[PATCH 5.11 063/122] arm64: mte: Ensure TIF_MTE_ASYNC_FAULT is set atomically

Greg Kroah-Hartman
2021-04-19T13:12:19Z

From: Catalin Marinas <catalin.marinas@arm.com>

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm64/Kconfig | 6 +++++-
arch/arm64/kernel/entry.S | 10 ++++++----
2 files changed, 11 insertions(+), 5 deletions(-)

--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1399,10 +1399,13 @@ config ARM64_PAN
config AS_HAS_LDAPR
def_bool $(as-instr,.arch_extension rcpc)

+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"
@@ -1659,6 +1662,7 @@ config ARM64_MTE
default y
depends on ARM64_AS_HAS_MTE && ARM64_TAGGED_ADDR_ABI
depends on AS_HAS_ARMV8_5
+ depends on AS_HAS_LSE_ATOMICS
# Required for tag checking in the uaccess routines
depends on ARM64_PAN
select ARCH_USES_HIGH_VMA_FLAGS
--- 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
@@ -244,7 +246,7 @@ 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