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From: "Jürgen Groß" <jgross@suse.com>
To: Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org, "Paul E. McKenney" <paulmck@kernel.org>,
	Andy Lutomirski <luto@kernel.org>,
	Alexandre Chartre <alexandre.chartre@oracle.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Petr Mladek <pmladek@suse.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Joel Fernandes <joel@joelfernandes.org>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Brian Gerst <brgerst@gmail.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Will Deacon <will@kernel.org>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Wei Liu <wei.liu@kernel.org>,
	Michael Kelley <mikelley@microsoft.com>,
	Jason Chen CJ <jason.cj.chen@intel.com>,
	Zhao Yakui <yakui.zhao@intel.com>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>
Subject: Re: [patch V5 01/38] x86/kvm/svm: Use uninstrumented wrmsrl() to restore GS
Date: Wed, 13 May 2020 09:11:39 +0200	[thread overview]
Message-ID: <00ceab91-c86e-be17-0ac9-e4a45d8e7b25@suse.com> (raw)
In-Reply-To: <20200512213809.492016025@linutronix.de>

On 12.05.20 23:01, Thomas Gleixner wrote:
> On guest exit MSR_GS_BASE contains whatever the guest wrote to it and the
> first action after returning from the ASM code is to set it to the host
> kernel value. This uses wrmsrl() which is interesting at least.
> 
> wrmsrl() is either using native_write_msr() or the paravirt variant. The
> XEN_PV code is uninteresting as nested SVM in a XEN_PV guest does not work.
> 
> But native_write_msr() can be placed out of line by the compiler especially
> when paravirtualization is enabled in the kernel configuration. The
> function is marked notrace, but still can be probed if
> CONFIG_KPROBE_EVENTS_ON_NOTRACE is enabled.
> 
> That would be a fatal problem as kprobe events use per-CPU variables which
> are GS based and would be accessed with the guest GS. Depending on the GS
> value this would either explode in colorful ways or lead to completely
> undebugable data corruption.
> 
> Aside of that native_write_msr() contains a tracepoint which objtool
> complains about as it is invoked from the noinstr section.
> 
> As this cannot run inside a XEN_PV guest there is no point in using
> wrmsrl(). Use native_wrmsrl() instead which is just a plain native WRMSR
> without tracing or anything else attached.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Juergen Gross <jgross@suse.com>

