Re: [Qemu-devel] [PATCH 2/2] multiboot: Limit number of multiboot modules

[Kevin Wolf <kwolf@redhat.com>]

Am 14.10.2009 18:11, schrieb Adam Lackorzynski:
> Hi,
> 
> On Mon Oct 12, 2009 at 12:43:38 +0200, Kevin Wolf wrote:
>> Am 11.10.2009 15:48, schrieb adam@os.inf.tu-dresden.de:
>>> From: Adam Lackorzynski <adam@os.inf.tu-dresden.de>
>>>
>>> Add size checks to avoid overwriting the multiboot structure
>>> when too many modules are loaded.
>>>
>>> Signed-off-by: Adam Lackorzynski <adam@os.inf.tu-dresden.de>
>>
>> Acked-by: Kevin Wolf <kwolf@redhat.com>
>>
>> Looks correct, too, and is definitely an improvement over the current
>> code. But can't we make it more dynamic in a second step? I don't like
>> arbitrary fixed limits.
> 
> So, what do you think about the following? Removes any limit and loaded
> over hundred modules in my setup.
> 
> 
>  Subject: [PATCH 3/3] multiboot: Support arbitrary number of modules
> 
> Signed-off-by: Adam Lackorzynski <adam@os.inf.tu-dresden.de>

Looks good in general. I'm adding some minor comments inline.

> ---
>  hw/pc.c |  177 +++++++++++++++++++++++++++++++++++++++++----------------------
>  1 files changed, 116 insertions(+), 61 deletions(-)
> 
> diff --git a/hw/pc.c b/hw/pc.c
> index 21771c9..df01ab7 100644
> --- a/hw/pc.c
> +++ b/hw/pc.c
> @@ -588,6 +588,68 @@ static long get_file_size(FILE *f)
>  #error multiboot struct needs to fit in 16 bit real mode
>  #endif
>  
> +enum {
> +    /* Multiboot info */
> +    MBI_FLAGS       = 0,
> +    MBI_MEM_LOWER   = 4,
> +    MBI_MEM_UPPER   = 8,
> +    MBI_BOOT_DEVICE = 12,
> +    MBI_CMDLINE     = 16,
> +    MBI_MODS_COUNT  = 20,
> +    MBI_MODS_ADDR   = 24,
> +    MBI_MMAP_ADDR   = 48,
> +
> +    MBI_SIZE        = 88,
> +
> +    /* Multiboot modules */
> +    MB_MOD_START    = 0,
> +    MB_MOD_END      = 4,
> +    MB_MOD_CMDLINE  = 8,
> +
> +    MB_MOD_SIZE     = 16,
> +
> +    /* Region offsets */
> +    ADDR_E820_MAP = MULTIBOOT_STRUCT_ADDR + 0,
> +    ADDR_MBI      = ADDR_E820_MAP + 0x500,
> +};
> +
> +#define MULTIBOOT_FLAGS_MEMORY (1 << 0)
> +#define MULTIBOOT_FLAGS_BOOT_DEVICE (1 << 1)
> +#define MULTIBOOT_FLAGS_CMDLINE (1 << 2)
> +#define MULTIBOOT_FLAGS_MODULES (1 << 3)
> +#define MULTIBOOT_FLAGS_MMAP (1 << 6)

You could align the (1 << n) to the same column.

> +
> +static void *mb_buf;
> +static uint32_t mb_buf_phys; /* address in target */
> +static int mb_buf_size; /* size of mb_buf in bytes */
> +static int mb_mods_avail; /* available slots for mb_mods */
> +static int mb_mods_count;
> +static int mb_cmdlines_pos;

Maybe it's just me, but I don't like using global variables for this.
You could put them into a struct and pass it as a parameter to the
functions.

> +
> +static uint32_t mb_add_cmdline(const char *cmdline)
> +{
> +    int len = strlen(cmdline) + 1;
> +    uint32_t p = mb_cmdlines_pos;
> +
> +    assert(p + len <= mb_buf_size);
> +    pstrcpy((char *)mb_buf + p, len, cmdline);
> +    mb_cmdlines_pos += len;
> +    return mb_buf_phys + p;
> +}
> +
> +static void mb_add_mod(uint32_t start, uint32_t end,
> +                       uint32_t cmdline_phys)
> +{
> +    char *p;
> +    assert(mb_mods_count < mb_mods_avail);
> +
> +    p = (char *)mb_buf + MB_MOD_SIZE * mb_mods_count;
> +    stl_p(p + MB_MOD_START,   start);
> +    stl_p(p + MB_MOD_END,     end);
> +    stl_p(p + MB_MOD_CMDLINE, cmdline_phys);
> +    mb_mods_count++;
> +}
> +
>  static int load_multiboot(void *fw_cfg,
>                            FILE *f,
>                            const char *kernel_filename,
> @@ -600,11 +662,8 @@ static int load_multiboot(void *fw_cfg,
>      uint32_t mh_entry_addr;
>      uint32_t mh_load_addr;
>      uint32_t mb_kernel_size;
> -    uint32_t mmap_addr = MULTIBOOT_STRUCT_ADDR;
> -    uint32_t mb_bootinfo = MULTIBOOT_STRUCT_ADDR + 0x500;
> -    uint32_t mb_mod_end;
> -    uint8_t bootinfo[0x500];
> -    uint32_t cmdline = 0x200;
> +    uint32_t cur_end;
> +    uint8_t bootinfo[MBI_SIZE];
>  
>      /* Ok, let's see if it is a multiboot image.
>         The header is 12x32bit long, so the latest entry may be 8192 - 48. */
> @@ -687,90 +746,83 @@ static int load_multiboot(void *fw_cfg,
>          fclose(f);
>      }
>  
> -    /* blob size is only the kernel for now */
> -    mb_mod_end = mh_load_addr + mb_kernel_size;
> +    cur_end = TARGET_PAGE_ALIGN(mh_load_addr + mb_kernel_size);
> +
> +    /* Calculate space for cmdlines and mb_mods */
> +    mb_buf_size += strlen(kernel_filename) + 1;
> +    mb_buf_size += strlen(kernel_cmdline) + 1;
> +    if (initrd_filename) {
> +        const char *r = initrd_filename;
> +        mb_buf_size += strlen(r) + 1;
> +        mb_mods_avail = 1;
> +        while ((r = strchr(r, ','))) {
> +           mb_mods_avail++;
> +           r++;
> +        }
> +        mb_buf_size += MB_MOD_SIZE * mb_mods_avail;
> +    }
> +
> +    mb_buf      = qemu_mallocz(mb_buf_size);
> +    mb_buf_phys = cur_end;
> +
> +    mb_cmdlines_pos = mb_mods_avail * MB_MOD_SIZE;
> +
> +    cur_end += TARGET_PAGE_ALIGN(cur_end + mb_buf_size);

