[PATCH v3 47/75] x86/sev-es: Add Runtime #VC Exception Handler

Joerg Roedel
2020-04-28T15:21:20Z

From: Tom Lendacky <thomas.lendacky@amd.com>

Add the handler for #VC exceptions invoked at runtime.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/entry/entry_64.S | 4 +
arch/x86/include/asm/traps.h | 7 ++
arch/x86/kernel/idt.c | 4 +-
arch/x86/kernel/sev-es.c | 167 ++++++++++++++++++++++++++++++++++-
4 files changed, 180 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 0e9504fabe52..4c392eb2f063 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1210,6 +1210,10 @@ idtentry async_page_fault do_async_page_fault has_error_code=1 read_cr2=1
idtentry machine_check do_mce has_error_code=0 paranoid=1
#endif

+#ifdef CONFIG_AMD_MEM_ENCRYPT
+idtentry vmm_communication do_vmm_communication has_error_code=1 paranoid=1 shift_ist=IST_INDEX_VC ist_offset=VC_STACK_OFFSET
+#endif
+
/*
* Save all registers in pt_regs, and switch gs if needed.
* Use slow, but surefire "are we in kernel?" check.
diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index 104991c05425..37f6e86ac53a 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -35,6 +35,9 @@ asmlinkage void alignment_check(void);
#ifdef CONFIG_X86_MCE
asmlinkage void machine_check(void);
#endif /* CONFIG_X86_MCE */
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+asmlinkage void vmm_communication(void);
+#endif
asmlinkage void simd_coprocessor_error(void);

#if defined(CONFIG_X86_64) && defined(CONFIG_XEN_PV)
@@ -83,6 +86,10 @@ dotraplinkage void do_spurious_interrupt_bug(struct pt_regs *regs, long error_co
dotraplinkage void do_coprocessor_error(struct pt_regs *regs, long error_code);
dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code);
dotraplinkage void do_simd_coprocessor_error(struct pt_regs *regs, long error_code);
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+dotraplinkage void do_vmm_communication_error(struct pt_regs *regs,
+ long error_code);
+#endif
#ifdef CONFIG_X86_32
dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code);
#endif
diff --git a/arch/x86/kernel/idt.c b/arch/x86/kernel/idt.c
index 135d208a2d38..e32cc5f3fa94 100644
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -88,7 +88,6 @@ static const __initconst struct idt_data def_idts[] = {
#ifdef CONFIG_X86_MCE
INTG(X86_TRAP_MC, &machine_check),
#endif
-
SYSG(X86_TRAP_OF, overflow),
#if defined(CONFIG_IA32_EMULATION)
SYSG(IA32_SYSCALL_VECTOR, entry_INT80_compat),
@@ -185,6 +184,9 @@ static const __initconst struct idt_data ist_idts[] = {
#ifdef CONFIG_X86_MCE
ISTG(X86_TRAP_MC, &machine_check, IST_INDEX_MCE),
#endif
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+ ISTG(X86_TRAP_VC, vmm_communication, IST_INDEX_VC),
+#endif
};

/*
diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index a4fa7f351bf2..bc3a58427028 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -10,6 +10,7 @@
#include <linux/sched/debug.h> /* For show_regs() */
#include <linux/percpu-defs.h>
#include <linux/mem_encrypt.h>
+#include <linux/lockdep.h>
#include <linux/printk.h>
#include <linux/mm_types.h>
#include <linux/set_memory.h>
@@ -25,7 +26,7 @@
#include <asm/insn-eval.h>
#include <asm/fpu/internal.h>
#include <asm/processor.h>
-#include <asm/trap_defs.h>
+#include <asm/traps.h>
#include <asm/svm.h>

/* For early boot hypervisor communication in SEV-ES enabled guests */
@@ -46,10 +47,26 @@ struct sev_es_runtime_data {

/* Physical storage for the per-cpu IST stacks of the #VC handler */
struct vmm_exception_stacks vc_stacks __aligned(PAGE_SIZE);
+
+ /* Reserve on page per CPU as backup storage for the unencrypted GHCB */
+ struct ghcb backup_ghcb;
+
+ /*
+ * Mark the per-cpu GHCBs as in-use to detect nested #VC exceptions.
+ * There is no need for it to be atomic, because nothing is written to
+ * the GHCB between the read and the write of ghcb_active. So it is safe
+ * to use it when a nested #VC exception happens before the write.
+ */
+ bool ghcb_active;
+ bool backup_ghcb_active;
};

static DEFINE_PER_CPU(struct sev_es_runtime_data*, runtime_data);

+struct ghcb_state {
+ struct ghcb *ghcb;
+};
+
/*
* Shift/Unshift the IST entry for the #VC handler during
* nmi_enter()/nmi_exit(). This is needed when an NMI hits in the #VC handlers
@@ -70,6 +87,53 @@ void sev_es_nmi_exit(void)
tss->x86_tss.ist[IST_INDEX_VC] += VC_STACK_OFFSET;
}

