Re: [Intel-gfx] [PATCH 1/2] drm/i915/bios: Validate fp_timing terminator presence

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Sep 02, 2022 at 01:47:14PM +0300, Jani Nikula wrote:
> On Thu, 18 Aug 2022, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > Validate the LFP data block a bit hardwer by making sure the
> > fp_timing terminators (0xffff) are where we expect them to be.
> >
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> I wonder if it would be good to debug log at each of the "return false"
> sites in fixup_lfp_data_ptrs() and validate_lfp_data_ptrs(). Anyway,
> that's a separate change.

Not sure how much it would help. I suspect one still ends
up decoding the whole hexdump by hand.

> 
> Reviewed-by: Jani Nikula <jani.nikula@intel.com>
> 
> > ---
> >  drivers/gpu/drm/i915/display/intel_bios.c | 60 ++++++++++++-----------
> >  1 file changed, 32 insertions(+), 28 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> > index 198a2f4920cc..f1f861da9e93 100644
> > --- a/drivers/gpu/drm/i915/display/intel_bios.c
> > +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> > @@ -135,18 +135,6 @@ static u32 raw_block_offset(const void *bdb, enum bdb_block_id section_id)
> >  	return block - bdb;
> >  }
> >  
> > -/* size of the block excluding the header */
> > -static u32 raw_block_size(const void *bdb, enum bdb_block_id section_id)
> > -{
> > -	const void *block;
> > -
> > -	block = find_raw_section(bdb, section_id);
> > -	if (!block)
> > -		return 0;
> > -
> > -	return get_blocksize(block);
> > -}
> > -
> >  struct bdb_block_entry {
> >  	struct list_head node;
> >  	enum bdb_block_id section_id;
> > @@ -231,9 +219,14 @@ static bool validate_lfp_data_ptrs(const void *bdb,
> >  {
> >  	int fp_timing_size, dvo_timing_size, panel_pnp_id_size, panel_name_size;
> >  	int data_block_size, lfp_data_size;
> > +	const void *data_block;
> >  	int i;
> >  
> > -	data_block_size = raw_block_size(bdb, BDB_LVDS_LFP_DATA);
> > +	data_block = find_raw_section(bdb, BDB_LVDS_LFP_DATA);
> > +	if (!data_block)
> > +		return false;
> > +
> > +	data_block_size = get_blocksize(data_block);
> >  	if (data_block_size == 0)
> >  		return false;
> >  
> > @@ -261,21 +254,6 @@ static bool validate_lfp_data_ptrs(const void *bdb,
> >  	if (16 * lfp_data_size > data_block_size)
> >  		return false;
> >  
> > -	/*
> > -	 * Except for vlv/chv machines all real VBTs seem to have 6
> > -	 * unaccounted bytes in the fp_timing table. And it doesn't
> > -	 * appear to be a really intentional hole as the fp_timing
> > -	 * 0xffff terminator is always within those 6 missing bytes.
> > -	 */
> > -	if (fp_timing_size + dvo_timing_size + panel_pnp_id_size != lfp_data_size &&
> > -	    fp_timing_size + 6 + dvo_timing_size + panel_pnp_id_size != lfp_data_size)
> > -		return false;
> > -
> > -	if (ptrs->ptr[0].fp_timing.offset + fp_timing_size > ptrs->ptr[0].dvo_timing.offset ||
> > -	    ptrs->ptr[0].dvo_timing.offset + dvo_timing_size != ptrs->ptr[0].panel_pnp_id.offset ||
> > -	    ptrs->ptr[0].panel_pnp_id.offset + panel_pnp_id_size != lfp_data_size)
> > -		return false;
> > -
> >  	/* make sure the table entries have uniform size */
> >  	for (i = 1; i < 16; i++) {
> >  		if (ptrs->ptr[i].fp_timing.table_size != fp_timing_size ||
> > @@ -289,6 +267,23 @@ static bool validate_lfp_data_ptrs(const void *bdb,
> >  			return false;
> >  	}
> >  
> > +	/*
> > +	 * Except for vlv/chv machines all real VBTs seem to have 6
> > +	 * unaccounted bytes in the fp_timing table. And it doesn't
> > +	 * appear to be a really intentional hole as the fp_timing
> > +	 * 0xffff terminator is always within those 6 missing bytes.
> > +	 */
> > +	if (fp_timing_size + 6 + dvo_timing_size + panel_pnp_id_size == lfp_data_size)
> > +		fp_timing_size += 6;
> > +
> > +	if (fp_timing_size + dvo_timing_size + panel_pnp_id_size != lfp_data_size)
> > +		return false;
> > +
> > +	if (ptrs->ptr[0].fp_timing.offset + fp_timing_size != ptrs->ptr[0].dvo_timing.offset ||
> > +	    ptrs->ptr[0].dvo_timing.offset + dvo_timing_size != ptrs->ptr[0].panel_pnp_id.offset ||
> > +	    ptrs->ptr[0].panel_pnp_id.offset + panel_pnp_id_size != lfp_data_size)
> > +		return false;
> > +
> >  	/* make sure the tables fit inside the data block */
> >  	for (i = 0; i < 16; i++) {
> >  		if (ptrs->ptr[i].fp_timing.offset + fp_timing_size > data_block_size ||
> > @@ -300,6 +295,15 @@ static bool validate_lfp_data_ptrs(const void *bdb,
> >  	if (ptrs->panel_name.offset + 16 * panel_name_size > data_block_size)
> >  		return false;
> >  
> > +	/* make sure fp_timing terminators are present at expected locations */
> > +	for (i = 0; i < 16; i++) {
> > +		const u16 *t = data_block + ptrs->ptr[i].fp_timing.offset +
> > +			fp_timing_size - 2;
> > +
> > +		if (*t != 0xffff)
> > +			return false;
> > +	}
> > +
> >  	return true;
> >  }
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center

-- 
Ville Syrjälä
Intel