AMD SEV-ES defines a new guest exception that gets triggered on
some vmexits to allow the guest to control what state gets shared
with the host. kvm-unit-tests currently relies on UEFI to provide
this #VC exception handler. This leads to the following problems:
1) The test's page table needs to map the firmware and the shared
GHCB used by the firmware.
2) The firmware needs to keep its #VC handler in the current IDT
so that kvm-unit-tests can copy the #VC entry into its own IDT.
3) The firmware #VC handler might use state which is not available
anymore after ExitBootServices.
4) After ExitBootServices, the firmware needs to get the GHCB address
from the GHCB MSR if it needs to use the kvm-unit-test GHCB. This
requires keeping an identity mapping, and the GHCB address must be
in the MSR at all times where a #VC could happen.
Problems 1) and 2) were temporarily mitigated via commits b114aa57ab
("x86 AMD SEV-ES: Set up GHCB page") and 706ede1833 ("x86 AMD SEV-ES:
Copy UEFI #VC IDT entry") respectively.
However, to make kvm-unit-tests reliable against 3) and 4), the tests
must supply their own #VC handler [1][2].
Switch the tests to install a #VC handler on early bootup, just after
GHCB has been mapped. The tests will use this handler by default.
If --amdsev-efi-vc is passed during ./configure, the tests will
continue using the UEFI #VC handler.
[1] https://lore.kernel.org/all/Yf0GO8EydyQSdZvu@xxxxxxx/
[2] https://lore.kernel.org/all/YSA%2FsYhGgMU72tn+@xxxxxxxxxx/
Signed-off-by: Varad Gautam <varad.gautam@xxxxxxxx>
Signed-off-by: Vasant Karasulli <vkarasulli@xxxxxxx>
Reviewed-by: Marc Orr <marcorr@xxxxxxxxxx>
---
Makefile | 3 +++
configure | 21 +++++++++++++++++++++
lib/x86/amd_sev.c | 13 +++++--------
lib/x86/amd_sev.h | 1 +
lib/x86/amd_sev_vc.c | 15 +++++++++++++++
lib/x86/desc.c | 17 +++++++++++++++++
lib/x86/desc.h | 1 +
lib/x86/setup.c | 8 ++++++++
x86/Makefile.common | 1 +
9 files changed, 72 insertions(+), 8 deletions(-)
create mode 100644 lib/x86/amd_sev_vc.c
diff --git a/Makefile b/Makefile
index 8809a8b..3ad06f0 100644
--- a/Makefile
+++ b/Makefile
@@ -41,6 +41,9 @@ OBJDIRS += $(LIBFDT_objdir)
# EFI App
ifeq ($(CONFIG_EFI),y)
EFI_CFLAGS := -DCONFIG_EFI -DCONFIG_RELOC
+ifeq ($(AMDSEV_EFI_VC),y)
+EFI_CFLAGS += -DAMDSEV_EFI_VC
+endif
# The following CFLAGS and LDFLAGS come from:
# - GNU-EFI/Makefile.defaults
# - GNU-EFI/apps/Makefile
diff --git a/configure b/configure
index 6ee9b27..f39ecb0 100755
--- a/configure
+++ b/configure
@@ -32,6 +32,12 @@ enable_dump=no
page_size=
earlycon=
efi=
+# For AMD SEV-ES, the tests build to use their own #VC exception handler
+# by default, instead of using the one installed by UEFI. This ensures
+# that the tests do not depend on UEFI state after ExitBootServices.
+# To continue using the UEFI #VC handler, ./configure can be run with
+# --amdsev-efi-vc.
+amdsev_efi_vc=
# Enable -Werror by default for git repositories only (i.e. developer builds)
if [ -e "$srcdir"/.git ]; then
@@ -89,6 +95,8 @@ usage() {
--[enable|disable]-efi Boot and run from UEFI (disabled by default, x86_64 and arm64 only)
--[enable|disable]-werror
Select whether to compile with the -Werror compiler flag
+ --amdsev-efi-vc Use UEFI-provided #VC handlers on AMD SEV/ES. Requires
+ --enable-efi.
EOF
exit 1
}
@@ -174,6 +182,9 @@ while [[ "$1" = -* ]]; do
--disable-werror)
werror=
;;
+ --amdsev-efi-vc)
+ amdsev_efi_vc=y
+ ;;
--help)
usage
;;
@@ -249,8 +260,17 @@ elif [ "$processor" = "arm" ]; then
processor="cortex-a15"
fi
+if [ "$amdsev_efi_vc" ] && [ "$arch" != "x86_64" ]; then
+ echo "--amdsev-efi-vc requires arch x86_64."
+ usage
+fi
+
if [ "$arch" = "i386" ] || [ "$arch" = "x86_64" ]; then
testdir=x86
+ if [ "$amdsev_efi_vc" ] && [ -z "$efi" ]; then
+ echo "--amdsev-efi-vc requires --enable-efi."
