Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)
diff mbox

Message ID CA+55aFx=wdH4v7cD2F5Kq+jwDfV5cz9qTANgOwpMTC3MY=99AQ@mail.gmail.com
State New
Headers show

Commit Message

Linus Torvalds June 24, 2016, 6:11 p.m. UTC
On Fri, Jun 24, 2016 at 10:51 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> And in particular, the init_task stack initialization initialized it
> to the init_thread pointer. Which was definitely deadly.
>
> Let's see if that was it..

No, it's still broken. But it's *less* broken, so here's a new version
of the patch that at least gets some of the stack setup right, in my
hope that somebody will bother to look at this, and being less broken
might mean that somebody sees what else I missed..

                   Linus
This is a non-working attempt at moving the thread_info into the
    task_struct on x86

 arch/mn10300/include/asm/thread_info.h |  2 +-
 arch/mn10300/kernel/kgdb.c             |  3 ++-
 arch/tile/include/asm/thread_info.h    |  2 +-
 arch/tile/kernel/process.c             |  3 ++-
 arch/x86/Kconfig                       |  1 +
 arch/x86/entry/common.c                | 21 ++++++----------
 arch/x86/entry/entry_64.S              |  9 ++++---
 arch/x86/include/asm/kprobes.h         | 12 +++++-----
 arch/x86/include/asm/switch_to.h       |  6 ++---
 arch/x86/include/asm/thread_info.h     | 37 +++-------------------------
 arch/x86/kernel/dumpstack.c            |  2 +-
 arch/x86/kernel/irq_32.c               |  2 --
 arch/x86/kernel/irq_64.c               |  3 +--
 arch/x86/kernel/process.c              |  6 ++---
 arch/x86/um/ptrace_32.c                |  8 +++----
 include/linux/init_task.h              | 11 ++++++++-
 include/linux/sched.h                  | 16 +++++++++++--
 init/Kconfig                           |  3 +++
 init/init_task.c                       |  7 ++++--
 kernel/fork.c                          | 44 +++++++++++++++++-----------------
 20 files changed, 93 insertions(+), 105 deletions(-)

Comments

Josh Poimboeuf June 24, 2016, 8:25 p.m. UTC | #1
On Fri, Jun 24, 2016 at 11:11:47AM -0700, Linus Torvalds wrote:
> On Fri, Jun 24, 2016 at 10:51 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > And in particular, the init_task stack initialization initialized it
> > to the init_thread pointer. Which was definitely deadly.
> >
> > Let's see if that was it..
> 
> No, it's still broken. But it's *less* broken, so here's a new version
> of the patch that at least gets some of the stack setup right, in my
> hope that somebody will bother to look at this, and being less broken
> might mean that somebody sees what else I missed..

I found at least one bug.  The changing of task->stack from a "void *" to an
"unsigned long *":

> -	void *stack;
> +	unsigned long *stack;

That subtly changes the pointer arithmetic in do_boot_cpu():


	idle->thread.sp = (unsigned long) (((struct pt_regs *)
			  (THREAD_SIZE +  task_stack_page(idle))) - 1);


That ends up adding 128k to the stack page bottom instead of 16k.

But fixing that doesn't seem to fix this:

[18446743832.576241] ------------[ cut here ]------------
[18446743832.576241] WARNING: CPU: 1 PID: 0 at /home/jpoimboe/git/linux/arch/x86/kernel/cpu/common.c:1434 cpu_init+0x34b/0x440
[18446743832.576241] Modules linked in:
[18446743832.576241] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.7.0-rc4+ #47
[18446743832.576241] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.1-20150318_183358- 04/01/2014
[18446743832.576241]  0000000000000086 574e5e6c6855ace9 ffff88007c553e88 ffffffff8143cb83
[18446743832.576241]  0000000000000000 0000000000000000 ffff88007c553ec8 ffffffff810b0e7b
[18446743832.576241]  0000059a00000000 0000000000000000 0000000000000000 0000000000000000
[18446743832.576241] Call Trace:
[18446743832.576241]  [<ffffffff8143cb83>] dump_stack+0x85/0xc2
[18446743832.576241]  [<ffffffff810b0e7b>] __warn+0xcb/0xf0
[18446743832.576241]  [<ffffffff810b0fad>] warn_slowpath_null+0x1d/0x20
[18446743832.576241]  [<ffffffff810491bb>] cpu_init+0x34b/0x440
[18446743832.576241]  [<ffffffff8105ab7c>] start_secondary+0x1c/0x1a0
[18446743832.576241] ---[ end trace 924d57afbaca0720 ]---

