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x86/entry/64: Make cpu_entry_area.tss read-only 

The TSS is a fairly juicy target for exploits, and, now that the TSS
is in the cpu_entry_area, it's no longer protected by kASLR.  Make it
read-only on x86_64.

On x86_32, it can't be RO because it's written by the CPU during task
switches, and we use a task gate for double faults.  I'd also be
nervous about errata if we tried to make it RO even on configurations
without double fault handling.

[ tglx: AMD confirmed that there is no problem on 64-bit with TSS RO.  So
  	it's probably safe to assume that it's a non issue, though Intel
  	might have been creative in that area. Still waiting for
  	confirmation. ]

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bpetkov@suse.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Link: https://lkml.kernel.org/r/20171204150606.733700132@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2017-12-04 15:07:29 +01:00 committed by Ingo Molnar
parent 0f9a48100f
commit c482feefe1
16 changed files with 60 additions and 48 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
arch/x86/entry/entry_32.S
View File

@ -942,7 +942,7 @@ ENTRY(debug)
/* Are we currently on the SYSENTER stack? */
movl PER_CPU_VAR(cpu_entry_area), %ecx
addl $CPU_ENTRY_AREA_tss + TSS_STRUCT_SYSENTER_stack + SIZEOF_SYSENTER_stack, %ecx
addl $CPU_ENTRY_AREA_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
@ -986,7 +986,7 @@ ENTRY(nmi)
/* Are we currently on the SYSENTER stack? */
movl PER_CPU_VAR(cpu_entry_area), %ecx
addl $CPU_ENTRY_AREA_tss + TSS_STRUCT_SYSENTER_stack + SIZEOF_SYSENTER_stack, %ecx
addl $CPU_ENTRY_AREA_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

8
arch/x86/entry/entry_64.S
View File

@ -154,7 +154,7 @@ END(native_usergs_sysret64)
_entry_trampoline - CPU_ENTRY_AREA_entry_trampoline(%rip)
/* The top word of the SYSENTER stack is hot and is usable as scratch space. */
#define RSP_SCRATCH CPU_ENTRY_AREA_tss + TSS_STRUCT_SYSENTER_stack + \
#define RSP_SCRATCH CPU_ENTRY_AREA_SYSENTER_stack + \
SIZEOF_SYSENTER_stack - 8 + CPU_ENTRY_AREA
ENTRY(entry_SYSCALL_64_trampoline)
@ -390,7 +390,7 @@ syscall_return_via_sysret:
* Save old stack pointer and switch to trampoline stack.
*/
movq %rsp, %rdi
movq PER_CPU_VAR(cpu_tss + TSS_sp0), %rsp
movq PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp
pushq RSP-RDI(%rdi) /* RSP */
pushq (%rdi) /* RDI */
@ -719,7 +719,7 @@ GLOBAL(swapgs_restore_regs_and_return_to_usermode)
* Save old stack pointer and switch to trampoline stack.
*/
movq %rsp, %rdi
movq PER_CPU_VAR(cpu_tss + TSS_sp0), %rsp
movq PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %rsp
/* Copy the IRET frame to the trampoline stack. */
pushq 6*8(%rdi) /* SS */
@ -934,7 +934,7 @@ apicinterrupt IRQ_WORK_VECTOR irq_work_interrupt smp_irq_work_interrupt
/*
* Exception entry points.
*/
#define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss) + (TSS_ist + ((x) - 1) * 8)
#define CPU_TSS_IST(x) PER_CPU_VAR(cpu_tss_rw) + (TSS_ist + ((x) - 1) * 8)
/*
* Switch to the thread stack. This is called with the IRET frame and

13
arch/x86/include/asm/fixmap.h
View File

@ -56,9 +56,14 @@ 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.
* The GDT is just below SYSENTER_stack and thus serves (on x86_64) as
* a a read-only guard page.
*/
struct SYSENTER_stack_page SYSENTER_stack_page;
/*
* On x86_64, the TSS is mapped RO. On x86_32, it's mapped RW because
* we need task switches to work, and task switches write to the TSS.
*/
struct tss_struct tss;
@ -247,7 +252,7 @@ static inline struct cpu_entry_area *get_cpu_entry_area(int cpu)
static inline struct SYSENTER_stack *cpu_SYSENTER_stack(int cpu)
{
return &get_cpu_entry_area(cpu)->tss.SYSENTER_stack;
return &get_cpu_entry_area(cpu)->SYSENTER_stack_page.stack;
}
#endif /* !__ASSEMBLY__ */

