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@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx 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