So there's at least another bug lurking..
Josh Poimboeuf June 24, 2016, 8:51 p.m. UTC | #2
On Fri, Jun 24, 2016 at 03:25:30PM -0500, Josh Poimboeuf wrote:
> On Fri, Jun 24, 2016 at 11:11:47AM -0700, Linus Torvalds wrote:
> > On Fri, Jun 24, 2016 at 10:51 AM, Linus Torvalds
> > <torvalds@linux-foundation.org> wrote:
> > >
> > > And in particular, the init_task stack initialization initialized it
> > > to the init_thread pointer. Which was definitely deadly.
> > >
> > > Let's see if that was it..
> > 
> > No, it's still broken. But it's *less* broken, so here's a new version
> > of the patch that at least gets some of the stack setup right, in my
> > hope that somebody will bother to look at this, and being less broken
> > might mean that somebody sees what else I missed..
> 
> I found at least one bug.  The changing of task->stack from a "void *" to an
> "unsigned long *":
> 
> > -	void *stack;
> > +	unsigned long *stack;
> 
> That subtly changes the pointer arithmetic in do_boot_cpu():
> 
> 
> 	idle->thread.sp = (unsigned long) (((struct pt_regs *)
> 			  (THREAD_SIZE +  task_stack_page(idle))) - 1);
> 
> 
> That ends up adding 128k to the stack page bottom instead of 16k.
> 
> But fixing that doesn't seem to fix this:
> 
> [18446743832.576241] ------------[ cut here ]------------
> [18446743832.576241] WARNING: CPU: 1 PID: 0 at /home/jpoimboe/git/linux/arch/x86/kernel/cpu/common.c:1434 cpu_init+0x34b/0x440
> [18446743832.576241] Modules linked in:
> [18446743832.576241] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.7.0-rc4+ #47
> [18446743832.576241] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.1-20150318_183358- 04/01/2014
> [18446743832.576241]  0000000000000086 574e5e6c6855ace9 ffff88007c553e88 ffffffff8143cb83
> [18446743832.576241]  0000000000000000 0000000000000000 ffff88007c553ec8 ffffffff810b0e7b
> [18446743832.576241]  0000059a00000000 0000000000000000 0000000000000000 0000000000000000
> [18446743832.576241] Call Trace:
> [18446743832.576241]  [<ffffffff8143cb83>] dump_stack+0x85/0xc2
> [18446743832.576241]  [<ffffffff810b0e7b>] __warn+0xcb/0xf0
> [18446743832.576241]  [<ffffffff810b0fad>] warn_slowpath_null+0x1d/0x20
> [18446743832.576241]  [<ffffffff810491bb>] cpu_init+0x34b/0x440
> [18446743832.576241]  [<ffffffff8105ab7c>] start_secondary+0x1c/0x1a0
> [18446743832.576241] ---[ end trace 924d57afbaca0720 ]---
> 
> So there's at least another bug lurking..

Found another bug:

#define stack_smp_processor_id()					\
({								\
	struct thread_info *ti;						\
	__asm__("andq %%rsp,%0; ":"=r" (ti) : "0" (CURRENT_MASK));	\
	ti->cpu;							\
})

That macro is obviously no longer valid.