17
arch/x86/include/asm/processor.h
View File

@ -340,13 +340,11 @@ struct SYSENTER_stack {
unsigned long words[64];
};
struct tss_struct {
/*
* Space for the temporary SYSENTER stack, used for SYSENTER
* and the entry trampoline as well.
*/
struct SYSENTER_stack SYSENTER_stack;
struct SYSENTER_stack_page {
struct SYSENTER_stack stack;
} __aligned(PAGE_SIZE);
struct tss_struct {
/*
* The fixed hardware portion. This must not cross a page boundary
* at risk of violating the SDM's advice and potentially triggering
@ -363,7 +361,7 @@ struct tss_struct {
unsigned long io_bitmap[IO_BITMAP_LONGS + 1];
} __aligned(PAGE_SIZE);
DECLARE_PER_CPU_PAGE_ALIGNED(struct tss_struct, cpu_tss);
DECLARE_PER_CPU_PAGE_ALIGNED(struct tss_struct, cpu_tss_rw);
/*
* sizeof(unsigned long) coming from an extra "long" at the end
@ -378,7 +376,8 @@ DECLARE_PER_CPU_PAGE_ALIGNED(struct tss_struct, cpu_tss);
#ifdef CONFIG_X86_32
DECLARE_PER_CPU(unsigned long, cpu_current_top_of_stack);
#else
#define cpu_current_top_of_stack cpu_tss.x86_tss.sp1
/* The RO copy can't be accessed with this_cpu_xyz(), so use the RW copy. */
#define cpu_current_top_of_stack cpu_tss_rw.x86_tss.sp1
#endif
/*
@ -538,7 +537,7 @@ static inline void native_set_iopl_mask(unsigned mask)
static inline void
native_load_sp0(unsigned long sp0)
{
this_cpu_write(cpu_tss.x86_tss.sp0, sp0);
this_cpu_write(cpu_tss_rw.x86_tss.sp0, sp0);
}
static inline void native_swapgs(void)

4
arch/x86/include/asm/switch_to.h
View File

@ -79,10 +79,10 @@ do { \
static inline void refresh_sysenter_cs(struct thread_struct *thread)
{
/* Only happens when SEP is enabled, no need to test "SEP"arately: */
if (unlikely(this_cpu_read(cpu_tss.x86_tss.ss1) == thread->sysenter_cs))
if (unlikely(this_cpu_read(cpu_tss_rw.x86_tss.ss1) == thread->sysenter_cs))
return;
this_cpu_write(cpu_tss.x86_tss.ss1, thread->sysenter_cs);
this_cpu_write(cpu_tss_rw.x86_tss.ss1, thread->sysenter_cs);
wrmsr(MSR_IA32_SYSENTER_CS, thread->sysenter_cs, 0);
}
#endif

2
arch/x86/include/asm/thread_info.h
View File

@ -207,7 +207,7 @@ static inline int arch_within_stack_frames(const void * const stack,
#else /* !__ASSEMBLY__ */
#ifdef CONFIG_X86_64
# define cpu_current_top_of_stack (cpu_tss + TSS_sp1)
# define cpu_current_top_of_stack (cpu_tss_rw + TSS_sp1)
#endif
#endif

5
arch/x86/kernel/asm-offsets.c
View File

@ -94,10 +94,9 @@ void common(void) {
BLANK();
DEFINE(PTREGS_SIZE, sizeof(struct pt_regs));
OFFSET(TSS_STRUCT_SYSENTER_stack, tss_struct, SYSENTER_stack);
DEFINE(SIZEOF_SYSENTER_stack, sizeof(struct SYSENTER_stack));
/* Layout info for cpu_entry_area */
OFFSET(CPU_ENTRY_AREA_tss, cpu_entry_area, tss);
OFFSET(CPU_ENTRY_AREA_entry_trampoline, cpu_entry_area, entry_trampoline);
OFFSET(CPU_ENTRY_AREA_SYSENTER_stack, cpu_entry_area, SYSENTER_stack_page);
DEFINE(SIZEOF_SYSENTER_stack, sizeof(struct SYSENTER_stack));
}

