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KVM: x86: Update emulator context mode if SYSENTER xfers to 64-bit mode

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Set the emulator context to PROT64 if SYSENTER transitions from 32-bit
userspace (compat mode) to a 64-bit kernel, otherwise the RIP update at
the end of x86_emulate_insn() will incorrectly truncate the new RIP.

Note, this bug is mostly limited to running an Intel virtual CPU model on
an AMD physical CPU, as other combinations of virtual and physical CPUs
do not trigger full emulation.  On Intel CPUs, SYSENTER in compatibility
mode is legal, and unconditionally transitions to 64-bit mode.  On AMD
CPUs, SYSENTER is illegal in compatibility mode and #UDs.  If the vCPU is
AMD, KVM injects a #UD on SYSENTER in compat mode.  If the pCPU is Intel,
SYSENTER will execute natively and not trigger #UD->VM-Exit (ignoring
guest TLB shenanigans).

Fixes: fede8076aa ("KVM: x86: handle wrap around 32-bit address space")
Cc: stable@vger.kernel.org
Signed-off-by: Jonny Barker <jonny@jonnybarker.com>
[sean: wrote changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210202165546.2390296-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-02-02 08:55:46 -08:00 committed by Paolo Bonzini
parent 4683d758f4
commit 943dea8af2
1 changed files with 2 additions and 0 deletions
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2
arch/x86/kvm/emulate.c
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@ -2879,6 +2879,8 @@ static int em_sysenter(struct x86_emulate_ctxt *ctxt)
ops->get_msr(ctxt, MSR_IA32_SYSENTER_ESP, &msr_data);
*reg_write(ctxt, VCPU_REGS_RSP) = (efer & EFER_LMA) ? msr_data :
(u32)msr_data;
if (efer & EFER_LMA)
ctxt->mode = X86EMUL_MODE_PROT64;
return X86EMUL_CONTINUE;
}