scsi: ufs: core: Add UFSHCD_QUIRK_KEYS_IN_PRDT

Since the nonstandard inline encryption support on Exynos SoCs requires
that raw cryptographic keys be copied into the PRDT, it is desirable to
zeroize those keys after each request to keep them from being left in
memory.  Therefore, add a quirk bit that enables the zeroization.

We could instead do the zeroization unconditionally.  However, using a
quirk bit avoids adding the zeroization overhead to standard devices.

Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20240708235330.103590-6-ebiggers@kernel.org
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/ufs/core/ufshcd-crypto.h

@@ -50,6 +50,20 @@ static inline int ufshcd_crypto_fill_prdt(struct ufs_hba *hba,
 	return 0;
 }
 
+static inline void ufshcd_crypto_clear_prdt(struct ufs_hba *hba,
+					    struct ufshcd_lrb *lrbp)
+{
+	if (!(hba->quirks & UFSHCD_QUIRK_KEYS_IN_PRDT))
+		return;
+
+	if (!(scsi_cmd_to_rq(lrbp->cmd)->crypt_ctx))
+		return;
+
+	/* Zeroize the PRDT because it can contain cryptographic keys. */
+	memzero_explicit(lrbp->ucd_prdt_ptr,
+			 ufshcd_sg_entry_size(hba) * scsi_sg_count(lrbp->cmd));
+}
+
 bool ufshcd_crypto_enable(struct ufs_hba *hba);
 
 int ufshcd_hba_init_crypto_capabilities(struct ufs_hba *hba);
@@ -73,6 +87,9 @@ static inline int ufshcd_crypto_fill_prdt(struct ufs_hba *hba,
 	return 0;
 }
 
+static inline void ufshcd_crypto_clear_prdt(struct ufs_hba *hba,
+					    struct ufshcd_lrb *lrbp) { }
+
 static inline bool ufshcd_crypto_enable(struct ufs_hba *hba)
 {
 	return false;

drivers/ufs/core/ufshcd.c

@@ -5479,6 +5479,7 @@ void ufshcd_release_scsi_cmd(struct ufs_hba *hba,
 	struct scsi_cmnd *cmd = lrbp->cmd;
 
 	scsi_dma_unmap(cmd);
+	ufshcd_crypto_clear_prdt(hba, lrbp);
 	ufshcd_release(hba);
 	ufshcd_clk_scaling_update_busy(hba);
 }

include/ufs/ufshcd.h

@@ -665,6 +665,14 @@ enum ufshcd_quirks {
 	 * host controller initialization fails if that bit is set.
 	 */
 	UFSHCD_QUIRK_BROKEN_CRYPTO_ENABLE		= 1 << 23,
+
+	/*
+	 * This quirk needs to be enabled if the host controller driver copies
+	 * cryptographic keys into the PRDT in order to send them to hardware,
+	 * and therefore the PRDT should be zeroized after each request (as per
+	 * the standard best practice for managing keys).
+	 */
+	UFSHCD_QUIRK_KEYS_IN_PRDT			= 1 << 24,
 };
 
 enum ufshcd_caps {