4
arch/x86/kernel/asm-offsets_32.c
View File

@ -47,8 +47,8 @@ void foo(void)
BLANK();
/* Offset from the sysenter stack to tss.sp0 */
DEFINE(TSS_sysenter_sp0, offsetof(struct tss_struct, x86_tss.sp0) -
offsetofend(struct tss_struct, SYSENTER_stack));
DEFINE(TSS_sysenter_sp0, offsetof(struct cpu_entry_area, tss.x86_tss.sp0) -
offsetofend(struct cpu_entry_area, SYSENTER_stack_page.stack));
#ifdef CONFIG_CC_STACKPROTECTOR
BLANK();

29
arch/x86/kernel/cpu/common.c
View File

@ -487,6 +487,9 @@ static DEFINE_PER_CPU_PAGE_ALIGNED(char, exception_stacks
[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ]);
#endif
static DEFINE_PER_CPU_PAGE_ALIGNED(struct SYSENTER_stack_page,
SYSENTER_stack_storage);
static void __init
set_percpu_fixmap_pages(int idx, void *ptr, int pages, pgprot_t prot)
{
@ -500,23 +503,29 @@ static void __init setup_cpu_entry_area(int cpu)
#ifdef CONFIG_X86_64
extern char _entry_trampoline[];
/* On 64-bit systems, we use a read-only fixmap GDT. */
/* On 64-bit systems, we use a read-only fixmap GDT and TSS. */
pgprot_t gdt_prot = PAGE_KERNEL_RO;
pgprot_t tss_prot = PAGE_KERNEL_RO;
#else
/*
* On native 32-bit systems, the GDT cannot be read-only because
* our double fault handler uses a task gate, and entering through
* a task gate needs to change an available TSS to busy. If the GDT
* is read-only, that will triple fault.
* a task gate needs to change an available TSS to busy. If the
* GDT is read-only, that will triple fault. The TSS cannot be
* read-only because the CPU writes to it on task switches.
*
* On Xen PV, the GDT must be read-only because the hypervisor requires
* it.
* On Xen PV, the GDT must be read-only because the hypervisor
* requires it.
*/
pgprot_t gdt_prot = boot_cpu_has(X86_FEATURE_XENPV) ?
PAGE_KERNEL_RO : PAGE_KERNEL;
pgprot_t tss_prot = PAGE_KERNEL;
#endif
__set_fixmap(get_cpu_entry_area_index(cpu, gdt), get_cpu_gdt_paddr(cpu), gdt_prot);
set_percpu_fixmap_pages(get_cpu_entry_area_index(cpu, SYSENTER_stack_page),
per_cpu_ptr(&SYSENTER_stack_storage, cpu), 1,
PAGE_KERNEL);
/*
* The Intel SDM says (Volume 3, 7.2.1):
@ -539,9 +548,9 @@ static void __init setup_cpu_entry_area(int cpu)
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),
&per_cpu(cpu_tss_rw, cpu),
sizeof(struct tss_struct) / PAGE_SIZE,
PAGE_KERNEL);
tss_prot);
#ifdef CONFIG_X86_32
per_cpu(cpu_entry_area, cpu) = get_cpu_entry_area(cpu);
@ -1305,7 +1314,7 @@ void enable_sep_cpu(void)
return;
cpu = get_cpu();
tss = &per_cpu(cpu_tss, cpu);
tss = &per_cpu(cpu_tss_rw, cpu);
/*
* We cache MSR_IA32_SYSENTER_CS's value in the TSS's ss1 field --
@ -1575,7 +1584,7 @@ void cpu_init(void)
if (cpu)
load_ucode_ap();
t = &per_cpu(cpu_tss, cpu);
t = &per_cpu(cpu_tss_rw, cpu);
oist = &per_cpu(orig_ist, cpu);
#ifdef CONFIG_NUMA
@ -1667,7 +1676,7 @@ void cpu_init(void)
{
int cpu = smp_processor_id();
struct task_struct *curr = current;
struct tss_struct *t = &per_cpu(cpu_tss, cpu);
struct tss_struct *t = &per_cpu(cpu_tss_rw, cpu);
wait_for_master_cpu(cpu);

2
arch/x86/kernel/ioport.c
View File

@ -67,7 +67,7 @@ asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on)
* because the ->io_bitmap_max value must match the bitmap
* contents:
*/
tss = &per_cpu(cpu_tss, get_cpu());
tss = &per_cpu(cpu_tss_rw, get_cpu());
if (turn_on)
bitmap_clear(t->io_bitmap_ptr, from, num);

