[SLOF] [PATCH 2/2] tcgbios: Only measure size indicated in UEFI partition table header

[Alexey Kardashevskiy]

On Tue, 25 Mar 2025, at 04:29, Stefan Berger wrote:
> From: Stefan Berger <stefanb at linux.ibm.com>
> 
> Remove the reserved byte array from the UEFI_PARTITION_TABLE_HEADER
> to avoid measuring zero bytes. Only log and measure the header as
> indicated by its size. This size is expected to be exactly the size
> of UEFI_PARTITION_TABLE_HEADER (= 92 bytes).
> 
> Fixes: 16a1867425ee ("tcgbios: Measure the GPT table")
> Signed-off-by: Stefan Berger <stefanb at linux.ibm.com>
> ---
> lib/libtpm/tcgbios.c     | 19 +++++++++++++++++--
> lib/libtpm/tcgbios_int.h |  1 -
> 2 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/libtpm/tcgbios.c b/lib/libtpm/tcgbios.c
> index 9a10dbe..8fd404e 100644
> --- a/lib/libtpm/tcgbios.c
> +++ b/lib/libtpm/tcgbios.c
> @@ -1080,6 +1080,9 @@ uint32_t tpm_measure_bcv_mbr(uint32_t bootdrv, const uint8_t *addr,
>   */
> void tpm_gpt_set_lba1(const uint8_t *addr, uint32_t length)
> {
> + UEFI_PARTITION_TABLE_HEADER *upth;

You could initialize it right here.

> + size_t to_copy;
> +
> if (!tpm_is_working())
> return;
>  
> @@ -1090,8 +1093,20 @@ void tpm_gpt_set_lba1(const uint8_t *addr, uint32_t length)
> if (!uefi_gpt_data)
> return;
>  
> - memcpy(&uefi_gpt_data->EfiPartitionHeader,
> -        addr, MIN(sizeof(uefi_gpt_data->EfiPartitionHeader), length));
> + upth = (UEFI_PARTITION_TABLE_HEADER *)addr;
> +
> + /* check whether header.size is part of @addr array */
> + if (length < offset_of(UEFI_PARTITION_TABLE_HEADER, header.size) +
> + sizeof(upth->header.size))

It should really be "length < sizeof(uefi_gpt_data->EfiPartitionHeader)" here and drop "length < to_copy" below.

> + return;
> + to_copy = le32_to_cpu(upth->header.size);
> +
> + /* Expecting to copy exactly the size of EfiPartitionHeader (92bytes) */
> + if (length < to_copy ||
> +     to_copy != sizeof(uefi_gpt_data->EfiPartitionHeader))

if ( le32_to_cpu(upth->header.size) != sizeof(uefi_gpt_data->EfiPartitionHeader))
   return;

> + return;
> +
> + memcpy(&uefi_gpt_data->EfiPartitionHeader, addr, to_copy);

s/to_copy/sizeof(uefi_gpt_data->EfiPartitionHeader)/

and then you can ditch @to_copy. Thanks,

> uefi_gpt_data->NumberOfPartitions = cpu_to_le64(0);
> }
>  
> diff --git a/lib/libtpm/tcgbios_int.h b/lib/libtpm/tcgbios_int.h
> index cc38455..5bbd9d5 100644
> --- a/lib/libtpm/tcgbios_int.h
> +++ b/lib/libtpm/tcgbios_int.h
> @@ -116,7 +116,6 @@ typedef struct {
> uint32_t numPartEntry;
> uint32_t partEntrySize;
> uint32_t partArrayCrc32;
> - uint8_t reserved[420];
> } __attribute__((packed)) UEFI_PARTITION_TABLE_HEADER;
>  
> typedef struct {
> -- 
> 2.25.1
> 
>