x86/sev-es: Allocate and map an IST stack for #VC handler

Allocate and map an IST stack and an additional fall-back stack for
the #VC handler.  The memory for the stacks is allocated only when
SEV-ES is active.

The #VC handler needs to use an IST stack because a #VC exception can be
raised from kernel space with unsafe stack, e.g. in the SYSCALL entry
path.

Since the #VC exception can be nested, the #VC handler switches back to
the interrupted stack when entered from kernel space. If switching back
is not possible, the fall-back stack is used.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-43-joro@8bytes.org

1 files changed, 33 insertions, 0 deletions

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 720b1b671812..fae8145e4acf 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -17,6 +17,7 @@
 #include <linux/kernel.h>
 #include <linux/mm.h>
 
+#include <asm/cpu_entry_area.h>
 #include <asm/sev-es.h>
 #include <asm/insn-eval.h>
 #include <asm/fpu/internal.h>
@@ -37,10 +38,41 @@ static struct ghcb __initdata *boot_ghcb;
 /* #VC handler runtime per-CPU data */
 struct sev_es_runtime_data {
 	struct ghcb ghcb_page;
+
+	/* Physical storage for the per-CPU IST stack of the #VC handler */
+	char ist_stack[EXCEPTION_STKSZ] __aligned(PAGE_SIZE);
+
+	/*
+	 * Physical storage for the per-CPU fall-back stack of the #VC handler.
+	 * The fall-back stack is used when it is not safe to switch back to the
+	 * interrupted stack in the #VC entry code.
+	 */
+	char fallback_stack[EXCEPTION_STKSZ] __aligned(PAGE_SIZE);
 };
 
 static DEFINE_PER_CPU(struct sev_es_runtime_data*, runtime_data);
 
+static void __init setup_vc_stacks(int cpu)
+{
+	struct sev_es_runtime_data *data;
+	struct cpu_entry_area *cea;
+	unsigned long vaddr;
+	phys_addr_t pa;
+
+	data = per_cpu(runtime_data, cpu);
+	cea  = get_cpu_entry_area(cpu);
+
+	/* Map #VC IST stack */
+	vaddr = CEA_ESTACK_BOT(&cea->estacks, VC);
+	pa    = __pa(data->ist_stack);
+	cea_set_pte((void *)vaddr, pa, PAGE_KERNEL);
+
+	/* Map VC fall-back stack */
+	vaddr = CEA_ESTACK_BOT(&cea->estacks, VC2);
+	pa    = __pa(data->fallback_stack);
+	cea_set_pte((void *)vaddr, pa, PAGE_KERNEL);
+}
+
 /* Needed in vc_early_forward_exception */
 void do_early_exception(struct pt_regs *regs, int trapnr);
 
@@ -249,6 +281,7 @@ void __init sev_es_init_vc_handling(void)
 	for_each_possible_cpu(cpu) {
 		alloc_runtime_data(cpu);
 		init_ghcb(cpu);
+		setup_vc_stacks(cpu);
 	}
 }