44 lines
1.6 KiB
Diff
44 lines
1.6 KiB
Diff
From patchwork Tue Jun 5 20:04:16 2018
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Content-Type: text/plain; charset="utf-8"
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MIME-Version: 1.0
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Content-Transfer-Encoding: 7bit
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Subject: kvm: x86: Check CPL in segmented_write_std
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From: Bandan Das <bsd@redhat.com>
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X-Patchwork-Id: 10449159
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Message-Id: <jpgtvqhuhj3.fsf@linux.bootlegged.copy>
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To: kvm@vger.kernel.org
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Cc: Paolo Bonzini <pbonzini@redhat.com>,
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Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
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Andy Lutomirski <luto@kernel.org>
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Date: Tue, 05 Jun 2018 16:04:16 -0400
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Certain instructions such as sgdt/sidt call segmented_write_std that
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doesn't propagate access correctly. As such, during userspace induced
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exception, the guest can incorrectly assume that the exception
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happened in the kernel and panic. The emulated write function
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segmented_write does seem to check access correctly.
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Reported-by: Andy Lutomirski <luto@kernel.org>
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Signed-off-by: Bandan Das <bsd@redhat.com>
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---
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arch/x86/kvm/x86.c | 3 ++-
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1 file changed, 2 insertions(+), 1 deletion(-)
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diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
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index 71e7cda6d014..871265f6a35f 100644
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--- a/arch/x86/kvm/x86.c
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+++ b/arch/x86/kvm/x86.c
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@@ -4824,10 +4824,11 @@ int kvm_write_guest_virt_system(struct x86_emulate_ctxt *ctxt,
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struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt);
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void *data = val;
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int r = X86EMUL_CONTINUE;
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+ u32 access = (kvm_x86_ops->get_cpl(vcpu) == 3) ? PFERR_USER_MASK : 0;
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while (bytes) {
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gpa_t gpa = vcpu->arch.walk_mmu->gva_to_gpa(vcpu, addr,
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- PFERR_WRITE_MASK,
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+ access | PFERR_WRITE_MASK,
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exception);
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unsigned offset = addr & (PAGE_SIZE-1);
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unsigned towrite = min(bytes, (unsigned)PAGE_SIZE - offset);
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