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@@ -0,0 +1,65 @@
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+From: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= <[email protected]>
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+Subject: [PATCH] mtd: bcm47xxpart: improve handling TRX partition size
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+MIME-Version: 1.0
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+Content-Type: text/plain; charset=UTF-8
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+Content-Transfer-Encoding: 8bit
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+
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+When bcm47xxpart finds a TRX partition (container) it's supposed to jump
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+to the end of it and keep looking for more partitions. TRX and its
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+subpartitions are handled be a separated parser.
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+
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+The problem with old code was relying on the length specified in a TRX
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+header. That isn't reliable as TRX is commonly modified to have checksum
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+cover only non-changing subpartitions. Otherwise modifying e.g. a rootfs
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+would result in CRC32 mismatch and bootloader refusing to boot a
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+firmware.
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+
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+Fix it by trying better to figure out a real TRX size. We can securely
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+assume that TRX has to cover all subpartitions and the last one is at
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+least of a block size in size. Then compare it with a length field.
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+
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+This makes code more optimal & reliable thanks to skipping data that
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+shouldn't be parsed.
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+
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+Signed-off-by: Rafał Miłecki <[email protected]>
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+---
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+
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+--- a/drivers/mtd/bcm47xxpart.c
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++++ b/drivers/mtd/bcm47xxpart.c
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+@@ -186,6 +186,8 @@ static int bcm47xxpart_parse(struct mtd_
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+ /* TRX */
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+ if (buf[0x000 / 4] == TRX_MAGIC) {
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+ struct trx_header *trx;
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++ uint32_t last_subpart;
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++ uint32_t trx_size;
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+
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+ if (trx_num >= ARRAY_SIZE(trx_parts))
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+ pr_warn("No enough space to store another TRX found at 0x%X\n",
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+@@ -195,11 +197,23 @@ static int bcm47xxpart_parse(struct mtd_
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+ bcm47xxpart_add_part(&parts[curr_part++], "firmware",
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+ offset, 0);
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+
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+- /* Jump to the end of TRX */
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++ /*
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++ * Try to find TRX size. The "length" field isn't fully
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++ * reliable as it could be decreased to make CRC32 cover
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++ * only part of TRX data. It's commonly used as checksum
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++ * can't cover e.g. ever-changing rootfs partition.
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++ * Use offsets as helpers for assuming min TRX size.
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++ */
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+ trx = (struct trx_header *)buf;
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+- offset = roundup(offset + trx->length, blocksize);
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+- /* Next loop iteration will increase the offset */
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+- offset -= blocksize;
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++ last_subpart = max3(trx->offset[0], trx->offset[1],
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++ trx->offset[2]);
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++ trx_size = max(trx->length, last_subpart + blocksize);
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++
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++ /*
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++ * Skip the TRX data. Decrease offset by block size as
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++ * the next loop iteration will increase it.
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++ */
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++ offset += roundup(trx_size, blocksize) - blocksize;
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+ continue;
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+ }
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+
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Rafał Miłecki