Re: [PATCH 09/10] drm/i915/dmc: protect against reading random memory

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Thu, May 23, 2019 at 01:24:19AM -0700, Lucas De Marchi wrote:
> While loading the DMC firmware we were double checking the headers made
> sense, but in no place we checked that we were actually reading memory
> we were supposed to. This could be wrong in case the firmware file is
> truncated.
> 
> Before parsing any part of the firmware, validate the input first.
> 
> Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>

I wonder if this patch should be the first one on the series
for easy backport if needed.
Maybe cc: Stable?

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

> ---
>  drivers/gpu/drm/i915/intel_csr.c | 71 ++++++++++++++++++++++++--------
>  1 file changed, 53 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_csr.c b/drivers/gpu/drm/i915/intel_csr.c
> index 7ff08de83cc6..b7181ca6c8f5 100644
> --- a/drivers/gpu/drm/i915/intel_csr.c
> +++ b/drivers/gpu/drm/i915/intel_csr.c
> @@ -360,7 +360,8 @@ static u32 find_dmc_fw_offset(const struct intel_fw_info *fw_info,
>  }
>  
>  static u32 parse_csr_fw_dmc(struct intel_csr *csr,
> -			    const struct intel_dmc_header_base *dmc_header)
> +			    const struct intel_dmc_header_base *dmc_header,
> +			    size_t rem_size)
>  {
>  	unsigned int header_len_bytes, dmc_header_size, payload_size, i;
>  	const u32 *mmioaddr, *mmiodata;
> @@ -375,6 +376,9 @@ static u32 parse_csr_fw_dmc(struct intel_csr *csr,
>  		const struct intel_dmc_header_v3 *v3 =
>  			(const struct intel_dmc_header_v3 *)dmc_header;
>  
> +		if (rem_size < sizeof(struct intel_dmc_header_v3))
> +			goto error_truncated;
> +
>  		mmioaddr = v3->mmioaddr;
>  		mmiodata = v3->mmiodata;
>  		mmio_count = v3->mmio_count;
> @@ -386,6 +390,9 @@ static u32 parse_csr_fw_dmc(struct intel_csr *csr,
>  		const struct intel_dmc_header_v1 *v1 =
>  			(const struct intel_dmc_header_v1 *)dmc_header;
>  
> +		if (rem_size < sizeof(struct intel_dmc_header_v1))
> +			goto error_truncated;
> +
>  		mmioaddr = v1->mmioaddr;
>  		mmiodata = v1->mmiodata;
>  		mmio_count = v1->mmio_count;
> @@ -404,6 +411,8 @@ static u32 parse_csr_fw_dmc(struct intel_csr *csr,
>  		return 0;
>  	}
>  
> +	rem_size -= header_len_bytes;
> +
>  	/* Cache the dmc header info. */
>  	if (mmio_count > mmio_count_max) {
>  		DRM_ERROR("DMC firmware has wrong mmio count %u\n", mmio_count);
> @@ -424,6 +433,9 @@ static u32 parse_csr_fw_dmc(struct intel_csr *csr,
>  
>  	/* fw_size is in dwords, so multiplied by 4 to convert into bytes. */
>  	payload_size = dmc_header->fw_size * 4;
> +	if (rem_size < payload_size)
> +		goto error_truncated;
> +
>  	if (payload_size > csr->max_fw_size) {
>  		DRM_ERROR("DMC FW too big (%u bytes)\n", payload_size);
>  		return 0;
> @@ -440,16 +452,25 @@ static u32 parse_csr_fw_dmc(struct intel_csr *csr,
>  	memcpy(csr->dmc_payload, payload, payload_size);
>  
>  	return header_len_bytes + payload_size;
> +
> +error_truncated:
> +	DRM_ERROR("Truncated DMC firmware, refusing.\n");
> +	return 0;
>  }
>  
>  static u32
>  parse_csr_fw_package(struct intel_csr *csr,
>  		     const struct intel_package_header *package_header,
> -		     const struct stepping_info *si)
> +		     const struct stepping_info *si,
> +		     size_t rem_size)
