bios_info;     /* 0x40 */   *
        struct drive_info_struct drive_info;    /* 0x80 */   *
        struct sys_desc_table sys_desc_table;   /* 0xa0 */   * only .length =
0, aka 0xa2 to 0x1df is not set
        uint32_t alt_mem_k;                     /* 0x1e0 */  *
        uint8_t  reserved5[4];                  /* 0x1e4 */
        uint8_t  e820_map_nr;                   /* 0x1e8 */  *
        uint8_t  eddbuf_entries;                /* 0x1e9 */  *
        uint8_t  edd_mbr_sig_buf_entries;       /* 0x1ea */  *
        uint8_t  reserved6[6];                  /* 0x1eb */
        HEADER.....                                         copied and or meset 0 and set.
        uint8_t  reserved16[0x290 - 0x248];     /* 0x248 */
        uint32_t edd_mbr_sig_buffer[EDD_MBR_SIG_MAX];   /* 0x290 */  *
#endif
        struct  e820entry e820_map[E820MAX];    /* 0x2d0 */   *
        uint8_t _pad8[48];                      /* 0xcd0 */
        struct  edd_info eddbuf[EDDMAXNR];      /* 0xd00 */   *
                                                /* 0xeec */

Quoted 8 lines

#define COMMAND_LINE_SIZE 2048
};

Quoted 2 lines

Also, does kexec set a bootloader ID?

no, 0xff

Hi, Peter,

What's your decision about this?

Do you mean have one boot_params mask in initdata and AND that with boot_params from bootloader
to clean not used bytes?

So later will not need to check
if (boot_params.hdr.xloadflags & USE_EXT_BOOT_PARAMS)
?

I worked out other patches that remove kdump 896M limitation. would like to post those patches to get more testing. those are needed for bigger system with lots of pcie devices.

Quoted 13 lines

Hi, Peter,

What's your decision about this?

Do you mean have one boot_params mask in initdata and AND that with boot_params from bootloader
to clean not used bytes?

So later will not need to check
if (boot_params.hdr.xloadflags & USE_EXT_BOOT_PARAMS)
?

Quoted 3 lines

I worked out other patches that remove kdump 896M limitation. would like to post those patches to get more testing. those are needed for bigger system with lots of pcie devices.

ping!

I still want to do what I mentioned before, because we need to not rely on the initialized/16-bit portion so much:

1. add a field in the uninitialized portion, call it "sentinel";
2. make sure the byte position corresponding to the "sentinel" field is nonzero in the bzImage file;
3. if the kernel boots up and sentinel is nonzero, erase those fields that you identified as uninitialized;

4. assign a proper boot loader ID to kexec, so we have a way of dealing with this kind of debacles in the future (that is what the bootloader ID is for: it gives us a way to work around bootloader-specific problems.)

We also need to formalize the 64-bit entry point properly, including all the entry conditions and so forth. That needs to be documented.