Re: [Qemu-devel] [PATCH] bios-linker-loader: document+validate input

[Igor Mammedov]

On Sun, 21 Feb 2016 15:03:04 +0200
"Michael S. Tsirkin" <address@hidden> wrote:

> While guest/host ABI is documented in hw/acpi/bios-linker-loader.c,
> the API was left undocumented.
> 
> This adds documentation for all API functions.
> 
> Additionally, input is validated to make sure all
> pointers fall within range of provided files.
> 
> To allow this validation for checksum commands,
> bios_linker_loader_add_checksum is changed to accept GArray * in place
> of void *.
> 
> Reported-by: Igor Mammedov <address@hidden>
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
> 
> Igor, I hope this validation addresses most of your comments,
> and makes the API clear.
> 
> You had ideas to add a wrapper for bios_linker_loader_add_pointer
> that pushes and initializes the pointer automatically.
> If you still think it's a good idea, it should now be easy
> for you to implement this wrapper yourself.
> 
> 
>  include/hw/acpi/bios-linker-loader.h |  2 +-
>  hw/acpi/aml-build.c                  |  2 +-
>  hw/acpi/bios-linker-loader.c         | 91 
> ++++++++++++++++++++++++++++++++++--
>  hw/arm/virt-acpi-build.c             |  3 +-
>  hw/i386/acpi-build.c                 |  3 +-
>  5 files changed, 92 insertions(+), 9 deletions(-)
> 
> diff --git a/include/hw/acpi/bios-linker-loader.h 
> b/include/hw/acpi/bios-linker-loader.h
> index 498c0af..e54b6b4 100644
> --- a/include/hw/acpi/bios-linker-loader.h
> +++ b/include/hw/acpi/bios-linker-loader.h
> @@ -13,7 +13,7 @@ void bios_linker_loader_alloc(GArray *linker,
>                                bool alloc_fseg);
>  
>  void bios_linker_loader_add_checksum(GArray *linker, const char *file,
> -                                     void *table,
> +                                     GArray *table,
>                                       void *start, unsigned size,
>                                       uint8_t *checksum);
>  
> diff --git a/hw/acpi/aml-build.c b/hw/acpi/aml-build.c
> index 603068b..6675535 100644
> --- a/hw/acpi/aml-build.c
> +++ b/hw/acpi/aml-build.c
> @@ -1451,7 +1451,7 @@ build_header(GArray *linker, GArray *table_data,
>      h->checksum = 0;
>      /* Checksum to be filled in by Guest linker */
>      bios_linker_loader_add_checksum(linker, ACPI_BUILD_TABLE_FILE,
> -                                    table_data->data, h, len, &h->checksum);
> +                                    table_data, h, len, &h->checksum);
>  }
>  
>  void *acpi_data_push(GArray *table_data, unsigned size)
> diff --git a/hw/acpi/bios-linker-loader.c b/hw/acpi/bios-linker-loader.c
> index e04d60a..ace9abb 100644
> --- a/hw/acpi/bios-linker-loader.c
> +++ b/hw/acpi/bios-linker-loader.c
> @@ -25,6 +25,13 @@
>  
>  #include "qemu/bswap.h"
>  
> +/*
> + * Linker/loader is a paravirtualized interface that passes commands to 
> guest.
> + * The commands can be used to request guest to
> + * - allocate memory chunks and initialize them from QEMU FW CFG files
> + * - link allocated chunks by storing pointer to one chunk into another
> + * - calculate ACPI checksum of part of the chunk and store into same chunk
> + */
>  #define BIOS_LINKER_LOADER_FILESZ FW_CFG_MAX_FILE_PATH
>  
>  struct BiosLinkerLoaderEntry {
> @@ -88,6 +95,12 @@ enum {
>      BIOS_LINKER_LOADER_ALLOC_ZONE_FSEG = 0x2,
>  };
>  
> +/*
> + * bios_linker_loader_init: allocate a new linker file blob array.
> + *
> + * After initialization, linker commands can be added, and will
> + * be stored in the array.
> + */
>  GArray *bios_linker_loader_init(void)
>  {
>      return g_array_new(false, true /* clear */, 1);
> @@ -99,6 +112,16 @@ void *bios_linker_loader_cleanup(GArray *linker)
>      return g_array_free(linker, false);
>  }
>  
> +/*
> + * bios_linker_loader_alloc: ask guest to load file into guest memory.
> + *
> + * @linker: linker file blob array
> + * @file: file to be loaded
> + * @alloc_align: required minimal alignment in bytes. Must be a power of 2.