+ usage
+ fi
elif [ "$arch" = "arm" ] || [ "$arch" = "arm64" ]; then
testdir=arm
if [ "$target" = "qemu" ]; then
@@ -413,6 +433,7 @@ GENPROTIMG=${GENPROTIMG-genprotimg}
HOST_KEY_DOCUMENT=$host_key_document
CONFIG_DUMP=$enable_dump
CONFIG_EFI=$efi
+AMDSEV_EFI_VC=$amdsev_efi_vc
CONFIG_WERROR=$werror
GEN_SE_HEADER=$gen_se_header
EOF
diff --git a/lib/x86/amd_sev.c b/lib/x86/amd_sev.c
index 6672214..987b59f 100644
--- a/lib/x86/amd_sev.c
+++ b/lib/x86/amd_sev.c
@@ -14,6 +14,7 @@
#include "x86/vm.h"
static unsigned short amd_sev_c_bit_pos;
+phys_addr_t ghcb_addr;
bool amd_sev_enabled(void)
{
@@ -100,14 +101,10 @@ efi_status_t setup_amd_sev_es(void)
/*
* Copy UEFI's #VC IDT entry, so KVM-Unit-Tests can reuse it and does
- * not have to re-implement a #VC handler. Also update the #VC IDT code
- * segment to use KVM-Unit-Tests segments, KERNEL_CS, so that we do not
+ * not have to re-implement a #VC handler for #VC exceptions before
+ * GHCB is mapped. Also update the #VC IDT code segment to use
+ * KVM-Unit-Tests segments, KERNEL_CS, so that we do not
* have to copy the UEFI GDT entries into KVM-Unit-Tests GDT.
- *
- * TODO: Reusing UEFI #VC handler is a temporary workaround to simplify
- * the boot up process, the long-term solution is to implement a #VC
- * handler in kvm-unit-tests and load it, so that kvm-unit-tests does
- * not depend on specific UEFI #VC handler implementation.
*/
sidt(&idtr);
idt = (idt_entry_t *)idtr.base;
@@ -126,7 +123,7 @@ void setup_ghcb_pte(pgd_t *page_table)
* function searches GHCB's L1 pte, creates corresponding L1 ptes if not
* found, and unsets the c-bit of GHCB's L1 pte.
*/
- phys_addr_t ghcb_addr, ghcb_base_addr;
+ phys_addr_t ghcb_base_addr;
pteval_t *pte;
/* Read the current GHCB page addr */
diff --git a/lib/x86/amd_sev.h b/lib/x86/amd_sev.h
index ed6e338..713019c 100644
--- a/lib/x86/amd_sev.h
+++ b/lib/x86/amd_sev.h
@@ -54,6 +54,7 @@ efi_status_t setup_amd_sev(void);
bool amd_sev_es_enabled(void);
efi_status_t setup_amd_sev_es(void);
void setup_ghcb_pte(pgd_t *page_table);
+void handle_sev_es_vc(struct ex_regs *regs);
unsigned long long get_amd_sev_c_bit_mask(void);
unsigned long long get_amd_sev_addr_upperbound(void);
diff --git a/lib/x86/amd_sev_vc.c b/lib/x86/amd_sev_vc.c
new file mode 100644
index 0000000..f622703
--- /dev/null
+++ b/lib/x86/amd_sev_vc.c
@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "amd_sev.h"
+
+extern phys_addr_t ghcb_addr;
+
+void handle_sev_es_vc(struct ex_regs *regs)
+{
+ struct ghcb *ghcb = (struct ghcb *) ghcb_addr;
+
+ if (!ghcb) {
+ /* TODO: kill guest */
+ return;
+ }
+}
diff --git a/lib/x86/desc.c b/lib/x86/desc.c
index b293ae4..dc8b901 100644
--- a/lib/x86/desc.c
+++ b/lib/x86/desc.c
@@ -4,6 +4,9 @@
#include "smp.h"
#include <setjmp.h>
#include "apic-defs.h"
+#ifdef CONFIG_EFI
+#include "amd_sev.h"
+#endif
/* Boot-related data structures */
@@ -243,6 +246,9 @@ EX_E(ac, 17);
EX(mc, 18);
EX(xm, 19);
EX_E(cp, 21);
+#ifdef CONFIG_EFI
+EX_E(vc, 29);
+#endif
asm (".pushsection .text \n\t"
"__handle_exception: \n\t"
@@ -309,6 +315,17 @@ void setup_idt(void)
}
}
+#ifdef CONFIG_EFI
+void setup_amd_sev_es_vc(void)
+{
+ if (!amd_sev_es_enabled())
+ return;
+
+ set_idt_entry(29, &vc_fault, 0);
+ handle_exception(29, handle_sev_es_vc);
+}
+#endif
+
void load_idt(void)
{
lidt(&idt_descr);
diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index c023b93..c6505aa 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -252,6 +252,7 @@ void print_current_tss_info(void);
handler handle_exception(u8 v, handler fn);
void unhandled_exception(struct ex_regs *regs, bool cpu);
const char* exception_mnemonic(int vector);
+void setup_amd_sev_es_vc(void);
bool test_for_exception(unsigned int ex, void (*trigger_func)(void *data),
void *data);
diff --git a/lib/x86/setup.c b/lib/x86/setup.c
index d509a24..65f5972 100644
--- a/lib/x86/setup.c
+++ b/lib/x86/setup.c
@@ -363,6 +363,14 @@ efi_status_t setup_efi(efi_bootinfo_t *efi_bootinfo)
save_id();
bsp_rest_init();
+#ifndef AMDSEV_EFI_VC
+ /*
+ * Switch away from the UEFI-installed #VC handler.
+ * GHCB has already been mapped at this point.
+ */
+ setup_amd_sev_es_vc();
+#endif /* AMDSEV_EFI_VC */
+
return EFI_SUCCESS;
}
diff --git a/x86/Makefile.common b/x86/Makefile.common
index 4ae9a55..bc0ed2c 100644
--- a/x86/Makefile.common
+++ b/x86/Makefile.common
@@ -25,6 +25,7 @@ cflatobjs += lib/x86/delay.o
cflatobjs += lib/x86/pmu.o
ifeq ($(CONFIG_EFI),y)
cflatobjs += lib/x86/amd_sev.o
+cflatobjs += lib/x86/amd_sev_vc.o
cflatobjs += lib/efi.o
cflatobjs += x86/efi/reloc_x86_64.o
endif
--
2.34.1
