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@xxxxxxxxxxxxxxx> # v5.4+
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
---
v2: - add comment block describing the erratum and how it is being worked
around
- mention A57 as well as A72, as both are affected
arch/arm/crypto/aes-ce-core.S | 32 ++++++++++++++------
1 file changed, 22 insertions(+), 10 deletions(-)
diff --git a/arch/arm/crypto/aes-ce-core.S b/arch/arm/crypto/aes-ce-core.S
index 4d1707388d94..312428d83eed 100644
--- 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]!
--
2.17.1
