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From: Mark Rutland <mark.rutland@arm.com>
To: linux-arm-kernel@lists.infradead.org
Cc: mark.rutland@arm.com, elver@google.com, paulmck@kernel.org,
	peterz@infradead.org, catalin.marinas@arm.com,
	james.morse@arm.com, will@kernel.org, dvyukov@google.com
Subject: [PATCH 01/11] arm64: syscall: exit userspace before unmasking exceptions
Date: Thu, 26 Nov 2020 12:35:52 +0000	[thread overview]
Message-ID: <20201126123602.23454-2-mark.rutland@arm.com> (raw)
In-Reply-To: <20201126123602.23454-1-mark.rutland@arm.com>

In el0_svc_common() we unmask exceptions before we call user_exit(), and
so there's a window where an IRQ or debug exception can be taken while
RCU is not watching. In do_debug_exception() we account for this in via
debug_exception_{enter,exit}(), but in the el1_irq asm we do not and we
call trace functions which rely on RCU before we have a guarantee that
RCU is watching.

Let's avoid this by having el0_svc_common() exit userspace before
unmasking exceptions, matching what we do for all other EL0 entry paths.
We can use user_exit_irqoff() to avoid the pointless save/restore of IRQ
flags while we're sure exceptions are masked in DAIF.

The workaround for Cortex-A76 erratum 1463225 may trigger a debug
exception before this point, but the debug code invoked in this case is
safe even when RCU is not watching.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/syscall.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index e4c0dadf0d92..13fe79f8e2db 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -120,8 +120,8 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 	 */
 
 	cortex_a76_erratum_1463225_svc_handler();
+	user_exit_irqoff();
 	local_daif_restore(DAIF_PROCCTX);
-	user_exit();
 
 	if (system_supports_mte() && (flags & _TIF_MTE_ASYNC_FAULT)) {
 		/*
-- 
2.11.0


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  reply	other threads:[~2020-11-26 12:38 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-26 12:35 [PATCH 00/11] arm64: entry lockdep/rcu/tracing fixes Mark Rutland
2020-11-26 12:35 ` Mark Rutland [this message]
2020-11-26 12:35 ` [PATCH 02/11] arm64: mark idle code as noinstr Mark Rutland
2020-11-26 12:35 ` [PATCH 03/11] arm64: entry: mark entry " Mark Rutland
2020-11-26 12:35 ` [PATCH 04/11] arm64: entry: move enter_from_user_mode to entry-common.c Mark Rutland
2020-11-26 12:35 ` [PATCH 05/11] arm64: entry: prepare ret_to_user for function call Mark Rutland
2020-11-26 12:35 ` [PATCH 06/11] arm64: entry: move el1 irq/nmi logic to C Mark Rutland
2020-11-26 12:35 ` [PATCH 07/11] arm64: entry: fix non-NMI user<->kernel transitions Mark Rutland
2020-11-30 11:22   ` Will Deacon
2020-11-26 12:35 ` [PATCH 08/11] arm64: ptrace: prepare for EL1 irq/rcu tracking Mark Rutland
2020-11-30 11:01   ` Will Deacon
2020-11-26 12:36 ` [PATCH 09/11] arm64: entry: fix non-NMI kernel<->kernel transitions Mark Rutland
2020-11-30 11:22   ` Will Deacon
2020-11-26 12:36 ` [PATCH 10/11] arm64: entry: fix NMI {user, kernel}->kernel transitions Mark Rutland
2020-11-26 18:41   ` [PATCH 10/11] arm64: entry: fix NMI {user,kernel}->kernel transitions Mark Rutland
2020-11-26 21:00     ` Will Deacon
2020-11-26 12:36 ` [PATCH 11/11] arm64: entry: fix EL1 debug transitions Mark Rutland
2020-11-30 11:23 ` [PATCH 00/11] arm64: entry lockdep/rcu/tracing fixes Will Deacon
2020-11-30 12:03 ` Marco Elver
2020-11-30 12:38   ` Mark Rutland
     [not found]     ` <20201130133245.GA1307615@elver.google.com>
2020-11-30 16:54       ` Mark Rutland

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