commit 2decad92f4731fac9755a083fcfefa66edb7d67d upstream.

The entry from EL0 code checks the TFSRE0_EL1 register for any asynchronous tag check faults in user space and sets the TIF_MTE_ASYNC_FAULT flag. This is not done atomically, potentially racing with another CPU calling set_tsk_thread_flag().

Replace the non-atomic ORR+STR with an STSET instruction. While STSET requires ARMv8.1 and an assembler that understands LSE atomics, the MTE feature is part of ARMv8.5 and already requires an updated assembler.

Signed-off-by: Catalin Marinas catalin.marinas@arm.com Fixes: 637ec831ea4f ("arm64: mte: Handle synchronous and asynchronous tag check faults") Cc: stable@vger.kernel.org # 5.10.x Reported-by: Will Deacon will@kernel.org Cc: Will Deacon will@kernel.org Cc: Vincenzo Frascino vincenzo.frascino@arm.com Cc: Mark Rutland mark.rutland@arm.com Link: https://lore.kernel.org/r/20210409173710.18582-1-catalin.marinas@arm.com Signed-off-by: Will Deacon will@kernel.org --- arch/arm64/Kconfig | 6 +++++- arch/arm64/kernel/entry.S | 10 ++++++---- 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index c1be64228327..5e5cf3af6351 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1390,10 +1390,13 @@ config ARM64_PAN The feature is detected at runtime, and will remain as a 'nop' instruction if the cpu does not implement the feature.

+config AS_HAS_LSE_ATOMICS + def_bool $(as-instr,.arch_extension lse) + config ARM64_LSE_ATOMICS bool default ARM64_USE_LSE_ATOMICS - depends on $(as-instr,.arch_extension lse) + depends on AS_HAS_LSE_ATOMICS

config ARM64_USE_LSE_ATOMICS bool "Atomic instructions" @@ -1667,6 +1670,7 @@ config ARM64_MTE bool "Memory Tagging Extension support" default y depends on ARM64_AS_HAS_MTE && ARM64_TAGGED_ADDR_ABI + depends on AS_HAS_LSE_ATOMICS select ARCH_USES_HIGH_VMA_FLAGS help Memory Tagging (part of the ARMv8.5 Extensions) provides diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index d72c818b019c..2da82c139e1c 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -148,16 +148,18 @@ alternative_cb_end .endm

/* Check for MTE asynchronous tag check faults */ - .macro check_mte_async_tcf, flgs, tmp + .macro check_mte_async_tcf, tmp, ti_flags #ifdef CONFIG_ARM64_MTE + .arch_extension lse alternative_if_not ARM64_MTE b 1f alternative_else_nop_endif mrs_s \tmp, SYS_TFSRE0_EL1 tbz \tmp, #SYS_TFSR_EL1_TF0_SHIFT, 1f /* Asynchronous TCF occurred for TTBR0 access, set the TI flag */ - orr \flgs, \flgs, #_TIF_MTE_ASYNC_FAULT - str \flgs, [tsk, #TSK_TI_FLAGS] + mov \tmp, #_TIF_MTE_ASYNC_FAULT + add \ti_flags, tsk, #TSK_TI_FLAGS + stset \tmp, [\ti_flags] msr_s SYS_TFSRE0_EL1, xzr 1: #endif @@ -207,7 +209,7 @@ alternative_else_nop_endif disable_step_tsk x19, x20

/* Check for asynchronous tag check faults in user space */ - check_mte_async_tcf x19, x22 + check_mte_async_tcf x22, x23 apply_ssbd 1, x22, x23

ptrauth_keys_install_kernel tsk, x20, x22, x23