> + * @alloc_fseg: request allocation in FSEG zone (useful for the RSDP ACPI 
> table)
> + *
> + * Note: this command must precede any other linker command using this file.
> + */
>  void bios_linker_loader_alloc(GArray *linker,
>                                const char *file,
>                                uint32_t alloc_align,
> @@ -106,6 +129,8 @@ void bios_linker_loader_alloc(GArray *linker,
>  {
>      BiosLinkerLoaderEntry entry;
>  
> +    assert(!(alloc_align & (alloc_align - 1)));
> +
>      memset(&entry, 0, sizeof entry);
>      strncpy(entry.alloc.file, file, sizeof entry.alloc.file - 1);
>      entry.command = cpu_to_le32(BIOS_LINKER_LOADER_COMMAND_ALLOCATE);
> @@ -118,23 +143,77 @@ void bios_linker_loader_alloc(GArray *linker,
>      g_array_prepend_vals(linker, &entry, sizeof entry);
>  }
>  
> +/*
> + * bios_linker_loader_add_checksum: ask guest to add checksum of file data
> + * into (same) file at the specified pointer.
> + *
> + * Checksum calculation simply sums -X for each byte X in the range
> + * using 8-bit math (i.e. ACPI checksum).
> + *
> + * @linker: linker file blob array
> + * @file: file that includes the checksum to be calculated
> + *        and the data to be checksummed
> + * @table: @file blob contents
> + * @start, @size: range of data to checksum
> + * @checksum: location of the checksum to be patched within file blob
> + *
> + * Notes:
> + * - checksum byte initial value must have been pushed into @table
> + *   and reside at address @checksum.
> + * - @size bytes must have been pushed into @table and reside at address
> + *   @start.
> + * - Guest calculates checksum of specified range of data, result is added to
> + *   initial value at @checksum into copy of @file in Guest memory.
> + * - Range might include the checksum itself.
> + * - To avoid confusion, caller must always put 0x0 at @checksum.
> + * - @file must be loaded into Guest memory using bios_linker_loader_alloc
> + */
>  void bios_linker_loader_add_checksum(GArray *linker, const char *file,
> -                                     void *table,
> +                                     GArray *table,
>                                       void *start, unsigned size,
>                                       uint8_t *checksum)
>  {
>      BiosLinkerLoaderEntry entry;
> +    ptrdiff_t checksum_offset = (gchar *)checksum - table->data;
> +    ptrdiff_t start_offset = (gchar *)start - table->data;
> +
> +    assert(checksum_offset >= 0);
> +    assert(start_offset >= 0);
> +    assert(checksum_offset + 1 <= table->len);
> +    assert(start_offset + size <= table->len);
> +    assert(*checksum == 0x0);
>  
>      memset(&entry, 0, sizeof entry);
>      strncpy(entry.cksum.file, file, sizeof entry.cksum.file - 1);
>      entry.command = cpu_to_le32(BIOS_LINKER_LOADER_COMMAND_ADD_CHECKSUM);
> -    entry.cksum.offset = cpu_to_le32(checksum - (uint8_t *)table);
> -    entry.cksum.start = cpu_to_le32((uint8_t *)start - (uint8_t *)table);
> +    entry.cksum.offset = cpu_to_le32(checksum_offset);
> +    entry.cksum.start = cpu_to_le32(start_offset);
>      entry.cksum.length = cpu_to_le32(size);
>  
>      g_array_append_vals(linker, &entry, sizeof entry);
>  }
>  
> +/*
> + * bios_linker_loader_add_pointer: ask guest to add address of source file
> + * into destination file at the specified pointer.
> + *
> + * @linker: linker file blob array
> + * @dest_file: destination file that must be changed
> + * @src_file: source file who's address must be taken
> + * @table: @dest_file blob contents array
> + * @pointer: location of the pointer to be patched within destination file 
> blob
> + * @pointer_size: size of pointer to be patched, in bytes
> + *
> + * Notes:
> + * - @pointer_size bytes must have been pushed into @table
> + *   and reside at address @pointer.
> + * - Guest address is added to initial value at @pointer
> + *   into copy of @dest_file in Guest memory.
> + *   e.g. to get start of src_file in guest memory, put 0x0 there
> + *   to get address of a field at offset 0x10 in src_file, put 0x10 there

