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SubjectRE: [PATCH v3] tpm/tpm_crb: Avoid unaligned reads in crb_recv()
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> The current approach to read first 6 bytes from the response and then tail of
> the response, can cause the 2nd memcpy_fromio() to do an unaligned read
> (e.g. read 32-bit word from address aligned to a 16-bits), depending on how
> memcpy_fromio() is implemented. If this happens, the read will fail and the
> memory controller will fill the read with 1's.
>
> This was triggered by 170d13ca3a2f, which should be probably refined to check
> and react to the address alignment. Before that commit, on x86
> memcpy_fromio() turned out to be memcpy(). By a luck GCC has done the right
> thing (from tpm_crb's perspective) for us so far, but we should not rely on that.
> Thus, it makes sense to fix this also in tpm_crb, not least because the fix can be
> then backported to stable kernels and make them more robust when compiled
> in differing environments.
>
> Cc: stable@vger.kernel.org
> Cc: James Morris <jmorris@namei.org>
> Cc: Tomas Winkler <tomas.winkler@intel.com>
> Cc: Jerry Snitselaar <jsnitsel@redhat.com>
> Fixes: 30fc8d138e91 ("tpm: TPM 2.0 CRB Interface")
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
> ---
> v3:
> * Fix typo i.e. %s/reminding/remaining/g

Why you haven't fixed all the typos I've pointed out? I think you missed that.
Tomas

> v2:
> * There was a trailing double colon in the end of the short summary.
> * Check requested and expected length against TPM_HEADER_SIZE.
> * Add some explanatory comments to crb_recv().
> drivers/char/tpm/tpm_crb.c | 22 ++++++++++++++++------
> 1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c index
> 36952ef98f90..ee4df7815912 100644
> --- a/drivers/char/tpm/tpm_crb.c
> +++ b/drivers/char/tpm/tpm_crb.c
> @@ -287,19 +287,29 @@ static int crb_recv(struct tpm_chip *chip, u8 *buf,
> size_t count)
> struct crb_priv *priv = dev_get_drvdata(&chip->dev);
> unsigned int expected;
>
> - /* sanity check */
> - if (count < 6)
> + /* A sanity check that the upper layer wants to get at least the header
> + * as that is the minimum size for any TPM response.
> + */
> + if (count < TPM_HEADER_SIZE)
> return -EIO;
>
> + /* If this bit is set, according to the spec, the TPM is in unrecovable
> + * condition.
> + */
> if (ioread32(&priv->regs_t->ctrl_sts) & CRB_CTRL_STS_ERROR)
> return -EIO;
>
> - memcpy_fromio(buf, priv->rsp, 6);
> - expected = be32_to_cpup((__be32 *) &buf[2]);
> - if (expected > count || expected < 6)
> + /* Read 8 bytes (not just 6 bytes, which would cover the response
> length
> + * field) in order to make sure that the remaining memory accesses
> will
> + * be aligned.
> + */
> + memcpy_fromio(buf, priv->rsp, 8);
> +
> + expected = be32_to_cpup((__be32 *)&buf[2]);
> + if (expected > count || expected < TPM_HEADER_SIZE)
> return -EIO;
>
> - memcpy_fromio(&buf[6], &priv->rsp[6], expected - 6);
> + memcpy_fromio(&buf[8], &priv->rsp[8], expected - 8);
>
> return expected;
> }
> --
> 2.19.1

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