[PATCH v5 44/75] x86/sev-es: Allocate and Map IST stack for #VC handler

Joerg Roedel
2020-07-24T16:04:42Z

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 it could 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>
---
arch/x86/include/asm/cpu_entry_area.h | 33 +++++++++++++++++----------
arch/x86/include/asm/page_64_types.h | 1 +
arch/x86/kernel/cpu/common.c | 2 ++
arch/x86/kernel/dumpstack_64.c | 8 +++++--
arch/x86/kernel/sev-es.c | 33 +++++++++++++++++++++++++++
5 files changed, 63 insertions(+), 14 deletions(-)

diff --git a/arch/x86/include/asm/cpu_entry_area.h b/arch/x86/include/asm/cpu_entry_area.h
index 8902fdb7de13..f87e4c0c16f4 100644
--- a/arch/x86/include/asm/cpu_entry_area.h
+++ b/arch/x86/include/asm/cpu_entry_area.h
@@ -11,25 +11,29 @@
#ifdef CONFIG_X86_64

/* Macro to enforce the same ordering and stack sizes */
-#define ESTACKS_MEMBERS(guardsize) \
- char DF_stack_guard[guardsize]; \
- char DF_stack[EXCEPTION_STKSZ]; \
- char NMI_stack_guard[guardsize]; \
- char NMI_stack[EXCEPTION_STKSZ]; \
- char DB_stack_guard[guardsize]; \
- char DB_stack[EXCEPTION_STKSZ]; \
- char MCE_stack_guard[guardsize]; \
- char MCE_stack[EXCEPTION_STKSZ]; \
- char IST_top_guard[guardsize]; \
+#define ESTACKS_MEMBERS(guardsize, optional_stack_size) \
+ char DF_stack_guard[guardsize]; \
+ char DF_stack[EXCEPTION_STKSZ]; \
+ char NMI_stack_guard[guardsize]; \
+ char NMI_stack[EXCEPTION_STKSZ]; \
+ char DB_stack_guard[guardsize]; \
+ char DB_stack[EXCEPTION_STKSZ]; \
+ char MCE_stack_guard[guardsize]; \
+ char MCE_stack[EXCEPTION_STKSZ]; \
+ char VC_stack_guard[guardsize]; \
+ char VC_stack[optional_stack_size]; \
+ char VC2_stack_guard[guardsize]; \
+ char VC2_stack[optional_stack_size]; \
+ char IST_top_guard[guardsize]; \

/* The exception stacks' physical storage. No guard pages required */
struct exception_stacks {
- ESTACKS_MEMBERS(0)
+ ESTACKS_MEMBERS(0, 0)
};

/* The effective cpu entry area mapping with guard pages. */
struct cea_exception_stacks {
- ESTACKS_MEMBERS(PAGE_SIZE)
+ ESTACKS_MEMBERS(PAGE_SIZE, EXCEPTION_STKSZ)
};

/*
@@ -40,6 +44,8 @@ enum exception_stack_ordering {
ESTACK_NMI,
ESTACK_DB,
ESTACK_MCE,
+ ESTACK_VC,
+ ESTACK_VC2,
N_EXCEPTION_STACKS
};

@@ -139,4 +145,7 @@ static inline struct entry_stack *cpu_entry_stack(int cpu)
#define __this_cpu_ist_top_va(name) \
CEA_ESTACK_TOP(__this_cpu_read(cea_exception_stacks), name)

+#define __this_cpu_ist_bot_va(name) \
+ CEA_ESTACK_BOT(__this_cpu_read(cea_exception_stacks), name)
+
#endif
diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
index 288b065955b7..d0c6c10c18a0 100644
--- a/arch/x86/include/asm/page_64_types.h
+++ b/arch/x86/include/asm/page_64_types.h
@@ -28,6 +28,7 @@
#define IST_INDEX_NMI 1
#define IST_INDEX_DB 2
#define IST_INDEX_MCE 3
+#define IST_INDEX_VC 4

/*
* Set __PAGE_OFFSET to the most negative possible address +
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 965474d78cef..86efa9c207e5 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1828,6 +1828,8 @@ static inline void tss_setup_ist(struct tss_struct *tss)
tss->x86_tss.ist[IST_INDEX_NMI] = __this_cpu_ist_top_va(NMI);
tss->x86_tss.ist[IST_INDEX_DB] = __this_cpu_ist_top_va(DB);
tss->x86_tss.ist[IST_INDEX_MCE] = __this_cpu_ist_top_va(MCE);
+ /* Only mapped when SEV-ES is active */
+ tss->x86_tss.ist[IST_INDEX_VC] = __this_cpu_ist_top_va(VC);
}

#else /* CONFIG_X86_64 */
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 4a94d38cd141..c49cf594714b 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -24,11 +24,13 @@ static const char * const exception_stack_names[] = {
[ ESTACK_NMI ] = "NMI",
[ ESTACK_DB ] = "#DB",
[ ESTACK_MCE ] = "#MC",
+ [ ESTACK_VC ] = "#VC",
+ [ ESTACK_VC2 ] = "#VC2",
};

const char *stack_type_name(enum stack_type type)
{
- BUILD_BUG_ON(N_EXCEPTION_STACKS != 4);
+ BUILD_BUG_ON(N_EXCEPTION_STACKS != 6);

if (type == STACK_TYPE_IRQ)
return "IRQ";
@@ -79,6 +81,8 @@ struct estack_pages estack_pages[CEA_ESTACK_PAGES] ____cacheline_aligned = {
EPAGERANGE(NMI),
EPAGERANGE(DB),
EPAGERANGE(MCE),
+ EPAGERANGE(VC),
+ EPAGERANGE(VC2),
};

static bool in_exception_stack(unsigned long *stack, struct stack_info *info)
@@ -88,7 +92,7 @@ static bool in_exception_stack(unsigned long *stack, struct stack_info *info)
struct pt_regs *regs;
unsigned int k;

- BUILD_BUG_ON(N_EXCEPTION_STACKS != 4);
+ BUILD_BUG_ON(N_EXCEPTION_STACKS != 6);

begin = (unsigned long)__this_cpu_read(cea_exception_stacks);
/*
diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 734afaee378d..64002d86a237 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 sev_es_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) {
sev_es_alloc_runtime_data(cpu);
sev_es_init_ghcb(cpu);
+ sev_es_setup_vc_stacks(cpu);
}
}

--
2.27.0