I'd rather API use explicit offsets as arguments instead of
doing above.

 + * @linker: linker file blob array
 + * @dest_file: destination file that must be changed
 + * @src_file: source file who's address must be taken
 + * @src_offset: location within source file to which @address@hidden will 
point to after ADD_POINTER command is executed
 + * @dst_patched_offset: location within destination file blob to be patched 
with a pointer to @src_file allocated blob in Guest memory + @src_offset
 + * @dst_patched_offset: size of pointer to be patched, in bytes

> + * - Both @dest_file and @src_file must be
> + *   loaded into Guest memory using bios_linker_loader_alloc
> + */
>  void bios_linker_loader_add_pointer(GArray *linker,
>                                      const char *dest_file,
>                                      const char *src_file,
> @@ -142,7 +221,10 @@ void bios_linker_loader_add_pointer(GArray *linker,
>                                      uint8_t pointer_size)
>  {
>      BiosLinkerLoaderEntry entry;
> -    size_t offset = (gchar *)pointer - table->data;
> +    ptrdiff_t offset = (gchar *)pointer - table->data;
> +
> +    assert(offset >= 0);
> +    assert(offset + pointer_size <= table->len);
>  
>      memset(&entry, 0, sizeof entry);
>      strncpy(entry.pointer.dest_file, dest_file,
> @@ -150,7 +232,6 @@ void bios_linker_loader_add_pointer(GArray *linker,
>      strncpy(entry.pointer.src_file, src_file,
>              sizeof entry.pointer.src_file - 1);
>      entry.command = cpu_to_le32(BIOS_LINKER_LOADER_COMMAND_ADD_POINTER);
> -    assert(table->len >= offset + pointer_size);
>      entry.pointer.offset = cpu_to_le32(offset);
>      entry.pointer.size = pointer_size;
>      assert(pointer_size == 1 || pointer_size == 2 ||
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index 9876932..c076bbf 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -359,7 +359,8 @@ build_rsdp(GArray *rsdp_table, GArray *linker, unsigned 
> rsdt)
>      rsdp->checksum = 0;
>      /* Checksum to be filled by Guest linker */
>      bios_linker_loader_add_checksum(linker, ACPI_BUILD_RSDP_FILE,
> -                                    rsdp, rsdp, sizeof *rsdp, 
> &rsdp->checksum);
> +                                    rsdp_table, rsdp, sizeof *rsdp,
> +                                    &rsdp->checksum);
>  
>      return rsdp_table;
>  }
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index 36752b2..b654b0d 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -2532,7 +2532,8 @@ build_rsdp(GArray *rsdp_table, GArray *linker, unsigned 
> rsdt)
>      rsdp->checksum = 0;
>      /* Checksum to be filled by Guest linker */
>      bios_linker_loader_add_checksum(linker, ACPI_BUILD_RSDP_FILE,
> -                                    rsdp, rsdp, sizeof *rsdp, 
> &rsdp->checksum);
> +                                    rsdp_table, rsdp, sizeof *rsdp,
> +                                    &rsdp->checksum);
>  
>      return rsdp_table;
>  }