[PATCH] arm64: mte: initialize RGSR_EL1.SEED in __cpu_setup

[Peter Collingbourne]

A valid implementation choice for the ChooseRandomNonExcludedTag()
pseudocode function used by IRG is to behave in the same way as with
GCR_EL1.RRND=0. This would mean that RGSR_EL1.SEED is used as an LFSR
which must have a non-zero value in order for IRG to properly produce
pseudorandom numbers. However, RGSR_EL1 is reset to an UNKNOWN value
on soft reset and thus may reset to 0. Therefore we must initialize
RGSR_EL1.SEED to a non-zero value in order to ensure that IRG behaves
as expected.

Signed-off-by: Peter Collingbourne <pcc at google.com>
Cc: stable at vger.kernel.org
Link: https://linux-review.googlesource.com/id/I2b089b6c7d6f17ee37e2f0db7df5ad5bcc04526c
---
 arch/arm64/mm/proc.S | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 0a48191534ff..e8e1eaee4b3f 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -437,7 +437,7 @@ SYM_FUNC_START(__cpu_setup)
 	mrs	x10, ID_AA64PFR1_EL1
 	ubfx	x10, x10, #ID_AA64PFR1_MTE_SHIFT, #4
 	cmp	x10, #ID_AA64PFR1_MTE
-	b.lt	1f
+	b.lt	2f
 
 	/* Normal Tagged memory type at the corresponding MAIR index */
 	mov	x10, #MAIR_ATTR_NORMAL_TAGGED
@@ -447,6 +447,19 @@ SYM_FUNC_START(__cpu_setup)
 	mov	x10, #(SYS_GCR_EL1_RRND | SYS_GCR_EL1_EXCL_MASK)
 	msr_s	SYS_GCR_EL1, x10
 
+	/*
+	 * Initialize RGSR_EL1.SEED to a non-zero value. If the implementation
+	 * chooses to implement GCR_EL1.RRND=1 in the same way as RRND=0 then
+	 * the seed will be used as an LFSR, so it should be put onto the MLS.
+	 */
+	mrs	x10, CNTVCT_EL0
+	and	x10, x10, #SYS_RGSR_EL1_SEED_MASK
+	cbnz	x10, 1f
+	mov	x10, #1
+1:
+	lsl	x10, x10, #SYS_RGSR_EL1_SEED_SHIFT
+	msr_s	SYS_RGSR_EL1, x10
+
 	/* clear any pending tag check faults in TFSR*_EL1 */
 	msr_s	SYS_TFSR_EL1, xzr
 	msr_s	SYS_TFSRE0_EL1, xzr
@@ -454,7 +467,7 @@ SYM_FUNC_START(__cpu_setup)
 	/* set the TCR_EL1 bits */
 	mov_q	x10, TCR_KASAN_HW_FLAGS
 	orr	tcr, tcr, x10
-1:
+2:
 #endif
 	tcr_clear_errata_bits tcr, x9, x5
 
-- 
2.31.1.607.g51e8a6a459-goog