Acked-by: Juergen Gross <jgross@suse.com>


Juergen

  reply	other threads:[~2020-05-13  7:11 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-12 21:00 [patch V5 00/38] x86/entry: Entry/exception code rework - the leftovers Thomas Gleixner
2020-05-12 21:01 ` [patch V5 01/38] x86/kvm/svm: Use uninstrumented wrmsrl() to restore GS Thomas Gleixner
2020-05-13  7:11   ` Jürgen Groß [this message]
2020-05-12 21:01 ` [patch V5 02/38] x86/entry/64: Use native swapgs in asm_native_load_gs_index() Thomas Gleixner
2020-05-13  2:02   ` Steven Rostedt
2020-05-13  6:34     ` Thomas Gleixner
2020-05-13  7:12   ` Jürgen Groß
2020-05-19 19:58   ` [tip: x86/entry] x86/entry/64: Use native swapgs in asm_load_gs_index() tip-bot2 for Thomas Gleixner
2020-05-12 21:01 ` [patch V5 03/38] nmi, tracing: Provide nmi_enter/exit_notrace() Thomas Gleixner
2020-05-15  1:32   ` Steven Rostedt
2020-05-15  1:35     ` Steven Rostedt
2020-05-15  1:37       ` Steven Rostedt
2020-05-12 21:01 ` [patch V5 04/38] x86: Make hardware latency tracing explicit Thomas Gleixner
2020-05-15  1:43   ` Steven Rostedt
2020-05-15 15:08     ` Thomas Gleixner
2020-05-12 21:01 ` [patch V5 05/38] genirq: Provide irq_enter/exit_rcu() Thomas Gleixner
2020-05-12 21:01 ` [patch V5 06/38] x86/entry: Provide helpers for execute on irqstack Thomas Gleixner
2020-05-13 21:43   ` Josh Poimboeuf
2020-05-12 21:01 ` [patch V5 07/38] x86/entry/64: Move do_softirq_own_stack() to C Thomas Gleixner
2020-05-12 21:01 ` [patch V5 08/38] x86/entry: Split idtentry_enter/exit() Thomas Gleixner
2020-05-12 21:01 ` [patch V5 09/38] x86/entry: Switch XEN/PV hypercall entry to IDTENTRY Thomas Gleixner
2020-05-14 16:24   ` Boris Ostrovsky
2020-05-12 21:01 ` [patch V5 10/38] x86/entry/64: Simplify idtentry_body Thomas Gleixner
2020-05-12 21:01 ` [patch V5 11/38] rcu: Provide __rcu_is_watching() Thomas Gleixner
2020-05-19 19:52   ` [tip: core/rcu] " tip-bot2 for Thomas Gleixner
2020-05-12 21:01 ` [patch V5 12/38] x86/entry: Provide idtentry_entry/exit_cond_rcu() Thomas Gleixner
2020-05-12 21:01 ` [patch V5 13/38] x86/entry: Switch page fault exception to IDTENTRY_RAW Thomas Gleixner
2020-05-12 21:01 ` [patch V5 14/38] x86/entry: Remove the transition leftovers Thomas Gleixner
2020-05-12 21:01 ` [patch V5 15/38] x86/entry: Change exit path of xen_failsafe_callback Thomas Gleixner
2020-05-12 21:01 ` [patch V5 16/38] x86/entry/64: Remove error_exit Thomas Gleixner
2020-05-12 21:01 ` [patch V5 17/38] x86/entry/32: Remove common_exception Thomas Gleixner
2020-05-12 21:01 ` [patch V5 18/38] x86/irq: Use generic irq_regs implementation Thomas Gleixner
2020-05-12 21:01 ` [patch V5 19/38] x86/irq: Convey vector as argument and not in ptregs Thomas Gleixner
2020-05-12 21:01 ` [patch V5 20/38] x86/irq/64: Provide handle_irq() Thomas Gleixner
2020-05-12 21:01 ` [patch V5 21/38] x86/entry: Add IRQENTRY_IRQ macro Thomas Gleixner
2020-05-12 21:01 ` [patch V5 22/38] x86/entry: Use idtentry for interrupts Thomas Gleixner
2020-05-12 21:01 ` [patch V5 23/38] genirq: Provde __irq_enter/exit_raw() Thomas Gleixner
2020-05-12 21:01 ` [patch V5 24/38] x86/entry: Provide IDTENTRY_SYSVEC Thomas Gleixner
2020-05-15  0:16   ` Boris Ostrovsky
2020-05-15  8:52     ` Thomas Gleixner
2020-05-12 21:01 ` [patch V5 25/38] x86/entry: Convert APIC interrupts to IDTENTRY_SYSVEC Thomas Gleixner
2020-05-12 21:01 ` [patch V5 26/38] x86/entry: Convert SMP system vectors " Thomas Gleixner
2020-05-12 21:01 ` [patch V5 27/38] x86/entry: Convert various system vectors Thomas Gleixner
2020-05-12 21:01 ` [patch V5 28/38] x86/entry: Convert KVM vectors to IDTENTRY_SYSVEC Thomas Gleixner
2020-05-12 21:01 ` [patch V5 29/38] x86/entry: Convert various hypervisor " Thomas Gleixner
2020-05-12 21:01 ` [patch V5 30/38] x86/entry: Convert XEN hypercall vector " Thomas Gleixner
2020-05-12 21:01 ` [patch V5 31/38] x86/entry: Convert reschedule interrupt to IDTENTRY_SYSVEC_SIMPLE Thomas Gleixner
2020-05-12 21:01 ` [patch V5 32/38] x86/entry: Remove the apic/BUILD interrupt leftovers Thomas Gleixner
2020-05-12 21:01 ` [patch V5 33/38] x86/entry/64: Remove IRQ stack switching ASM Thomas Gleixner
2020-05-12 21:01 ` [patch V5 34/38] x86/entry: Make enter_from_user_mode() static Thomas Gleixner
2020-05-12 21:01 ` [patch V5 35/38] x86/entry/32: Remove redundant irq disable code Thomas Gleixner
2020-05-12 21:01 ` [patch V5 36/38] x86/entry/64: Remove TRACE_IRQS_*_DEBUG Thomas Gleixner
2020-05-12 21:01 ` [patch V5 37/38] x86/entry: Move paranoid irq tracing out of ASM code Thomas Gleixner
2020-05-12 21:01 ` [patch V5 38/38] x86/entry: Remove the TRACE_IRQS cruft Thomas Gleixner
2020-05-14 16:35 ` [patch V5 00/38] x86/entry: Entry/exception code rework - the leftovers Paul E. McKenney

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