[PATCH v6 42/76] x86/sev-es: Setup early #VC handler

Joerg Roedel
2020-08-24T09:08:08Z

From: Joerg Roedel <jroedel@suse.de>

Setup an early handler for #VC exceptions. There is no GHCB mapped
yet, so just re-use the vc_no_ghcb_handler. It can only handle CPUID
exit-codes, but that should be enough to get the kernel through
verify_cpu() and __startup_64() until it runs on virtual addresses.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Link: https://lore.kernel.org/r/20200724160336.5435-42-joro@8bytes.org
---
arch/x86/include/asm/setup.h | 1 +
arch/x86/include/asm/sev-es.h | 3 +++
arch/x86/kernel/head64.c | 1 +
arch/x86/kernel/head_64.S | 34 +++++++++++++++++++++++++++++++++
arch/x86/kernel/idt.c | 36 +++++++++++++++++++++++++++++++++++
5 files changed, 75 insertions(+)

diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
index cafae86813ae..0ce6453c9272 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -53,6 +53,7 @@ extern unsigned long __startup_secondary_64(void);
extern void startup_64_setup_env(unsigned long physbase);
extern void early_idt_setup_early_handler(unsigned long physaddr);
extern void early_load_idt(void);
+extern void early_idt_setup(unsigned long physbase);
extern void __init do_early_exception(struct pt_regs *regs, int trapnr);

#ifdef CONFIG_X86_INTEL_MID
diff --git a/arch/x86/include/asm/sev-es.h b/arch/x86/include/asm/sev-es.h
index 7c0807b84546..ec0e112a742b 100644
--- a/arch/x86/include/asm/sev-es.h
+++ b/arch/x86/include/asm/sev-es.h
@@ -73,4 +73,7 @@ static inline u64 lower_bits(u64 val, unsigned int bits)
return (val & mask);
}

+/* Early IDT entry points for #VC handler */
+extern void vc_no_ghcb(void);
+
#endif
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 41514ec1e6f0..250fae33bf66 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -39,6 +39,7 @@
#include <asm/realmode.h>
#include <asm/extable.h>
#include <asm/trapnr.h>
+#include <asm/sev-es.h>

/*
* Manage page tables very early on.
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 4622940134a5..12bf6f11fd83 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -95,6 +95,13 @@ SYM_CODE_START_NOALIGN(startup_64)
.Lon_kernel_cs:
UNWIND_HINT_EMPTY

+ /* Setup IDT - Needed for SEV-ES */
+ pushq %rsi
+ /* early_idt_setup - physbase as first parameter */
+ leaq _text(%rip), %rdi
+ call early_idt_setup
+ popq %rsi
+
/* Sanitize CPU configuration */
call verify_cpu

@@ -363,6 +370,33 @@ SYM_CODE_START_LOCAL(early_idt_handler_common)
jmp restore_regs_and_return_to_kernel
SYM_CODE_END(early_idt_handler_common)

+#ifdef CONFIG_AMD_MEM_ENCRYPT
+/*
+ * VC Exception handler used during very early boot. The
+ * early_idt_handler_array can't be used because it returns via the
+ * paravirtualized INTERRUPT_RETURN and pv-ops don't work that early.
+ */
+SYM_CODE_START_NOALIGN(vc_no_ghcb)
+ UNWIND_HINT_IRET_REGS offset=8
+
+ /* Build pt_regs */
+ PUSH_AND_CLEAR_REGS
+
+ /* Call C handler */
+ movq %rsp, %rdi
+ movq ORIG_RAX(%rsp), %rsi
+ call do_vc_no_ghcb
+
+ /* Unwind pt_regs */
+ POP_REGS
+
+ /* Remove Error Code */
+ addq $8, %rsp
+
+ /* Pure iret required here - don't use INTERRUPT_RETURN */
+ iretq
+SYM_CODE_END(vc_no_ghcb)
+#endif

#define SYM_DATA_START_PAGE_ALIGNED(name) \
SYM_START(name, SYM_L_GLOBAL, .balign PAGE_SIZE)
diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index e2777cc264f5..0d560a1218e1 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -11,6 +11,7 @@
#include <asm/desc.h>
#include <asm/hw_irq.h>
#include <asm/setup.h>
+#include <asm/sev-es.h>

struct idt_data {
unsigned int vector;
@@ -408,3 +409,38 @@ void early_load_idt(void)
{
load_idt(&idt_descr);
}
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+static void set_early_idt_handler(gate_desc *idt, int n, void *handler)
+{
+ struct idt_data data;
+ gate_desc desc;
+
+ init_idt_data(&data, n, handler);
+ idt_init_desc(&desc, &data);
+ native_write_idt_entry(idt, n, &desc);
+}
+#endif
+
+static struct desc_ptr early_idt_descr __initdata = {
+ .size = IDT_TABLE_SIZE - 1,
+ .address = 0 /* Needs physical address of idt_table - initialized at runtime. */,
+};
+
+void __init early_idt_setup(unsigned long physbase)
+{
+ void __maybe_unused *handler;
+ gate_desc *idt;
+
+ idt = fixup_pointer(idt_table, physbase);
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+ /* VMM Communication Exception */
+ handler = fixup_pointer(vc_no_ghcb, physbase);
+ set_early_idt_handler(idt, X86_TRAP_VC, handler);
+#endif
+
+ /* Initialize IDT descriptor and load IDT */
+ early_idt_descr.address = (unsigned long)idt;
+ native_load_idt(&early_idt_descr);
+}
--
2.28.0