[Intel-gfx] [PATCH] drm/i915/bios: handle MIPI Sequence Block v3+ gracefully

[Jani Nikula]

The VBT MIPI Sequence Block version 3 has forward incompatible changes:

First, the block size in the header has been specified reserved, and the
actual size is a separate 32-bit value within the block. The current
find_section() function to will only look at the size in the block
header, and, depending on what's in that now reserved size field,
continue looking for other sections in the wrong place.

Fix this by taking the new block size field into account. This will
ensure that the lookups for other sections will work properly, as long
as the new 32-bit size does not go beyond the opregion VBT mailbox size.

Second, the contents of the block have been completely
changed. Gracefully refuse parsing the yet unknown data version.

Cc: Deepak M <m.deepak at intel.com>
Cc: stable at vger.kernel.org
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
---
 drivers/gpu/drm/i915/intel_bios.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
index c8acc2952f82..68421c273c8c 100644
--- a/drivers/gpu/drm/i915/intel_bios.c
+++ b/drivers/gpu/drm/i915/intel_bios.c
@@ -42,7 +42,7 @@ find_section(const void *_bdb, int section_id)
 	const struct bdb_header *bdb = _bdb;
 	const u8 *base = _bdb;
 	int index = 0;
-	u16 total, current_size;
+	u32 total, current_size;
 	u8 current_id;
 
 	/* skip to first section */
@@ -57,6 +57,10 @@ find_section(const void *_bdb, int section_id)
 		current_size = *((const u16 *)(base + index));
 		index += 2;
 
+		/* The MIPI Sequence Block v3+ has a separate size field. */
+		if (current_id == BDB_MIPI_SEQUENCE && *(base + index) >= 3)
+			current_size = *((const u32 *)(base + index + 1));
+
 		if (index + current_size > total)
 			return NULL;
 
@@ -799,6 +803,12 @@ parse_mipi(struct drm_i915_private *dev_priv, const struct bdb_header *bdb)
 		return;
 	}
 
+	/* Fail gracefully for forward incompatible sequence block. */
+	if (sequence->version >= 3) {
+		DRM_ERROR("Unable to parse MIPI Sequence Block v3+\n");
+		return;
+	}
+
 	DRM_DEBUG_DRIVER("Found MIPI sequence block\n");
 
 	block_size = get_blocksize(sequence);
-- 
2.1.4