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From 848115120ffa7b2287069fe6d23683304b9ffec1 Mon Sep 17 00:00:00 2001
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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Fri, 12 Sep 2014 11:56:31 +0200
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Subject: [PATCH 31/43] target-i386: get CPL from SS.DPL
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Message-id: <1410522991-11612-2-git-send-email-pbonzini@redhat.com>
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Patchwork-id: 61022
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O-Subject: [RHEL 7.1 qemu-kvm PATCH] target-i386: get CPL from SS.DPL
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Bugzilla: 1097363
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RH-Acked-by: wei@redhat.com
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RH-Acked-by: Radim Krcmar <rkrcmar@redhat.com>
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RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
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CS.RPL is not equal to the CPL in the few instructions between
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setting CR0.PE and reloading CS. We get this right in the common
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case, because writes to CR0 do not modify the CPL, but it would
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not be enough if an SMI comes exactly during that brief period.
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Were this to happen, the RSM instruction would erroneously set
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CPL to the low two bits of the real-mode selector; and if they are
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not 00, the next instruction fetch cannot access the code segment
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and causes a triple fault.
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However, SS.DPL *is* always equal to the CPL. In real processors
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(AMD only) there is a weird case of SYSRET setting SS.DPL=SS.RPL
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from the STAR register while forcing CPL=3, but we do not emulate
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that.
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Tested-by: Kevin O'Connor <kevin@koconnor.net>
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Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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(cherry picked from commit 7125c937c97d9ec4a41b3cb6d1b3e805ec53e255)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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Conflicts:
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target-i386/cpu.h [only needed for TCG and has other dependencies]
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---
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target-i386/kvm.c | 2 +-
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target-i386/machine.c | 8 ++++++++
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2 files changed, 9 insertions(+), 1 deletion(-)
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diff --git a/target-i386/kvm.c b/target-i386/kvm.c
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index 6b250f5..65362ac 100644
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--- a/target-i386/kvm.c
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+++ b/target-i386/kvm.c
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@@ -1381,7 +1381,7 @@ static int kvm_get_sregs(X86CPU *cpu)
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HF_OSFXSR_MASK | HF_LMA_MASK | HF_CS32_MASK | \
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HF_SS32_MASK | HF_CS64_MASK | HF_ADDSEG_MASK)
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- hflags = (env->segs[R_CS].flags >> DESC_DPL_SHIFT) & HF_CPL_MASK;
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+ hflags = (env->segs[R_SS].flags >> DESC_DPL_SHIFT) & HF_CPL_MASK;
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hflags |= (env->cr[0] & CR0_PE_MASK) << (HF_PE_SHIFT - CR0_PE_SHIFT);
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hflags |= (env->cr[0] << (HF_MP_SHIFT - CR0_MP_SHIFT)) &
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(HF_MP_MASK | HF_EM_MASK | HF_TS_MASK);
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diff --git a/target-i386/machine.c b/target-i386/machine.c
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index 42b049b..87fd496 100644
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--- a/target-i386/machine.c
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+++ b/target-i386/machine.c
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@@ -296,6 +296,14 @@ static int cpu_post_load(void *opaque, int version_id)
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env->segs[R_SS].flags &= ~(env->segs[R_SS].flags & DESC_DPL_MASK);
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}
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+ /* Older versions of QEMU incorrectly used CS.DPL as the CPL when
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+ * running under KVM. This is wrong for conforming code segments.
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+ * Luckily, in our implementation the CPL field of hflags is redundant
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+ * and we can get the right value from the SS descriptor privilege level.
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+ */
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+ env->hflags &= ~HF_CPL_MASK;
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+ env->hflags |= (env->segs[R_SS].flags >> DESC_DPL_SHIFT) & HF_CPL_MASK;
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+
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/* XXX: restore FPU round state */
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env->fpstt = (env->fpus_vmstate >> 11) & 7;
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env->fpus = env->fpus_vmstate & ~0x3800;
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--
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1.8.3.1
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