Re: [PATCH v2 1/4] tpm: fix signed/unsigned bug when checking event logs

[Ilias Apalodimas]

On Sat, 14 Sept 2024 at 02:20, Gregory Price <gourry@xxxxxxxxxx> wrote:
>
> A prior bugfix that fixes a signed/unsigned error causes
> another signed unsigned error.
>
> A situation where log_tbl->size is invalid can cause the
> size passed to memblock_reserve to become negative.
>
> log_size from the main event log is an unsigned int, and
> the code reduces to the following
>
> u64 value = (int)unsigned_value;
>
> This results in sign extension, and the value sent to
> memblock_reserve becomes effectively negative.
>
> Fixes: be59d57f9806 ("efi/tpm: Fix sanity check of unsigned tbl_size being less than zero")
> Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>
> ---
>  drivers/firmware/efi/tpm.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/firmware/efi/tpm.c b/drivers/firmware/efi/tpm.c
> index e8d69bd548f3..9c3613e6af15 100644
> --- a/drivers/firmware/efi/tpm.c
> +++ b/drivers/firmware/efi/tpm.c
> @@ -40,7 +40,8 @@ int __init efi_tpm_eventlog_init(void)
>  {
>         struct linux_efi_tpm_eventlog *log_tbl;
>         struct efi_tcg2_final_events_table *final_tbl;
> -       int tbl_size;
> +       unsigned int tbl_size;

nit, perhaps u32 is better here

> +       int final_tbl_size;
>         int ret = 0;
>
>         if (efi.tpm_log == EFI_INVALID_TABLE_ADDR) {
> @@ -80,26 +81,26 @@ int __init efi_tpm_eventlog_init(void)
>                 goto out;
>         }
>
> -       tbl_size = 0;
> +       final_tbl_size = 0;
>         if (final_tbl->nr_events != 0) {
>                 void *events = (void *)efi.tpm_final_log
>                                 + sizeof(final_tbl->version)
>                                 + sizeof(final_tbl->nr_events);
>
> -               tbl_size = tpm2_calc_event_log_size(events,
> -                                                   final_tbl->nr_events,
> -                                                   log_tbl->log);
> +               final_tbl_size = tpm2_calc_event_log_size(events,
> +                                                         final_tbl->nr_events,
> +                                                         log_tbl->log);
>         }
>
> -       if (tbl_size < 0) {
> +       if (final_tbl_size < 0) {
>                 pr_err(FW_BUG "Failed to parse event in TPM Final Events Log\n");
>                 ret = -EINVAL;
>                 goto out_calc;
>         }
>
>         memblock_reserve(efi.tpm_final_log,
> -                        tbl_size + sizeof(*final_tbl));
> -       efi_tpm_final_log_size = tbl_size;
> +                        final_tbl_size + sizeof(*final_tbl));
> +       efi_tpm_final_log_size = final_tbl_size;
>
>  out_calc:
>         early_memunmap(final_tbl, sizeof(*final_tbl));
> --
> 2.43.0
>

Reviewed-by: Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx>