linux-kernel - [PATCH 4.2 148/258] drm/i915/bios: handle MIPI Sequence Block v3+ gracefully

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Date:	Sat, 17 Oct 2015 18:57:41 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Deepak M <m.deepak@...el.com>,
	Jani Nikula <jani.nikula@...el.com>
Subject: [PATCH 4.2 148/258] drm/i915/bios: handle MIPI Sequence Block v3+ gracefully

4.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jani Nikula <jani.nikula@...el.com>

commit cd67d226ebd909d239d2c6e5a6abd6e2a338d1cd upstream.

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@...el.com>
Reviewed-by: Deepak M <m.deepak@...el.com>
Signed-off-by: Jani Nikula <jani.nikula@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/gpu/drm/i915/intel_bios.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- 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 secti
 	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 secti
 		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;
 
@@ -859,6 +863,12 @@ parse_mipi(struct drm_i915_private *dev_
 		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);


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