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SubjectRe: [PATCH RFC 02/39] KVM: x86/xen: intercept xen hypercalls if enabled
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On Tue, 2020-12-01 at 09:48 +0000, David Woodhouse wrote:
> So I switched it to generate the hypercall page directly from the
> kernel, just like we do for the Hyper-V hypercall page.

Speaking of Hyper-V... I'll post this one now so you can start heckling
it.

I won't post the rest as I go; not much of the rest of the series when
I eventually post it will be very new and exciting. It'll just be
rebasing and tweaking your originals and perhaps adding some tests.

=======================
From db020c521c3a96b698a78d4e62cdd19da3831585 Mon Sep 17 00:00:00 2001
From: David Woodhouse <dwmw@amazon.co.uk>
Date: Tue, 1 Dec 2020 10:59:26 +0000
Subject: [PATCH] KVM: x86: Fix coexistence of Xen and Hyper-V hypercalls

Disambiguate Xen vs. Hyper-V calls by adding 'orl $0x80000000, %eax'
at the start of the Hyper-V hypercall page when Xen hypercalls are
also enabled.

That bit is reserved in the Hyper-V ABI, and those hypercall numbers
will never be used by Xen (because it does precisely the same trick).

Switch to using kvm_vcpu_write_guest() while we're at it, instead of
open-coding it.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
arch/x86/kvm/hyperv.c | 40 ++++++++++++++-----
arch/x86/kvm/xen.c | 6 +++
.../selftests/kvm/x86_64/xen_vmcall_test.c | 39 +++++++++++++++---
3 files changed, 68 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 5c7c4060b45c..347ff9ad70b3 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -23,6 +23,7 @@
#include "ioapic.h"
#include "cpuid.h"
#include "hyperv.h"
+#include "xen.h"

#include <linux/cpu.h>
#include <linux/kvm_host.h>
@@ -1139,9 +1140,9 @@ static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data,
hv->hv_hypercall &= ~HV_X64_MSR_HYPERCALL_ENABLE;
break;
case HV_X64_MSR_HYPERCALL: {
- u64 gfn;
- unsigned long addr;
- u8 instructions[4];
+ u8 instructions[9];
+ int i = 0;
+ u64 addr;

/* if guest os id is not set hypercall should remain disabled */
if (!hv->hv_guest_os_id)
@@ -1150,16 +1151,33 @@ static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data,
hv->hv_hypercall = data;
break;
}
- gfn = data >> HV_X64_MSR_HYPERCALL_PAGE_ADDRESS_SHIFT;
- addr = gfn_to_hva(kvm, gfn);
- if (kvm_is_error_hva(addr))
- return 1;
- kvm_x86_ops.patch_hypercall(vcpu, instructions);
- ((unsigned char *)instructions)[3] = 0xc3; /* ret */
- if (__copy_to_user((void __user *)addr, instructions, 4))
+
+ /*
+ * If Xen and Hyper-V hypercalls are both enabled, disambiguate
+ * the same way Xen itself does, by setting the bit 31 of EAX
+ * which is RsvdZ in the 32-bit Hyper-V hypercall ABI and just
+ * going to be clobbered on 64-bit.
+ */
+ if (kvm_xen_hypercall_enabled(kvm)) {
+ /* orl $0x80000000, %eax */
+ instructions[i++] = 0x0d;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0x80;
+ }
+
+ /* vmcall/vmmcall */
+ kvm_x86_ops.patch_hypercall(vcpu, instructions + i);
+ i += 3;
+
+ /* ret */
+ ((unsigned char *)instructions)[i++] = 0xc3;
+
+ addr = data & HV_X64_MSR_HYPERCALL_PAGE_ADDRESS_MASK;
+ if (kvm_vcpu_write_guest(vcpu, addr, instructions, i))
return 1;
hv->hv_hypercall = data;
- mark_page_dirty(kvm, gfn);
break;
}
case HV_X64_MSR_REFERENCE_TSC:
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 6400a4bc8480..c3426213a970 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -8,6 +8,7 @@

#include "x86.h"
#include "xen.h"
+#include "hyperv.h"

#include <linux/kvm_host.h>

@@ -99,6 +100,11 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu)

input = (u64)kvm_register_read(vcpu, VCPU_REGS_RAX);

