linux-kernel - [PATCH 5.4 360/453] crypto: arm/aes-ce - work around Cortex-A57/A72 silion errata

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Message-Id: <20201228124954.523837028@linuxfoundation.org>
Date:   Mon, 28 Dec 2020 13:49:56 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: [PATCH 5.4 360/453] crypto: arm/aes-ce - work around Cortex-A57/A72 silion errata

From: Ard Biesheuvel <ardb@...nel.org>

commit f3456b9fd269c6d0c973b136c5449d46b2510f4b upstream.

ARM Cortex-A57 and Cortex-A72 cores running in 32-bit mode are affected
by silicon errata #1742098 and #1655431, respectively, where the second
instruction of a AES instruction pair may execute twice if an interrupt
is taken right after the first instruction consumes an input register of
which a single 32-bit lane has been updated the last time it was modified.

This is not such a rare occurrence as it may seem: in counter mode, only
the least significant 32-bit word is incremented in the absence of a
carry, which makes our counter mode implementation susceptible to these
errata.

So let's shuffle the counter assignments around a bit so that the most
recent updates when the AES instruction pair executes are 128-bit wide.

[0] ARM-EPM-049219 v23 Cortex-A57 MPCore Software Developers Errata Notice
[1] ARM-EPM-012079 v11.0 Cortex-A72 MPCore Software Developers Errata Notice

Cc: <stable@...r.kernel.org> # v5.4+
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/arm/crypto/aes-ce-core.S |   32 ++++++++++++++++++++++----------
 1 file changed, 22 insertions(+), 10 deletions(-)

--- a/arch/arm/crypto/aes-ce-core.S
+++ b/arch/arm/crypto/aes-ce-core.S
@@ -386,20 +386,32 @@ ENTRY(ce_aes_ctr_encrypt)
 .Lctrloop4x:
 	subs		r4, r4, #4
 	bmi		.Lctr1x
-	add		r6, r6, #1
+
+	/*
+	 * NOTE: the sequence below has been carefully tweaked to avoid
+	 * a silicon erratum that exists in Cortex-A57 (#1742098) and
+	 * Cortex-A72 (#1655431) cores, where AESE/AESMC instruction pairs
+	 * may produce an incorrect result if they take their input from a
+	 * register of which a single 32-bit lane has been updated the last
+	 * time it was modified. To work around this, the lanes of registers
+	 * q0-q3 below are not manipulated individually, and the different
+	 * counter values are prepared by successive manipulations of q7.
+	 */
+	add		ip, r6, #1
 	vmov		q0, q7
+	rev		ip, ip
+	add		lr, r6, #2
+	vmov		s31, ip			@ set lane 3 of q1 via q7
+	add		ip, r6, #3
+	rev		lr, lr
 	vmov		q1, q7
-	rev		ip, r6
-	add		r6, r6, #1
+	vmov		s31, lr			@ set lane 3 of q2 via q7
+	rev		ip, ip
 	vmov		q2, q7
-	vmov		s7, ip
-	rev		ip, r6
-	add		r6, r6, #1
+	vmov		s31, ip			@ set lane 3 of q3 via q7
+	add		r6, r6, #4
 	vmov		q3, q7
-	vmov		s11, ip
-	rev		ip, r6
-	add		r6, r6, #1
-	vmov		s15, ip
+
 	vld1.8		{q4-q5}, [r1]!
 	vld1.8		{q6}, [r1]!
 	vld1.8		{q15}, [r1]!