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Subject[patch 14/60] x86/entry: Remap the TSS into the CPU entry area
From: Andy Lutomirski <luto@kernel.org>

This has a secondary purpose: it puts the entry stack into a region
with a well-controlled layout. A subsequent patch will take
advantage of this to streamline the SYSCALL entry code to be able to
find it more easily.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lkml.kernel.org/r/cdcba7e1e82122461b3ca36bb3ef6713ba605e35.1511497875.git.luto@kernel.org

---
arch/x86/entry/entry_32.S | 6 ++++--
arch/x86/include/asm/fixmap.h | 7 +++++++
arch/x86/kernel/asm-offsets.c | 3 +++
arch/x86/kernel/cpu/common.c | 41 +++++++++++++++++++++++++++++++++++------
arch/x86/kernel/dumpstack.c | 3 ++-
arch/x86/kvm/vmx.c | 2 +-
arch/x86/power/cpu.c | 11 ++++++-----
7 files changed, 58 insertions(+), 15 deletions(-)

--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -941,7 +941,8 @@ ENTRY(debug)
movl %esp, %eax # pt_regs pointer

/* Are we currently on the SYSENTER stack? */
- PER_CPU(cpu_tss + CPU_TSS_SYSENTER_stack + SIZEOF_SYSENTER_stack, %ecx)
+ movl PER_CPU_VAR(cpu_entry_area), %ecx
+ addl $CPU_ENTRY_AREA_tss + CPU_TSS_SYSENTER_stack + SIZEOF_SYSENTER_stack, %ecx
subl %eax, %ecx /* ecx = (end of SYSENTER_stack) - esp */
cmpl $SIZEOF_SYSENTER_stack, %ecx
jb .Ldebug_from_sysenter_stack
@@ -984,7 +985,8 @@ ENTRY(nmi)
movl %esp, %eax # pt_regs pointer

/* Are we currently on the SYSENTER stack? */
- PER_CPU(cpu_tss + CPU_TSS_SYSENTER_stack + SIZEOF_SYSENTER_stack, %ecx)
+ movl PER_CPU_VAR(cpu_entry_area), %ecx
+ addl $CPU_ENTRY_AREA_tss + CPU_TSS_SYSENTER_stack + SIZEOF_SYSENTER_stack, %ecx
subl %eax, %ecx /* ecx = (end of SYSENTER_stack) - esp */
cmpl $SIZEOF_SYSENTER_stack, %ecx
jb .Lnmi_from_sysenter_stack
--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -54,6 +54,13 @@ extern unsigned long __FIXADDR_TOP;
*/
struct cpu_entry_area {
char gdt[PAGE_SIZE];
+
+ /*
+ * The GDT is just below cpu_tss and thus serves (on x86_64) as a
+ * a read-only guard page for the SYSENTER stack at the bottom
+ * of the TSS region.
+ */
+ struct tss_struct tss;
};

#define CPU_ENTRY_AREA_PAGES (sizeof(struct cpu_entry_area) / PAGE_SIZE)
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -98,4 +98,7 @@ void common(void) {
OFFSET(CPU_TSS_SYSENTER_stack, tss_struct, SYSENTER_stack);
/* Size of SYSENTER_stack */
DEFINE(SIZEOF_SYSENTER_stack, sizeof(((struct tss_struct *)0)->SYSENTER_stack));
+
+ /* Layout info for cpu_entry_area */
+ OFFSET(CPU_ENTRY_AREA_tss, cpu_entry_area, tss);
}
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -490,6 +490,22 @@ void load_percpu_segment(int cpu)
load_stack_canary_segment();
}

+static void set_percpu_fixmap_pages(int fixmap_index, void *ptr,
+ int pages, pgprot_t prot)
+{
+ int i;
+
+ for (i = 0; i < pages; i++) {
+ __set_fixmap(fixmap_index - i,
+ per_cpu_ptr_to_phys(ptr + i * PAGE_SIZE), prot);
+ }
+}
+
+#ifdef CONFIG_X86_32
+/* The 32-bit entry code needs to find cpu_entry_area. */
+DEFINE_PER_CPU(struct cpu_entry_area *, cpu_entry_area);
+#endif
+
/* Setup the fixmap mappings only once per-processor */
static inline void setup_cpu_entry_area(int cpu)
{
@@ -531,7 +547,15 @@ static inline void setup_cpu_entry_area(
*/
BUILD_BUG_ON((offsetof(struct tss_struct, x86_tss) ^
offsetofend(struct tss_struct, x86_tss)) & PAGE_MASK);
+ BUILD_BUG_ON(sizeof(struct tss_struct) % PAGE_SIZE != 0);
+ set_percpu_fixmap_pages(get_cpu_entry_area_index(cpu, tss),
+ &per_cpu(cpu_tss, cpu),
+ sizeof(struct tss_struct) / PAGE_SIZE,
+ PAGE_KERNEL);

