lkml.org 
[lkml]   [2020]   [Sep]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] KVM: x86: Add kvm_x86_ops hook to short circuit emulation
Date
Replace the existing kvm_x86_ops.need_emulation_on_page_fault() with a
more generic is_emulatable(), and unconditionally call the new function
in x86_emulate_instruction().

KVM will use the generic hook to support multiple security related
technologies that prevent emulation in one way or another. Similar to
the existing AMD #NPF case where emulation of the current instruction is
not possible due to lack of information, AMD's SEV-ES and Intel's SGX
and TDX will introduce scenarios where emulation is impossible due to
the guest's register state being inaccessible. And again similar to the
existing #NPF case, emulation can be initiated by kvm_mmu_page_fault(),
i.e. outside of the control of vendor-specific code.

While the cause and architecturally visible behavior of the various
cases are different, e.g. SGX will inject a #UD, AMD #NPF is a clean
resume or complete shutdown, and SEV-ES and TDX "return" an error, the
impact on the common emulation code is identical: KVM must stop
emulation immediately and resume the guest.

Query is_emulatable() in handle_ud() as well so that the
force_emulation_prefix code doesn't incorrectly modify RIP before
calling emulate_instruction() in the absurdly unlikely scenario that
KVM encounters forced emulation in conjunction with "do not emulate".

Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/include/asm/kvm_host.h | 2 +-
arch/x86/kvm/mmu/mmu.c | 12 ------------
arch/x86/kvm/svm/svm.c | 31 ++++++++++++++++++-------------
arch/x86/kvm/vmx/vmx.c | 12 ++++++------
arch/x86/kvm/x86.c | 9 ++++++++-
5 files changed, 33 insertions(+), 33 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5303dbc5c9bc..fa89511ed9d6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1221,7 +1221,7 @@ struct kvm_x86_ops {

int (*get_msr_feature)(struct kvm_msr_entry *entry);

- bool (*need_emulation_on_page_fault)(struct kvm_vcpu *vcpu);
+ bool (*is_emulatable)(struct kvm_vcpu *vcpu, void *insn, int insn_len);

bool (*apic_init_signal_blocked)(struct kvm_vcpu *vcpu);
int (*enable_direct_tlbflush)(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index a5d0207e7189..f818a46db58c 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5485,18 +5485,6 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
if (!mmio_info_in_cache(vcpu, cr2_or_gpa, direct) && !is_guest_mode(vcpu))
emulation_type |= EMULTYPE_ALLOW_RETRY_PF;
emulate:
- /*
- * On AMD platforms, under certain conditions insn_len may be zero on #NPF.
- * This can happen if a guest gets a page-fault on data access but the HW
- * table walker is not able to read the instruction page (e.g instruction
- * page is not present in memory). In those cases we simply restart the
- * guest, with the exception of AMD Erratum 1096 which is unrecoverable.
- */
- if (unlikely(insn && !insn_len)) {
- if (!kvm_x86_ops.need_emulation_on_page_fault(vcpu))
- return 1;
- }
-
return x86_emulate_instruction(vcpu, cr2_or_gpa, emulation_type, insn,
insn_len);
}
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 03dd7bac8034..3a55495d985f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3933,19 +3933,10 @@ static void enable_smi_window(struct kvm_vcpu *vcpu)
}
}

-static bool svm_need_emulation_on_page_fault(struct kvm_vcpu *vcpu)
+static bool svm_is_emulatable(struct kvm_vcpu *vcpu, void *insn, int insn_len)
{
- unsigned long cr4 = kvm_read_cr4(vcpu);
- bool smep = cr4 & X86_CR4_SMEP;
- bool smap = cr4 & X86_CR4_SMAP;
- bool is_user = svm_get_cpl(vcpu) == 3;
-
- /*
- * If RIP is invalid, go ahead with emulation which will cause an
- * internal error exit.
- */
- if (!kvm_vcpu_gfn_to_memslot(vcpu, kvm_rip_read(vcpu) >> PAGE_SHIFT))
- return true;
+ bool smep, smap, is_user;
+ unsigned long cr4;