That seems to cause the above warning.  When trying to boot CPU 1,
cpu_init() calls the above macro which incorrectly returns 0.
Andy Lutomirski June 24, 2016, 8:53 p.m. UTC | #3
On Fri, Jun 24, 2016 at 1:51 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Fri, Jun 24, 2016 at 03:25:30PM -0500, Josh Poimboeuf wrote:
>> On Fri, Jun 24, 2016 at 11:11:47AM -0700, Linus Torvalds wrote:
>> > On Fri, Jun 24, 2016 at 10:51 AM, Linus Torvalds
>> > <torvalds@linux-foundation.org> wrote:
>> > >
>> > > And in particular, the init_task stack initialization initialized it
>> > > to the init_thread pointer. Which was definitely deadly.
>> > >
>> > > Let's see if that was it..
>> >
>> > No, it's still broken. But it's *less* broken, so here's a new version
>> > of the patch that at least gets some of the stack setup right, in my
>> > hope that somebody will bother to look at this, and being less broken
>> > might mean that somebody sees what else I missed..
>>
>> I found at least one bug.  The changing of task->stack from a "void *" to an
>> "unsigned long *":
>>
>> > -   void *stack;
>> > +   unsigned long *stack;
>>
>> That subtly changes the pointer arithmetic in do_boot_cpu():
>>
>>
>>       idle->thread.sp = (unsigned long) (((struct pt_regs *)
>>                         (THREAD_SIZE +  task_stack_page(idle))) - 1);
>>
>>
>> That ends up adding 128k to the stack page bottom instead of 16k.
>>
>> But fixing that doesn't seem to fix this:
>>
>> [18446743832.576241] ------------[ cut here ]------------
>> [18446743832.576241] WARNING: CPU: 1 PID: 0 at /home/jpoimboe/git/linux/arch/x86/kernel/cpu/common.c:1434 cpu_init+0x34b/0x440
>> [18446743832.576241] Modules linked in:
>> [18446743832.576241] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.7.0-rc4+ #47
>> [18446743832.576241] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.8.1-20150318_183358- 04/01/2014
>> [18446743832.576241]  0000000000000086 574e5e6c6855ace9 ffff88007c553e88 ffffffff8143cb83
>> [18446743832.576241]  0000000000000000 0000000000000000 ffff88007c553ec8 ffffffff810b0e7b
>> [18446743832.576241]  0000059a00000000 0000000000000000 0000000000000000 0000000000000000
>> [18446743832.576241] Call Trace:
>> [18446743832.576241]  [<ffffffff8143cb83>] dump_stack+0x85/0xc2
>> [18446743832.576241]  [<ffffffff810b0e7b>] __warn+0xcb/0xf0
>> [18446743832.576241]  [<ffffffff810b0fad>] warn_slowpath_null+0x1d/0x20
>> [18446743832.576241]  [<ffffffff810491bb>] cpu_init+0x34b/0x440
>> [18446743832.576241]  [<ffffffff8105ab7c>] start_secondary+0x1c/0x1a0
>> [18446743832.576241] ---[ end trace 924d57afbaca0720 ]---
>>
>> So there's at least another bug lurking..
>
> Found another bug:
>
> #define stack_smp_processor_id()                                        \
> ({                                                              \
>         struct thread_info *ti;                                         \
>         __asm__("andq %%rsp,%0; ":"=r" (ti) : "0" (CURRENT_MASK));      \
>         ti->cpu;                                                        \
> })
>
> That macro is obviously no longer valid.
>
> That seems to cause the above warning.  When trying to boot CPU 1,
> cpu_init() calls the above macro which incorrectly returns 0.

Fixed in my queue by removing the function:

https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/commit/?h=x86/vmap_stack&id=01b1a4b6fd629820625b64ca6e17c987f2ee8c09

Patch
diff mbox

diff --git a/arch/mn10300/include/asm/thread_info.h b/arch/mn10300/include/asm/thread_info.h
index 4861a78c7160..f5f90bbf019d 100644
--- a/arch/mn10300/include/asm/thread_info.h
+++ b/arch/mn10300/include/asm/thread_info.h
@@ -115,7 +115,7 @@  static inline unsigned long current_stack_pointer(void)
 }
 
