From: Sasha Levin <sashal@kernel.org> To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Mark Rutland <mark.rutland@arm.com>, Catalin Marinas <catalin.marinas@arm.com>, James Morse <james.morse@arm.com>, Will Deacon <will@kernel.org>, Sasha Levin <sashal@kernel.org>, linux-arm-kernel@lists.infradead.org Subject: [PATCH AUTOSEL 4.19 4/9] arm64: syscall: exit userspace before unmasking exceptions Date: Sat, 12 Dec 2020 11:08:43 -0500 [thread overview] Message-ID: <20201212160848.2335307-4-sashal@kernel.org> (raw) In-Reply-To: <20201212160848.2335307-1-sashal@kernel.org> From: Mark Rutland <mark.rutland@arm.com> [ Upstream commit ca1314d73eed493c49bb1932c60a8605530db2e4 ] 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> Link: https://lore.kernel.org/r/20201130115950.22492-2-mark.rutland@arm.com Signed-off-by: Will Deacon <will@kernel.org> Signed-off-by: Sasha Levin <sashal@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 1457a0ba83dbc..f2d2dbbbfca20 100644 --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -102,8 +102,8 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, regs->syscallno = scno; cortex_a76_erratum_1463225_svc_handler(); + user_exit_irqoff(); local_daif_restore(DAIF_PROCCTX); - user_exit(); if (has_syscall_work(flags)) { /* set default errno for user-issued syscall(-1) */ -- 2.27.0
WARNING: multiple messages have this Message-ID (diff)
From: Sasha Levin <sashal@kernel.org> To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Mark Rutland <mark.rutland@arm.com>, Sasha Levin <sashal@kernel.org>, Catalin Marinas <catalin.marinas@arm.com>, James Morse <james.morse@arm.com>, Will Deacon <will@kernel.org>, linux-arm-kernel@lists.infradead.org Subject: [PATCH AUTOSEL 4.19 4/9] arm64: syscall: exit userspace before unmasking exceptions Date: Sat, 12 Dec 2020 11:08:43 -0500 [thread overview] Message-ID: <20201212160848.2335307-4-sashal@kernel.org> (raw) In-Reply-To: <20201212160848.2335307-1-sashal@kernel.org> From: Mark Rutland <mark.rutland@arm.com> [ Upstream commit ca1314d73eed493c49bb1932c60a8605530db2e4 ] 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> Link: https://lore.kernel.org/r/20201130115950.22492-2-mark.rutland@arm.com Signed-off-by: Will Deacon <will@kernel.org> Signed-off-by: Sasha Levin <sashal@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 1457a0ba83dbc..f2d2dbbbfca20 100644 --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -102,8 +102,8 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, regs->syscallno = scno; cortex_a76_erratum_1463225_svc_handler(); + user_exit_irqoff(); local_daif_restore(DAIF_PROCCTX); - user_exit(); if (has_syscall_work(flags)) { /* set default errno for user-issued syscall(-1) */ -- 2.27.0 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-12-12 16:26 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-12-12 16:08 [PATCH AUTOSEL 4.19 1/9] drm/tegra: replace idr_init() by idr_init_base() Sasha Levin 2020-12-12 16:08 ` Sasha Levin 2020-12-12 16:08 ` [PATCH AUTOSEL 4.19 2/9] kernel/cpu: add arch override for clear_tasks_mm_cpumask() mm handling Sasha Levin 2020-12-12 16:08 ` [PATCH AUTOSEL 4.19 3/9] drm/tegra: sor: Disable clocks on error in tegra_sor_init() Sasha Levin 2020-12-12 16:08 ` Sasha Levin 2020-12-12 16:08 ` Sasha Levin [this message] 2020-12-12 16:08 ` [PATCH AUTOSEL 4.19 4/9] arm64: syscall: exit userspace before unmasking exceptions Sasha Levin 2020-12-12 16:08 ` [PATCH AUTOSEL 4.19 5/9] vxlan: Add needed_headroom for lower device Sasha Levin 2020-12-12 16:08 ` [PATCH AUTOSEL 4.19 6/9] vxlan: Copy needed_tailroom from lowerdev Sasha Levin 2020-12-12 16:08 ` [PATCH AUTOSEL 4.19 7/9] scsi: storvsc: Validate length of incoming packet in storvsc_on_channel_callback() Sasha Levin 2020-12-12 16:08 ` Sasha Levin 2020-12-12 16:08 ` [PATCH AUTOSEL 4.19 8/9] scsi: mpt3sas: Increase IOCInit request timeout to 30s Sasha Levin 2020-12-12 16:08 ` [PATCH AUTOSEL 4.19 9/9] dm table: Remove BUG_ON(in_interrupt()) Sasha Levin 2020-12-12 16:08 ` [dm-devel] " Sasha Levin
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