6
arch/x86/kernel/process.c
View File

@ -47,7 +47,7 @@
* section. Since TSS's are completely CPU-local, we want them
* on exact cacheline boundaries, to eliminate cacheline ping-pong.
*/
__visible DEFINE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss) = {
__visible DEFINE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss_rw) = {
.x86_tss = {
/*
* .sp0 is only used when entering ring 0 from a lower
@ -82,7 +82,7 @@ __visible DEFINE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss) = {
.io_bitmap = { [0 ... IO_BITMAP_LONGS] = ~0 },
#endif
};
EXPORT_PER_CPU_SYMBOL(cpu_tss);
EXPORT_PER_CPU_SYMBOL(cpu_tss_rw);
DEFINE_PER_CPU(bool, __tss_limit_invalid);
EXPORT_PER_CPU_SYMBOL_GPL(__tss_limit_invalid);
@ -111,7 +111,7 @@ void exit_thread(struct task_struct *tsk)
struct fpu *fpu = &t->fpu;
if (bp) {
struct tss_struct *tss = &per_cpu(cpu_tss, get_cpu());
struct tss_struct *tss = &per_cpu(cpu_tss_rw, get_cpu());
t->io_bitmap_ptr = NULL;
clear_thread_flag(TIF_IO_BITMAP);

2
arch/x86/kernel/process_32.c
View File

@ -234,7 +234,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
struct fpu *prev_fpu = &prev->fpu;
struct fpu *next_fpu = &next->fpu;
int cpu = smp_processor_id();
struct tss_struct *tss = &per_cpu(cpu_tss, cpu);
struct tss_struct *tss = &per_cpu(cpu_tss_rw, cpu);
/* never put a printk in __switch_to... printk() calls wake_up*() indirectly */

2
arch/x86/kernel/process_64.c
View File

@ -399,7 +399,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
struct fpu *prev_fpu = &prev->fpu;
struct fpu *next_fpu = &next->fpu;
int cpu = smp_processor_id();
struct tss_struct *tss = &per_cpu(cpu_tss, cpu);
struct tss_struct *tss = &per_cpu(cpu_tss_rw, cpu);
WARN_ON_ONCE(IS_ENABLED(CONFIG_DEBUG_ENTRY) &&
this_cpu_read(irq_count) != -1);

4
arch/x86/kernel/traps.c
View File

@ -364,7 +364,7 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
regs->cs == __KERNEL_CS &&
regs->ip == (unsigned long)native_irq_return_iret)
{
struct pt_regs *gpregs = (struct pt_regs *)this_cpu_read(cpu_tss.x86_tss.sp0) - 1;
struct pt_regs *gpregs = (struct pt_regs *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
/*
* regs->sp points to the failing IRET frame on the
@ -649,7 +649,7 @@ struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
* exception came from the IRET target.
*/
struct bad_iret_stack *new_stack =
(struct bad_iret_stack *)this_cpu_read(cpu_tss.x86_tss.sp0) - 1;
(struct bad_iret_stack *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
/* Copy the IRET target to the new stack. */
memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);

4
arch/x86/lib/delay.c
View File

@ -107,10 +107,10 @@ static void delay_mwaitx(unsigned long __loops)
delay = min_t(u64, MWAITX_MAX_LOOPS, loops);
/*
* Use cpu_tss as a cacheline-aligned, seldomly
* Use cpu_tss_rw as a cacheline-aligned, seldomly
* accessed per-cpu variable as the monitor target.
*/
__monitorx(raw_cpu_ptr(&cpu_tss), 0, 0);
__monitorx(raw_cpu_ptr(&cpu_tss_rw), 0, 0);
/*
* AMD, like Intel, supports the EAX hint and EAX=0xf

2
arch/x86/xen/enlighten_pv.c
View File

@ -818,7 +818,7 @@ static void xen_load_sp0(unsigned long sp0)
mcs = xen_mc_entry(0);
MULTI_stack_switch(mcs.mc, __KERNEL_DS, sp0);
xen_mc_issue(PARAVIRT_LAZY_CPU);
this_cpu_write(cpu_tss.x86_tss.sp0, sp0);
this_cpu_write(cpu_tss_rw.x86_tss.sp0, sp0);
}
void xen_set_iopl_mask(unsigned mask)