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arm64: trap to EL1 accesses to AMU counters from EL0

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The activity monitors extension is an optional extension introduced
by the ARMv8.4 CPU architecture. In order to access the activity
monitors counters safely, if desired, the kernel should detect the
presence of the extension through the feature register, and mediate
the access.

Therefore, disable direct accesses to activity monitors counters
from EL0 (userspace) and trap them to EL1 (kernel).

To be noted that the ARM64_AMU_EXTN kernel config does not have an
effect on this code. Given that the amuserenr_el0 resets to an
UNKNOWN value, setting the trap of EL0 accesses to EL1 is always
attempted for safety and security considerations. Therefore firmware
should still ensure accesses to AMU registers are not trapped in
EL2/EL3 as this code cannot be bypassed if the CPU implements the
Activity Monitors Unit.

Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Reviewed-by: James Morse <james.morse@arm.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Steve Capper <steve.capper@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Ionela Voinescu 2020-03-05 09:06:22 +00:00 committed by Catalin Marinas
parent 2c9d45b43c
commit 87a1f06346
2 changed files with 13 additions and 0 deletions
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10
arch/arm64/include/asm/assembler.h
View file

@ -430,6 +430,16 @@ USER(\label, ic ivau, \tmp2) // invalidate I line PoU
9000:
.endm
/*
* reset_amuserenr_el0 - reset AMUSERENR_EL0 if AMUv1 present
*/
.macro reset_amuserenr_el0, tmpreg
mrs \tmpreg, id_aa64pfr0_el1 // Check ID_AA64PFR0_EL1
ubfx \tmpreg, \tmpreg, #ID_AA64PFR0_AMU_SHIFT, #4
cbz \tmpreg, .Lskip_\@ // Skip if no AMU present
msr_s SYS_AMUSERENR_EL0, xzr // Disable AMU access from EL0
.Lskip_\@:
.endm
/*
* copy_page - copy src to dest using temp registers t1-t8
*/

3
arch/arm64/mm/proc.S
View file

@ -131,6 +131,7 @@ alternative_endif
ubfx x11, x11, #1, #1
msr oslar_el1, x11
reset_pmuserenr_el0 x0 // Disable PMU access from EL0
reset_amuserenr_el0 x0 // Disable AMU access from EL0
alternative_if ARM64_HAS_RAS_EXTN
msr_s SYS_DISR_EL1, xzr
@ -423,6 +424,8 @@ SYM_FUNC_START(__cpu_setup)
isb // Unmask debug exceptions now,
enable_dbg // since this is per-cpu
reset_pmuserenr_el0 x0 // Disable PMU access from EL0
reset_amuserenr_el0 x0 // Disable AMU access from EL0
/*
* Memory region attributes
*/