[PATCH v3 41/75] x86/sev-es: Setup early #VC handler

Joerg Roedel
2020-04-28T15:22:04Z

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>
---
arch/x86/include/asm/desc.h | 1 +
arch/x86/include/asm/processor.h | 1 +
arch/x86/include/asm/sev-es.h | 2 ++
arch/x86/kernel/head64.c | 17 +++++++++++++++
arch/x86/kernel/head_64.S | 36 ++++++++++++++++++++++++++++++++
arch/x86/kernel/idt.c | 10 +++++++++
6 files changed, 67 insertions(+)

diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index 80bf63c08007..30e2a0e863b6 100644
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -388,6 +388,7 @@ static inline void set_desc_limit(struct desc_struct *desc, unsigned long limit)

void update_intr_gate(unsigned int n, const void *addr);
void alloc_intr_gate(unsigned int n, const void *addr);
+void set_early_idt_handler(gate_desc *idt, int n, void *handler);

static inline void init_idt_data(struct idt_data *data, unsigned int n,
const void *addr)
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 3bcf27caf6c9..e369271bfd33 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -757,6 +757,7 @@ extern int sysenter_setup(void);

/* Defined in head.S */
extern struct desc_ptr early_gdt_descr;
+extern struct desc_ptr early_idt_descr;

extern void switch_to_new_gdt(int);
extern void load_direct_gdt(int);
diff --git a/arch/x86/include/asm/sev-es.h b/arch/x86/include/asm/sev-es.h
index 7c0807b84546..b2cbcd40b52e 100644
--- a/arch/x86/include/asm/sev-es.h
+++ b/arch/x86/include/asm/sev-es.h
@@ -73,4 +73,6 @@ static inline u64 lower_bits(u64 val, unsigned int bits)
return (val & mask);
}

+extern void vc_no_ghcb(void);
+
#endif
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 474f121d50f6..9586522bfcb3 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -38,6 +38,7 @@
#include <asm/fixmap.h>
#include <asm/extable.h>
#include <asm/trap_defs.h>
+#include <asm/sev-es.h>

/*
* Manage page tables very early on.
@@ -515,3 +516,19 @@ void __head early_idt_setup_early_handler(unsigned long physaddr)
native_write_idt_entry(idt, i, &desc);
}
}
+
+void __head early_idt_setup(unsigned long physbase)
+{
+ gate_desc *idt = fixup_pointer(idt_table, physbase);
+ void __maybe_unused *handler;
+
+#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);
+}
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index aca3beb336ce..4d84a0c72e36 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -92,6 +92,12 @@ SYM_CODE_START_NOALIGN(startup_64)
.Lon_kernel_cs:
UNWIND_HINT_EMPTY

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

@@ -370,6 +376,33 @@ 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)
@@ -511,6 +544,9 @@ SYM_DATA_END(level1_fixmap_pgt)
SYM_DATA(early_gdt_descr, .word GDT_ENTRIES*8-1)
SYM_DATA_LOCAL(early_gdt_descr_base, .quad INIT_PER_CPU_VAR(gdt_page))

+SYM_DATA(early_idt_descr, .word NUM_EXCEPTION_VECTORS * 16)
+SYM_DATA_LOCAL(early_idt_descr_base, .quad 0)
+
.align 16
/* This must match the first entry in level2_kernel_pgt */
SYM_DATA(phys_base, .quad 0x0)
diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index 4a2c7791c697..135d208a2d38 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -341,3 +341,13 @@ void alloc_intr_gate(unsigned int n, const void *addr)
if (!test_and_set_bit(n, system_vectors))
set_intr_gate(n, addr);
}
+
+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);
+}
--
2.17.1