+static struct ghcb *sev_es_get_ghcb(struct ghcb_state *state)
+{
+ struct sev_es_runtime_data *data;
+ struct ghcb *ghcb;
+
+ data = this_cpu_read(runtime_data);
+ ghcb = &data->ghcb_page;
+
+ if (unlikely(data->ghcb_active)) {
+ /* GHCB is already in use - save its contents */
+
+ if (unlikely(data->backup_ghcb_active))
+ return NULL;
+
+ /* Mark backup_ghcb active before writing to it */
+ data->backup_ghcb_active = true;
+
+ state->ghcb = &data->backup_ghcb;
+
+ /* Backup GHCB content */
+ *state->ghcb = *ghcb;
+ } else {
+ state->ghcb = NULL;
+ data->ghcb_active = true;
+ }
+
+ return ghcb;
+}
+
+static void sev_es_put_ghcb(struct ghcb_state *state)
+{
+ struct sev_es_runtime_data *data;
+ struct ghcb *ghcb;
+
+ data = this_cpu_read(runtime_data);
+ ghcb = &data->ghcb_page;
+
+ if (state->ghcb) {
+ /* Restore GHCB from Backup */
+ *ghcb = *state->ghcb;
+ data->backup_ghcb_active = false;
+ state->ghcb = NULL;
+ } else {
+ data->ghcb_active = false;
+ }
+}
+
/* Needed in vc_early_vc_forward_exception */
void do_early_exception(struct pt_regs *regs, int trapnr);

@@ -263,6 +327,9 @@ static void __init sev_es_init_ghcb(int cpu)
panic("Can not map GHCBs unencrypted");

memset(&data->ghcb_page, 0, sizeof(data->ghcb_page));
+
+ data->ghcb_active = false;
+ data->backup_ghcb_active = false;
}

static void __init init_vc_stack_names(void)
@@ -367,6 +434,104 @@ static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
return result;
}

+static void vc_forward_exception(struct es_em_ctxt *ctxt)
+{
+ long error_code = ctxt->fi.error_code;
+ int trapnr = ctxt->fi.vector;
+
+ ctxt->regs->orig_ax = ctxt->fi.error_code;
+
+ switch (trapnr) {
+ case X86_TRAP_GP:
+ do_general_protection(ctxt->regs, error_code);
+ break;
+ case X86_TRAP_UD:
+ do_invalid_op(ctxt->regs, 0);
+ break;
+ default:
+ pr_emerg("ERROR: Unsupported exception in #VC instruction emulation - can't continue\n");
+ BUG();
+ }
+}
+
+dotraplinkage void do_vmm_communication(struct pt_regs *regs,
+ unsigned long exit_code)
+{
+ struct sev_es_runtime_data *data = this_cpu_read(runtime_data);
+ struct ghcb_state state;
+ struct es_em_ctxt ctxt;
+ enum es_result result;
+ struct ghcb *ghcb;
+
+ lockdep_assert_irqs_disabled();
+
+ /*
+ * This is invoked through an interrupt gate, so IRQs are disabled. The
+ * code below might walk page-tables for user or kernel addresses, so
+ * keep the IRQs disabled to protect us against concurrent TLB flushes.
+ */
+
+ ghcb = sev_es_get_ghcb(&state);
+ if (!ghcb) {
+ /*
+ * Mark GHCBs inactive so that panic() is able to print the
+ * message.
+ */
+ data->ghcb_active = false;
+ data->backup_ghcb_active = false;
+
+ panic("Unable to handle #VC exception! GHCB and Backup GHCB are already in use");
+ }
+
+ vc_ghcb_invalidate(ghcb);
+ result = vc_init_em_ctxt(&ctxt, regs, exit_code);
+
+ if (result == ES_OK)
+ result = vc_handle_exitcode(&ctxt, ghcb, exit_code);
+
+ sev_es_put_ghcb(&state);
+
+ /* Done - now check the result */
+ switch (result) {
+ case ES_OK:
+ vc_finish_insn(&ctxt);
+ break;
+ case ES_UNSUPPORTED:
+ pr_emerg("PANIC: Unsupported exit-code 0x%02lx in early #VC exception (IP: 0x%lx)\n",
+ exit_code, regs->ip);
+ goto fail;
+ case ES_VMM_ERROR:
+ pr_emerg("PANIC: Failure in communication with VMM (exit-code 0x%02lx IP: 0x%lx)\n",
+ exit_code, regs->ip);
+ goto fail;
+ case ES_DECODE_FAILED:
+ pr_emerg("PANIC: Failed to decode instruction (exit-code 0x%02lx IP: 0x%lx)\n",
+ exit_code, regs->ip);
+ goto fail;
+ case ES_EXCEPTION:
+ vc_forward_exception(&ctxt);
+ break;
+ case ES_RETRY:
+ /* Nothing to do */
+ break;
+ default:
+ pr_emerg("PANIC: Unknown result in %s():%d\n", __func__, result);
+ /*
+ * Emulating the instruction which caused the #VC exception
+ * failed - can't continue so print debug information
+ */
+ BUG();
+ }
+
+ return;
+
+fail:
+ show_regs(regs);
+
+ while (true)
+ halt();
+}
+
bool __init vc_boot_ghcb(struct pt_regs *regs)
{
unsigned long exit_code = regs->orig_ax;
--
2.17.1