+ /* Hyper-V hypercalls get bit 31 set in EAX */
+ if ((input & 0x80000000) &&
+ kvm_hv_hypercall_enabled(vcpu->kvm))
+ return kvm_hv_hypercall(vcpu);
+
longmode = is_64_bit_mode(vcpu);
if (!longmode) {
params[0] = (u32)kvm_rbx_read(vcpu);
diff --git a/tools/testing/selftests/kvm/x86_64/xen_vmcall_test.c
b/tools/testing/selftests/kvm/x86_64/xen_vmcall_test.c
index 3f1dd93626e5..24f279e1a66b 100644
--- a/tools/testing/selftests/kvm/x86_64/xen_vmcall_test.c
+++ b/tools/testing/selftests/kvm/x86_64/xen_vmcall_test.c
@@ -15,6 +15,7 @@

#define HCALL_REGION_GPA 0xc0000000ULL
#define HCALL_REGION_SLOT 10
+#define PAGE_SIZE 4096

static struct kvm_vm *vm;

@@ -22,7 +23,12 @@ static struct kvm_vm *vm;
#define ARGVALUE(x) (0xdeadbeef5a5a0000UL + x)
#define RETVALUE 0xcafef00dfbfbffffUL

-#define XEN_HYPERCALL_MSR 0x40000000
+#define XEN_HYPERCALL_MSR 0x40000200
+#define HV_GUEST_OS_ID_MSR 0x40000000
+#define HV_HYPERCALL_MSR 0x40000001
+
+#define HVCALL_SIGNAL_EVENT 0x005d
+#define HV_STATUS_INVALID_ALIGNMENT 4

static void guest_code(void)
{
@@ -30,6 +36,7 @@ static void guest_code(void)
unsigned long rdi = ARGVALUE(1);
unsigned long rsi = ARGVALUE(2);
unsigned long rdx = ARGVALUE(3);
+ unsigned long rcx;
register unsigned long r10 __asm__("r10") = ARGVALUE(4);
register unsigned long r8 __asm__("r8") = ARGVALUE(5);
register unsigned long r9 __asm__("r9") = ARGVALUE(6);
@@ -41,18 +48,38 @@ static void guest_code(void)
"r"(r10), "r"(r8), "r"(r9));
GUEST_ASSERT(rax == RETVALUE);

- /* Now fill in the hypercall page */
+ /* Fill in the Xen hypercall page */
__asm__ __volatile__("wrmsr" : : "c" (XEN_HYPERCALL_MSR),
"a" (HCALL_REGION_GPA & 0xffffffff),
"d" (HCALL_REGION_GPA >> 32));

- /* And invoke the same hypercall that way */
+ /* Set Hyper-V Guest OS ID */
+ __asm__ __volatile__("wrmsr" : : "c" (HV_GUEST_OS_ID_MSR),
+ "a" (0x5a), "d" (0));
+
+ /* Hyper-V hypercall page */
+ u64 msrval = HCALL_REGION_GPA + PAGE_SIZE + 1;
+ __asm__ __volatile__("wrmsr" : : "c" (HV_HYPERCALL_MSR),
+ "a" (msrval & 0xffffffff),
+ "d" (msrval >> 32));
+
+ /* Invoke a Xen hypercall */
__asm__ __volatile__("call *%1" : "=a"(rax) :
"r"(HCALL_REGION_GPA + INPUTVALUE * 32),
"a"(rax), "D"(rdi), "S"(rsi), "d"(rdx),
"r"(r10), "r"(r8), "r"(r9));
GUEST_ASSERT(rax == RETVALUE);

+ /* Invoke a Hyper-V hypercall */
+ rax = 0;
+ rcx = HVCALL_SIGNAL_EVENT; /* code */
+ rdx = 0x5a5a5a5a; /* ingpa (badly aligned) */
+ __asm__ __volatile__("call *%1" : "=a"(rax) :
+ "r"(HCALL_REGION_GPA + PAGE_SIZE),
+ "a"(rax), "c"(rcx), "d"(rdx),
+ "r"(r8));
+ GUEST_ASSERT(rax == HV_STATUS_INVALID_ALIGNMENT);
+
GUEST_DONE();
}

@@ -73,11 +100,11 @@ int main(int argc, char *argv[])
};
vm_ioctl(vm, KVM_XEN_HVM_CONFIG, &hvmc);

- /* Map a region for the hypercall page */
+ /* Map a region for the hypercall pages */
vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
HCALL_REGION_GPA,
HCALL_REGION_SLOT,
- getpagesize(), 0);
- virt_map(vm, HCALL_REGION_GPA, HCALL_REGION_GPA, 1, 0);
+ 2 * getpagesize(), 0);
+ virt_map(vm, HCALL_REGION_GPA, HCALL_REGION_GPA, 2, 0);

for (;;) {
volatile struct kvm_run *run = vcpu_state(vm, VCPU_ID);
--
2.17.1
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