x86/iopl/64: Properly context-switch IOPL on Xen PV (b7a58459) · Commits · 戴 / test

On Xen PV, regs->flags doesn't reliably reflect IOPL and the exit-to-userspace code doesn't change IOPL. We need to context switch it manually. I'm doing this without going through paravirt because this is specific to Xen PV. After the dust settles, we can merge this with the 32-bit code, tidy up the iopl syscall implementation, and remove the set_iopl pvop entirely. Fixes XSA-171. Reviewewd-by:

Jan Beulich <JBeulich@suse.com> Signed-off-by:

Andy Lutomirski <luto@kernel.org> Cc: Andrew Cooper <andrew.cooper3@citrix.com> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: David Vrabel <david.vrabel@citrix.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Jan Beulich <JBeulich@suse.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/693c3bd7aeb4d3c27c92c622b7d0f554a458173c.1458162709.git.luto@kernel.org Signed-off-by:

Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/xen/hypervisor.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -62,4 +62,6 @@ void xen_arch_register_cpu(int num);
		void xen_arch_unregister_cpu(int num);
		#endif

		extern void xen_set_iopl_mask(unsigned mask);

		#endif /* _ASM_X86_XEN_HYPERVISOR_H */

arch/x86/kernel/process_64.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -48,6 +48,7 @@
		#include <asm/syscalls.h>
		#include <asm/debugreg.h>
		#include <asm/switch_to.h>
		#include <asm/xen/hypervisor.h>

		asmlinkage extern void ret_from_fork(void);

		@@ -411,6 +412,17 @@ __switch_to(struct task_struct prev_p, struct task_struct next_p)
		task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV))
		__switch_to_xtra(prev_p, next_p, tss);

		#ifdef CONFIG_XEN
		/*
		* On Xen PV, IOPL bits in pt_regs->flags have no effect, and
		* current_pt_regs()->flags may not match the current task's
		* intended IOPL. We need to switch it manually.
		*/
		if (unlikely(static_cpu_has(X86_FEATURE_XENPV) &&
		prev->iopl != next->iopl))
		xen_set_iopl_mask(next->iopl);
		#endif

		if (static_cpu_has_bug(X86_BUG_SYSRET_SS_ATTRS)) {
		/*
		* AMD CPUs have a misfeature: SYSRET sets the SS selector but

arch/x86/xen/enlighten.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -961,7 +961,7 @@ static void xen_load_sp0(struct tss_struct *tss,
		tss->x86_tss.sp0 = thread->sp0;
		}

		static void xen_set_iopl_mask(unsigned mask)
		void xen_set_iopl_mask(unsigned mask)
		{
		struct physdev_set_iopl set_iopl;

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