[PATCH v4 18/75] x86/boot/compressed/64: Add stage1 #VC handler

Joerg Roedel
2020-07-14T12:16:45Z

From: Joerg Roedel <jroedel@suse.de>

Add the first handler for #VC exceptions. At stage 1 there is no GHCB
yet becaue the kernel might still be running on the EFI page table.

The stage 1 handler is limited to the MSR based protocol to talk to
the hypervisor and can only support CPUID exit-codes, but that is
enough to get to stage 2.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/boot/compressed/Makefile | 1 +
arch/x86/boot/compressed/idt_64.c | 4 ++
arch/x86/boot/compressed/idt_handlers_64.S | 4 ++
arch/x86/boot/compressed/misc.h | 1 +
arch/x86/boot/compressed/sev-es.c | 45 +++++++++++++++
arch/x86/include/asm/msr-index.h | 1 +
arch/x86/include/asm/sev-es.h | 37 ++++++++++++
arch/x86/include/asm/trapnr.h | 1 +
arch/x86/kernel/sev-es-shared.c | 66 ++++++++++++++++++++++
9 files changed, 160 insertions(+)
create mode 100644 arch/x86/boot/compressed/sev-es.c
create mode 100644 arch/x86/include/asm/sev-es.h
create mode 100644 arch/x86/kernel/sev-es-shared.c

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index c825c95d13b9..b66f393e5a87 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -87,6 +87,7 @@ ifdef CONFIG_X86_64
vmlinux-objs-y += $(obj)/idt_64.o $(obj)/idt_handlers_64.o
vmlinux-objs-y += $(obj)/mem_encrypt.o
vmlinux-objs-y += $(obj)/pgtable_64.o
+ vmlinux-objs-$(CONFIG_AMD_MEM_ENCRYPT) += $(obj)/sev-es.o
endif

vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
diff --git a/arch/x86/boot/compressed/idt_64.c b/arch/x86/boot/compressed/idt_64.c
index 5f083092a86d..f3ca7324be44 100644
--- a/arch/x86/boot/compressed/idt_64.c
+++ b/arch/x86/boot/compressed/idt_64.c
@@ -32,6 +32,10 @@ void load_stage1_idt(void)
{
boot_idt_desc.address = (unsigned long)boot_idt;

+
+ if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
+ set_idt_entry(X86_TRAP_VC, boot_stage1_vc);
+
load_boot_idt(&boot_idt_desc);
}

diff --git a/arch/x86/boot/compressed/idt_handlers_64.S b/arch/x86/boot/compressed/idt_handlers_64.S
index b20e57504a94..92eb4df478a1 100644
--- a/arch/x86/boot/compressed/idt_handlers_64.S
+++ b/arch/x86/boot/compressed/idt_handlers_64.S
@@ -70,3 +70,7 @@ SYM_FUNC_END(\name)
.code64

EXCEPTION_HANDLER boot_page_fault do_boot_page_fault error_code=1
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+EXCEPTION_HANDLER boot_stage1_vc do_vc_no_ghcb error_code=1
+#endif
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index ea6174bad699..65da40777bc1 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -141,5 +141,6 @@ extern struct desc_ptr boot_idt_desc;

/* IDT Entry Points */
void boot_page_fault(void);
+void boot_stage1_vc(void);

