x86, 64-bit: swapgs pvop with a user-stack can never be called
It's never safe to call a swapgs pvop when the user stack is current - it must be inline replaced. Rather than making a call, the SWAPGS_UNSAFE_STACK pvop always just puts "swapgs" as a placeholder, which must either be replaced inline or trap'n'emulated (somehow). Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> Cc: xen-devel <xen-devel@lists.xensource.com> Cc: Stephen Tweedie <sct@redhat.com> Cc: Eduardo Habkost <ehabkost@redhat.com> Cc: Mark McLoughlin <markmc@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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2 changed files with 11 additions and 1 deletions
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@ -111,6 +111,7 @@ static inline unsigned long __raw_local_irq_save(void)
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#define DISABLE_INTERRUPTS(x) cli
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#ifdef CONFIG_X86_64
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#define SWAPGS_UNSAFE_STACK swapgs
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#define INTERRUPT_RETURN iretq
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#define USERGS_SYSRET64 \
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swapgs; \
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@ -185,7 +186,6 @@ static inline void trace_hardirqs_fixup(void)
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* Either way, this is a good way to document that we don't
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* have a reliable stack. x86_64 only.
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*/
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#define SWAPGS_UNSAFE_STACK swapgs
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#define ARCH_TRACE_IRQS_ON call trace_hardirqs_on_thunk
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#define ARCH_TRACE_IRQS_OFF call trace_hardirqs_off_thunk
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#define ARCH_LOCKDEP_SYS_EXIT call lockdep_sys_exit_thunk
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@ -1522,6 +1522,16 @@ static inline unsigned long __raw_local_irq_save(void)
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#else /* !CONFIG_X86_32 */
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/*
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* If swapgs is used while the userspace stack is still current,
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* there's no way to call a pvop. The PV replacement *must* be
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* inlined, or the swapgs instruction must be trapped and emulated.
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*/
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#define SWAPGS_UNSAFE_STACK \
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PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_swapgs), CLBR_NONE, \
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swapgs)
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#define SWAPGS \
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PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_swapgs), CLBR_NONE, \
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PV_SAVE_REGS; \
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