+#ifdef CONFIG_X86_32
+ this_cpu_write(cpu_entry_area, get_cpu_entry_area(cpu));
+#endif
}

/* Load the original GDT from the per-cpu structure */
@@ -1282,7 +1306,8 @@ void enable_sep_cpu(void)
wrmsr(MSR_IA32_SYSENTER_CS, tss->x86_tss.ss1, 0);

wrmsr(MSR_IA32_SYSENTER_ESP,
- (unsigned long)tss + offsetofend(struct tss_struct, SYSENTER_stack),
+ (unsigned long)&get_cpu_entry_area(cpu)->tss +
+ offsetofend(struct tss_struct, SYSENTER_stack),
0);

wrmsr(MSR_IA32_SYSENTER_EIP, (unsigned long)entry_SYSENTER_32, 0);
@@ -1395,6 +1420,8 @@ static DEFINE_PER_CPU_PAGE_ALIGNED(char,
/* May not be marked __init: used by software suspend */
void syscall_init(void)
{
+ int cpu = smp_processor_id();
+
wrmsr(MSR_STAR, 0, (__USER32_CS << 16) | __KERNEL_CS);
wrmsrl(MSR_LSTAR, (unsigned long)entry_SYSCALL_64);

@@ -1408,7 +1435,7 @@ void syscall_init(void)
*/
wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)__KERNEL_CS);
wrmsrl_safe(MSR_IA32_SYSENTER_ESP,
- (unsigned long)this_cpu_ptr(&cpu_tss) +
+ (unsigned long)&get_cpu_entry_area(cpu)->tss +
offsetofend(struct tss_struct, SYSENTER_stack));
wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat);
#else
@@ -1618,11 +1645,13 @@ void cpu_init(void)
initialize_tlbstate_and_flush();
enter_lazy_tlb(&init_mm, me);

+ setup_cpu_entry_area(cpu);
+
/*
* Initialize the TSS. Don't bother initializing sp0, as the initial
* task never enters user mode.
*/
- set_tss_desc(cpu, &t->x86_tss);
+ set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
load_TR_desc();

load_mm_ldt(&init_mm);
@@ -1635,7 +1664,6 @@ void cpu_init(void)
if (is_uv_system())
uv_cpu_init();

- setup_cpu_entry_area(cpu);
load_fixmap_gdt(cpu);
}

@@ -1676,11 +1704,13 @@ void cpu_init(void)
initialize_tlbstate_and_flush();
enter_lazy_tlb(&init_mm, curr);

+ setup_cpu_entry_area(cpu);
+
/*
* Initialize the TSS. Don't bother initializing sp0, as the initial
* task never enters user mode.
*/
- set_tss_desc(cpu, &t->x86_tss);
+ set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);
load_TR_desc();

load_mm_ldt(&init_mm);
@@ -1697,7 +1727,6 @@ void cpu_init(void)

fpu__init_cpu();

- setup_cpu_entry_area(cpu);
load_fixmap_gdt(cpu);
}
#endif
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -45,7 +45,8 @@ bool in_task_stack(unsigned long *stack,

bool in_sysenter_stack(unsigned long *stack, struct stack_info *info)
{
- struct tss_struct *tss = this_cpu_ptr(&cpu_tss);
+ int cpu = smp_processor_id();
+ struct tss_struct *tss = &get_cpu_entry_area(cpu)->tss;

/* Treat the canary as part of the stack for unwinding purposes. */
void *begin = &tss->SYSENTER_stack_canary;
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2291,7 +2291,7 @@ static void vmx_vcpu_load(struct kvm_vcp
* processors. See 22.2.4.
*/
vmcs_writel(HOST_TR_BASE,
- (unsigned long)this_cpu_ptr(&cpu_tss.x86_tss));
+ (unsigned long)&get_cpu_entry_area(cpu)->tss.x86_tss);
vmcs_writel(HOST_GDTR_BASE, (unsigned long)gdt); /* 22.2.4 */

/*
--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -160,18 +160,19 @@ static void do_fpu_end(void)
static void fix_processor_context(void)
{
int cpu = smp_processor_id();
- struct tss_struct *t = &per_cpu(cpu_tss, cpu);
#ifdef CONFIG_X86_64
struct desc_struct *desc = get_cpu_gdt_rw(cpu);
tss_desc tss;
#endif

/*
- * This just modifies memory; should not be necessary. But... This is
- * necessary, because 386 hardware has concept of busy TSS or some
- * similar stupidity.
+ * We need to reload TR, which requires that we change the
+ * GDT entry to indicate "available" first.
+ *
+ * XXX: This could probably all be replaced by a call to
+ * force_reload_TR().
*/
- set_tss_desc(cpu, &t->x86_tss);
+ set_tss_desc(cpu, &get_cpu_entry_area(cpu)->tss.x86_tss);

#ifdef CONFIG_X86_64
memcpy(&tss, &desc[GDT_ENTRY_TSS], sizeof(tss_desc));

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