#endif /* BOOT_COMPRESSED_MISC_H */
diff --git a/arch/x86/boot/compressed/sev-es.c b/arch/x86/boot/compressed/sev-es.c
new file mode 100644
index 000000000000..bb91cbb5920e
--- /dev/null
+++ b/arch/x86/boot/compressed/sev-es.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * AMD Encrypted Register State Support
+ *
+ * Author: Joerg Roedel <jroedel@suse.de>
+ */
+
+/*
+ * misc.h needs to be first because it knows how to include the other kernel
+ * headers in the pre-decompression code in a way that does not break
+ * compilation.
+ */
+#include "misc.h"
+
+#include <asm/sev-es.h>
+#include <asm/msr-index.h>
+#include <asm/ptrace.h>
+#include <asm/svm.h>
+
+static inline u64 sev_es_rd_ghcb_msr(void)
+{
+ unsigned long low, high;
+
+ asm volatile("rdmsr\n" : "=a" (low), "=d" (high) :
+ "c" (MSR_AMD64_SEV_ES_GHCB));
+
+ return ((high << 32) | low);
+}
+
+static inline void sev_es_wr_ghcb_msr(u64 val)
+{
+ u32 low, high;
+
+ low = val & 0xffffffffUL;
+ high = val >> 32;
+
+ asm volatile("wrmsr\n" : : "c" (MSR_AMD64_SEV_ES_GHCB),
+ "a"(low), "d" (high) : "memory");
+}
+
+#undef __init
+#define __init
+
+/* Include code for early handlers */
+#include "../../kernel/sev-es-shared.c"
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index e8370e64a155..2816eb01463f 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -448,6 +448,7 @@
#define MSR_AMD64_IBSBRTARGET 0xc001103b
#define MSR_AMD64_IBSOPDATA4 0xc001103d
#define MSR_AMD64_IBS_REG_COUNT_MAX 8 /* includes MSR_AMD64_IBSBRTARGET */
+#define MSR_AMD64_SEV_ES_GHCB 0xc0010130
#define MSR_AMD64_SEV 0xc0010131
#define MSR_AMD64_SEV_ENABLED_BIT 0
#define MSR_AMD64_SEV_ENABLED BIT_ULL(MSR_AMD64_SEV_ENABLED_BIT)
diff --git a/arch/x86/include/asm/sev-es.h b/arch/x86/include/asm/sev-es.h
new file mode 100644
index 000000000000..5d49a8a429d3
--- /dev/null
+++ b/arch/x86/include/asm/sev-es.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * AMD Encrypted Register State Support
+ *
+ * Author: Joerg Roedel <jroedel@suse.de>
+ */
+
+#ifndef __ASM_ENCRYPTED_STATE_H
+#define __ASM_ENCRYPTED_STATE_H
+
+#include <linux/types.h>
+
+#define GHCB_SEV_CPUID_REQ 0x004UL
+#define GHCB_CPUID_REQ_EAX 0
+#define GHCB_CPUID_REQ_EBX 1
+#define GHCB_CPUID_REQ_ECX 2
+#define GHCB_CPUID_REQ_EDX 3
+#define GHCB_CPUID_REQ(fn, reg) (GHCB_SEV_CPUID_REQ | \
+ (((unsigned long)reg & 3) << 30) | \
+ (((unsigned long)fn) << 32))
+
+#define GHCB_SEV_CPUID_RESP 0x005UL
+#define GHCB_SEV_TERMINATE 0x100UL
+
+#define GHCB_SEV_GHCB_RESP_CODE(v) ((v) & 0xfff)
+#define VMGEXIT() { asm volatile("rep; vmmcall\n\r"); }
+
+void __init do_vc_no_ghcb(struct pt_regs *regs, unsigned long exit_code);
+
+static inline u64 lower_bits(u64 val, unsigned int bits)
+{
+ u64 mask = (1ULL << bits) - 1;
+
+ return (val & mask);
+}
+
+#endif
diff --git a/arch/x86/include/asm/trapnr.h b/arch/x86/include/asm/trapnr.h
index 082f45631fa9..f5d2325aa0b7 100644
--- a/arch/x86/include/asm/trapnr.h
+++ b/arch/x86/include/asm/trapnr.h
@@ -26,6 +26,7 @@
#define X86_TRAP_XF 19 /* SIMD Floating-Point Exception */
#define X86_TRAP_VE 20 /* Virtualization Exception */
#define X86_TRAP_CP 21 /* Control Protection Exception */
+#define X86_TRAP_VC 29 /* VMM Communication Exception */
#define X86_TRAP_IRET 32 /* IRET Exception */

#endif
diff --git a/arch/x86/kernel/sev-es-shared.c b/arch/x86/kernel/sev-es-shared.c
new file mode 100644
index 000000000000..0bea32341afa
--- /dev/null
+++ b/arch/x86/kernel/sev-es-shared.c
@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * AMD Encrypted Register State Support
+ *
+ * Author: Joerg Roedel <jroedel@suse.de>
+ *
+ * This file is not compiled stand-alone. It contains code shared
+ * between the pre-decompression boot code and the running Linux kernel
+ * and is included directly into both code-bases.
+ */
+
+/*
+ * Boot VC Handler - This is the first VC handler during boot, there is no GHCB
+ * page yet, so it only supports the MSR based communication with the
+ * hypervisor and only the CPUID exit-code.
+ */
+void __init do_vc_no_ghcb(struct pt_regs *regs, unsigned long exit_code)
+{
+ unsigned int fn = lower_bits(regs->ax, 32);
+ unsigned long val;
+
+ /* Only CPUID is supported via MSR protocol */
+ if (exit_code != SVM_EXIT_CPUID)
+ goto fail;
+
+ sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EAX));
+ VMGEXIT();
+ val = sev_es_rd_ghcb_msr();
+ if (GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SEV_CPUID_RESP)
+ goto fail;
+ regs->ax = val >> 32;
+
+ sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EBX));
+ VMGEXIT();
+ val = sev_es_rd_ghcb_msr();
+ if (GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SEV_CPUID_RESP)
+ goto fail;
+ regs->bx = val >> 32;
+
+ sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_ECX));
+ VMGEXIT();
+ val = sev_es_rd_ghcb_msr();
+ if (GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SEV_CPUID_RESP)
+ goto fail;
+ regs->cx = val >> 32;
+
+ sev_es_wr_ghcb_msr(GHCB_CPUID_REQ(fn, GHCB_CPUID_REQ_EDX));
+ VMGEXIT();
+ val = sev_es_rd_ghcb_msr();
+ if (GHCB_SEV_GHCB_RESP_CODE(val) != GHCB_SEV_CPUID_RESP)
+ goto fail;
+ regs->dx = val >> 32;
+
+ /* Skip over the CPUID two-byte opcode */
+ regs->ip += 2;
+
+ return;
+
+fail:
+ sev_es_wr_ghcb_msr(GHCB_SEV_TERMINATE);
+ VMGEXIT();
+
+ /* Shouldn't get here - if we do halt the machine */
+ while (true)
+ asm volatile("hlt\n");
+}
--
2.27.0