>  {
> -	u32 num_entries, max_entries, dmc_offset, r;
> +	u32 package_size = sizeof(struct intel_package_header);
> +	u32 num_entries, max_entries, dmc_offset;
>  	const struct intel_fw_info *fw_info;
>  
> +	if (rem_size < package_size)
> +		goto error_truncated;
> +
>  	if (package_header->header_ver == 1) {
>  		max_entries = PACKAGE_MAX_FW_INFO_ENTRIES;
>  	} else if (package_header->header_ver == 2) {
> @@ -460,11 +481,17 @@ parse_csr_fw_package(struct intel_csr *csr,
>  		return 0;
>  	}
>  
> -	if (package_header->header_len * 4 !=
> -	    sizeof(struct intel_package_header) +
> -	    max_entries * sizeof(struct intel_fw_info)) {
> +	/*
> +	 * We should always have space for max_entries,
> +	 * even if not all are used
> +	 */
> +	package_size += max_entries * sizeof(struct intel_fw_info);
> +	if (rem_size < package_size)
> +		goto error_truncated;
> +
> +	if (package_header->header_len * 4 != package_size) {
>  		DRM_ERROR("DMC firmware has wrong package header length "
> -			  "(%u bytes)\n", package_header->header_len * 4);
> +			  "(%u bytes)\n", package_size);
>  		return 0;
>  	}
>  
> @@ -481,21 +508,24 @@ parse_csr_fw_package(struct intel_csr *csr,
>  		return 0;
>  	}
>  
> -	r = sizeof(struct intel_package_header);
> -
> -	/* we always have space for max_entries, even if not all are used */
> -	r += max_entries * sizeof(struct intel_fw_info);
> -
>  	/* dmc_offset is in dwords */
> -	r += dmc_offset * 4;
> +	return package_size + dmc_offset * 4;
>  
> -	return r;
> +error_truncated:
> +	DRM_ERROR("Truncated DMC firmware, refusing.\n");
> +	return 0;
>  }
>  
>  /* Return number of bytes parsed or 0 on error */
>  static u32 parse_csr_fw_css(struct intel_csr *csr,
> -			    struct intel_css_header *css_header)
> +			    struct intel_css_header *css_header,
> +			    size_t rem_size)
>  {
> +	if (rem_size < sizeof(struct intel_css_header)) {
> +		DRM_ERROR("Truncated DMC firmware, refusing.\n");
> +		return 0;
> +	}
> +
>  	if (sizeof(struct intel_css_header) !=
>  	    (css_header->header_len * 4)) {
>  		DRM_ERROR("DMC firmware has wrong CSS header length "
> @@ -530,29 +560,34 @@ static void parse_csr_fw(struct drm_i915_private *dev_priv,
>  	const struct stepping_info *si = intel_get_stepping_info(dev_priv);
>  	u32 readcount = 0;
>  	u32 r;
> +	size_t rem_size;
>  
>  	if (!fw)
>  		return;
>  
> +	rem_size = fw->size;
> +
>  	/* Extract CSS Header information*/
>  	css_header = (struct intel_css_header *)fw->data;
> -	r = parse_csr_fw_css(csr, css_header);
> +	r = parse_csr_fw_css(csr, css_header, rem_size);
>  	if (!r)
>  		return;
>  
> +	rem_size -= r;
>  	readcount += r;
>  
>  	/* Extract Package Header information*/
>  	package_header = (struct intel_package_header *)&fw->data[readcount];
> -	r = parse_csr_fw_package(csr, package_header, si);
> +	r = parse_csr_fw_package(csr, package_header, si, rem_size);
>  	if (!r)
>  		return;
>  
> +	rem_size -= r;
>  	readcount += r;
>  
>  	/* Extract dmc_header information. */
>  	dmc_header = (struct intel_dmc_header_base *)&fw->data[readcount];
> -	parse_csr_fw_dmc(csr, dmc_header);
> +	parse_csr_fw_dmc(csr, dmc_header, rem_size);
>  }
>  
>  static void intel_csr_runtime_pm_get(struct drm_i915_private *dev_priv)
> -- 
> 2.21.0
> 
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