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arm64: mte: initialize RGSR_EL1.SEED in __cpu_setup 

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@google.com>
Fixes: 3b714d24ef ("arm64: mte: CPU feature detection and initial sysreg configuration")
Cc: <stable@vger.kernel.org> # 5.10
Link: https://linux-review.googlesource.com/id/I2b089b6c7d6f17ee37e2f0db7df5ad5bcc04526c
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20210507185905.1745402-1-pcc@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Peter Collingbourne 2021-05-07 11:59:05 -07:00 committed by Catalin Marinas
parent a1bed090fc
commit 37a8024d26
1 changed files with 12 additions and 0 deletions
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12
arch/arm64/mm/proc.S
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@ -447,6 +447,18 @@ SYM_FUNC_START(__cpu_setup)
mov x10, #(SYS_GCR_EL1_RRND | SYS_GCR_EL1_EXCL_MASK)
msr_s SYS_GCR_EL1, x10
/*
* If GCR_EL1.RRND=1 is implemented the same way as RRND=0, then
* RGSR_EL1.SEED must be non-zero for IRG to produce
* pseudorandom numbers. As RGSR_EL1 is UNKNOWN out of reset, we
* must initialize it.
*/
mrs x10, CNTVCT_EL0
ands x10, x10, #SYS_RGSR_EL1_SEED_MASK
csinc x10, x10, xzr, ne
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