/*
* Detect and workaround Errata 1096 Fam_17h_00_0Fh.
@@ -3987,6 +3978,20 @@ static bool svm_need_emulation_on_page_fault(struct kvm_vcpu *vcpu)
* instruction pointer so we will not able to workaround it. Lets
* print the error and request to kill the guest.
*/
+ if (likely(!insn || insn_len))
+ return true;
+
+ /*
+ * If RIP is invalid, go ahead with emulation which will cause an
+ * internal error exit.
+ */
+ if (!kvm_vcpu_gfn_to_memslot(vcpu, kvm_rip_read(vcpu) >> PAGE_SHIFT))
+ return true;
+
+ cr4 = kvm_read_cr4(vcpu);
+ smep = cr4 & X86_CR4_SMEP;
+ smap = cr4 & X86_CR4_SMAP;
+ is_user = svm_get_cpl(vcpu) == 3;
if (smap && (!smep || is_user)) {
if (!sev_guest(vcpu->kvm))
return true;
@@ -4148,7 +4153,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
.mem_enc_reg_region = svm_register_enc_region,
.mem_enc_unreg_region = svm_unregister_enc_region,

- .need_emulation_on_page_fault = svm_need_emulation_on_page_fault,
+ .is_emulatable = svm_is_emulatable,

.apic_init_signal_blocked = svm_apic_init_signal_blocked,
};
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 46ba2e03a892..c92717c54bf9 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1561,6 +1561,11 @@ static int vmx_rtit_ctl_check(struct kvm_vcpu *vcpu, u64 data)
return 0;
}

+static bool vmx_is_emulatable(struct kvm_vcpu *vcpu, void *insn, int insn_len)
+{
+ return true;
+}
+
static int skip_emulated_instruction(struct kvm_vcpu *vcpu)
{
unsigned long rip, orig_rip;
@@ -7843,11 +7848,6 @@ static void enable_smi_window(struct kvm_vcpu *vcpu)
/* RSM will cause a vmexit anyway. */
}

-static bool vmx_need_emulation_on_page_fault(struct kvm_vcpu *vcpu)
-{
- return false;
-}
-
static bool vmx_apic_init_signal_blocked(struct kvm_vcpu *vcpu)
{
return to_vmx(vcpu)->nested.vmxon;
@@ -8002,7 +8002,7 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
.pre_leave_smm = vmx_pre_leave_smm,
.enable_smi_window = enable_smi_window,

- .need_emulation_on_page_fault = vmx_need_emulation_on_page_fault,
+ .is_emulatable = vmx_is_emulatable,
.apic_init_signal_blocked = vmx_apic_init_signal_blocked,
.migrate_timers = vmx_migrate_timers,
};
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 539ea1cd6020..5208217049d9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5707,6 +5707,9 @@ int handle_ud(struct kvm_vcpu *vcpu)
char sig[5]; /* ud2; .ascii "kvm" */
struct x86_exception e;

+ if (unlikely(!kvm_x86_ops.is_emulatable(vcpu, NULL, 0)))
+ return 1;
+
if (force_emulation_prefix &&
kvm_read_guest_virt(vcpu, kvm_get_linear_rip(vcpu),
sig, sizeof(sig), &e) == 0 &&
@@ -6912,7 +6915,10 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
int r;
struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
bool writeback = true;
- bool write_fault_to_spt = vcpu->arch.write_fault_to_shadow_pgtable;
+ bool write_fault_to_spt;
+
+ if (unlikely(!kvm_x86_ops.is_emulatable(vcpu, insn, insn_len)))
+ return 1;

vcpu->arch.l1tf_flush_l1d = true;

@@ -6920,6 +6926,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
* Clear write_fault_to_shadow_pgtable here to ensure it is
* never reused.
*/
+ write_fault_to_spt = vcpu->arch.write_fault_to_shadow_pgtable;
vcpu->arch.write_fault_to_shadow_pgtable = false;
kvm_clear_exception_queue(vcpu);

--
2.28.0
\
 
 \ /
  Last update: 2020-09-16 01:28    [W:0.074 / U:7.756 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site