Commit 9de6fe3c authored Apr 10, 2020 by Xiaoyao Li Committed by Borislav Petkov Apr 11, 2020

KVM: x86: Emulate split-lock access as a write in emulator

Emulate split-lock accesses as writes if split lock detection is on
to avoid #AC during emulation, which will result in a panic(). This
should never occur for a well-behaved guest, but a malicious guest can
manipulate the TLB to trigger emulation of a locked instruction[1].

More discussion can be found at [2][3].

[1] https://lkml.kernel.org/r/8c5b11c9-58df-38e7-a514-dc12d687b198@redhat.com
[2] https://lkml.kernel.org/r/20200131200134.GD18946@linux.intel.com
[3] https://lkml.kernel.org/r/20200227001117.GX9940@linux.intel.com



Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lkml.kernel.org/r/20200410115517.084300242@linutronix.de

parent d7e94dbd

arch/x86/kvm/x86.c

+11 −1

Original line number	Diff line number	Diff line
		@@ -5839,6 +5839,7 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
		{
		struct kvm_host_map map;
		struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
		u64 page_line_mask;
		gpa_t gpa;
		char *kaddr;
		bool exchanged;
		@@ -5853,7 +5854,16 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
		(gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE)
		goto emul_write;

		if (((gpa + bytes - 1) & PAGE_MASK) != (gpa & PAGE_MASK))
		/*
		* Emulate the atomic as a straight write to avoid #AC if SLD is
		* enabled in the host and the access splits a cache line.
		*/
		if (boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT))
		page_line_mask = ~(cache_line_size() - 1);
		else
		page_line_mask = PAGE_MASK;

		if (((gpa + bytes - 1) & page_line_mask) != (gpa & page_line_mask))
		goto emul_write;

		if (kvm_vcpu_map(vcpu, gpa_to_gfn(gpa), &map))

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