Subject: [PATCH net-next v2 7/7] net: ipa: avoid field overflow

From: Alex Elder <[email-masked]>
Date: Fri, 5 Feb 2021 16:11:00 -0600

It's possible that the length passed to ipa_header_size_encoded()
is larger than what can be represented by the HDR_LEN field alone
(starting with IPA v4.5).  If we attempted that, u32_encode_bits()
would trigger a build-time error.

Avoid this problem by masking off high-order bits of the value
encoded as the lower portion of the header length.

The same sort of problem exists in ipa_metadata_offset_encoded(),
so implement the same fix there.

Signed-off-by: Alex Elder <[email-masked]>
---
 drivers/net/ipa/ipa_reg.h | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ipa/ipa_reg.h b/drivers/net/ipa/ipa_reg.h
index e6b0827a244ec..732e691e9aa62 100644
--- a/drivers/net/ipa/ipa_reg.h
+++ b/drivers/net/ipa/ipa_reg.h
@@ -408,15 +408,18 @@ enum ipa_cs_offload_en {
 static inline u32 ipa_header_size_encoded(enum ipa_version version,
 					  u32 header_size)
 {
+	u32 size = header_size & field_mask(HDR_LEN_FMASK);
 	u32 val;
 
-	val = u32_encode_bits(header_size, HDR_LEN_FMASK);
-	if (version < IPA_VERSION_4_5)
+	val = u32_encode_bits(size, HDR_LEN_FMASK);
+	if (version < IPA_VERSION_4_5) {
+		/* ipa_assert(header_size == size); */
 		return val;
+	}
 
 	/* IPA v4.5 adds a few more most-significant bits */
-	header_size >>= hweight32(HDR_LEN_FMASK);
-	val |= u32_encode_bits(header_size, HDR_LEN_MSB_FMASK);
+	size = header_size >> hweight32(HDR_LEN_FMASK);
+	val |= u32_encode_bits(size, HDR_LEN_MSB_FMASK);
 
 	return val;
 }
@@ -425,15 +428,18 @@ static inline u32 ipa_header_size_encoded(enum ipa_version version,
 static inline u32 ipa_metadata_offset_encoded(enum ipa_version version,
 					      u32 offset)
 {
+	u32 off = offset & field_mask(HDR_OFST_METADATA_FMASK);
 	u32 val;
 
-	val = u32_encode_bits(offset, HDR_OFST_METADATA_FMASK);
-	if (version < IPA_VERSION_4_5)
+	val = u32_encode_bits(off, HDR_OFST_METADATA_FMASK);
+	if (version < IPA_VERSION_4_5) {
+		/* ipa_assert(offset == off); */
 		return val;
+	}
 
 	/* IPA v4.5 adds a few more most-significant bits */
-	offset >>= hweight32(HDR_OFST_METADATA_FMASK);
-	val |= u32_encode_bits(offset, HDR_OFST_METADATA_MSB_FMASK);
+	off = offset >> hweight32(HDR_OFST_METADATA_FMASK);
+	val |= u32_encode_bits(off, HDR_OFST_METADATA_MSB_FMASK);
 
 	return val;
 }
-- 
2.20.1