Sure that this isn't one cur_end too much if you're using += ?

>  
> -    /* load modules */
> -    stl_p(bootinfo + 20, 0x0); /* mods_count */
>      if (initrd_filename) {
> -        uint32_t mb_mod_info = 0x100;
> -        uint32_t mb_mod_cmdline = 0x300;
> -        uint32_t mb_mod_start = mh_load_addr;
> -        uint32_t mb_mod_length = mb_kernel_size;
>          char *next_initrd;
> -        char *next_space;
> -        int mb_mod_count = 0;
>  
>          do {
> -            if (mb_mod_info + 16 > mb_mod_cmdline) {
> -                printf("WARNING: Too many modules loaded, aborting.\n");
> -                break;
> -            }
> +            char *next_space;
> +            uint32_t mb_mod_length;
>              next_initrd = strchr(initrd_filename, ',');
>              if (next_initrd)
>                  *next_initrd = '\0';
>              /* if a space comes after the module filename, treat everything
>                 after that as parameters */
> -            pstrcpy((char*)bootinfo + mb_mod_cmdline,
> -                    sizeof(bootinfo) - mb_mod_cmdline,
> -                    initrd_filename);
> -            stl_p(bootinfo + mb_mod_info + 8, mb_bootinfo + mb_mod_cmdline); /* string */
> -            mb_mod_cmdline += strlen(initrd_filename) + 1;
> -            if (mb_mod_cmdline > sizeof(bootinfo)) {
> -                mb_mod_cmdline = sizeof(bootinfo);
> -                printf("WARNING: Too many module cmdlines loaded, aborting.\n");
> -                break;
> -            }
> +            uint32_t c = mb_add_cmdline(initrd_filename);
>              if ((next_space = strchr(initrd_filename, ' ')))
>                  *next_space = '\0';
>  #ifdef DEBUG_MULTIBOOT
>              printf("multiboot loading module: %s\n", initrd_filename);
>  #endif
> -            mb_mod_start = (mb_mod_start + mb_mod_length + (TARGET_PAGE_SIZE - 1))
> -                         & (TARGET_PAGE_MASK);
>              mb_mod_length = get_image_size(initrd_filename);
>              if (mb_mod_length < 0) {
>                  fprintf(stderr, "failed to get %s image size\n", initrd_filename);
>                  exit(1);
>              }
> -            mb_mod_end = mb_mod_start + mb_mod_length;
> -            rom_add_file_fixed(initrd_filename, mb_mod_start);
> +            rom_add_file_fixed(initrd_filename, cur_end);
>  
> -            mb_mod_count++;
> -            stl_p(bootinfo + mb_mod_info + 0, mb_mod_start);
> -            stl_p(bootinfo + mb_mod_info + 4, mb_mod_start + mb_mod_length);
> -            stl_p(bootinfo + mb_mod_info + 12, 0x0); /* reserved */
> +            mb_add_mod(cur_end, cur_end + mb_mod_length, c);
>  #ifdef DEBUG_MULTIBOOT
> -            printf("mod_start: %#x\nmod_end:   %#x\n", mb_mod_start,
> -                   mb_mod_start + mb_mod_length);
> +            printf("mod_start: %#x\nmod_end:   %#x\n", cur_end,
> +                   cur_end + mb_mod_length);
>  #endif
> +            cur_end = TARGET_PAGE_ALIGN(cur_end + mb_mod_length);
>              initrd_filename = next_initrd+1;
> -            mb_mod_info += 16;
>          } while (next_initrd);
> -        stl_p(bootinfo + 20, mb_mod_count); /* mods_count */
> -        stl_p(bootinfo + 24, mb_bootinfo + 0x100); /* mods_addr */
>      }
>  
>      /* Commandline support */
> -    stl_p(bootinfo + 16, mb_bootinfo + cmdline);
> -    snprintf((char*)bootinfo + cmdline, 0x100, "%s %s",
> +    char *kcmdline;
> +    asprintf(&kcmdline, "%s %s",
>               kernel_filename, kernel_cmdline);

Use snprintf instead of asprintf, the latter isn't available everywhere.

Kevin