 #ifndef CONFIG_KGDB
-void arch_release_thread_info(struct thread_info *ti);
+void arch_release_thread_stack(unsigned long *stack);
 #endif
 #define get_thread_info(ti)	get_task_struct((ti)->task)
 #define put_thread_info(ti)	put_task_struct((ti)->task)
diff --git a/arch/mn10300/kernel/kgdb.c b/arch/mn10300/kernel/kgdb.c
index 99770823451a..2d7986c386fe 100644
--- a/arch/mn10300/kernel/kgdb.c
+++ b/arch/mn10300/kernel/kgdb.c
@@ -397,8 +397,9 @@  static bool kgdb_arch_undo_singlestep(struct pt_regs *regs)
  * single-step state is cleared.  At this point the breakpoints should have
  * been removed by __switch_to().
  */
-void arch_release_thread_info(struct thread_info *ti)
+void arch_release_thread_stack(unsigned long *stack)
 {
+	struct thread_info *ti = (void *)stack;
 	if (kgdb_sstep_thread == ti) {
 		kgdb_sstep_thread = NULL;
 
diff --git a/arch/tile/include/asm/thread_info.h b/arch/tile/include/asm/thread_info.h
index 4b7cef9e94e0..c1467ac59ce6 100644
--- a/arch/tile/include/asm/thread_info.h
+++ b/arch/tile/include/asm/thread_info.h
@@ -78,7 +78,7 @@  struct thread_info {
 
 #ifndef __ASSEMBLY__
 
-void arch_release_thread_info(struct thread_info *info);
+void arch_release_thread_stack(unsigned long *stack);
 
 /* How to get the thread information struct from C. */
 register unsigned long stack_pointer __asm__("sp");
diff --git a/arch/tile/kernel/process.c b/arch/tile/kernel/process.c
index 6b705ccc9cc1..a465d8372edd 100644
--- a/arch/tile/kernel/process.c
+++ b/arch/tile/kernel/process.c
@@ -73,8 +73,9 @@  void arch_cpu_idle(void)
 /*
  * Release a thread_info structure
  */
-void arch_release_thread_info(struct thread_info *info)
+void arch_release_thread_stack(unsigned long *stack)
 {
+	struct thread_info *info = (void *)stack;
 	struct single_step_state *step_state = info->step_state;
 
 	if (step_state) {
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index d9a94da0c29f..f33bc80577c5 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -154,6 +154,7 @@  config X86
 	select SPARSE_IRQ
 	select SRCU
 	select SYSCTL_EXCEPTION_TRACE
+	select THREAD_INFO_IN_TASK
 	select USER_STACKTRACE_SUPPORT
 	select VIRT_TO_BUS
 	select X86_DEV_DMA_OPS			if X86_64
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index ec138e538c44..d5feac5f252d 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -31,13 +31,6 @@ 
 #define CREATE_TRACE_POINTS
 #include <trace/events/syscalls.h>
 
-static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs)
-{
-	unsigned long top_of_stack =
-		(unsigned long)(regs + 1) + TOP_OF_KERNEL_STACK_PADDING;
-	return (struct thread_info *)(top_of_stack - THREAD_SIZE);
-}
-
 #ifdef CONFIG_CONTEXT_TRACKING
 /* Called on entry from user mode with IRQs off. */
 __visible void enter_from_user_mode(void)
@@ -78,7 +71,7 @@  static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)
  */
 unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
 {
-	struct thread_info *ti = pt_regs_to_thread_info(regs);
+	struct thread_info *ti = current_thread_info();
 	unsigned long ret = 0;
 	u32 work;
 
@@ -156,7 +149,7 @@  unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch)
 long syscall_trace_enter_phase2(struct pt_regs *regs, u32 arch,
 				unsigned long phase1_result)
 {
-	struct thread_info *ti = pt_regs_to_thread_info(regs);
+	struct thread_info *ti = current_thread_info();
 	long ret = 0;
 	u32 work = ACCESS_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY;
 
@@ -239,7 +232,7 @@  static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 		/* Disable IRQs and retry */
 		local_irq_disable();
 
-		cached_flags = READ_ONCE(pt_regs_to_thread_info(regs)->flags);
+		cached_flags = READ_ONCE(current_thread_info()->flags);
 
 		if (!(cached_flags & EXIT_TO_USERMODE_LOOP_FLAGS))
 			break;
@@ -250,7 +243,7 @@  static void exit_to_usermode_loop(struct pt_regs *regs, u32 cached_flags)
 /* Called with IRQs disabled. */
 __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
 {
-	struct thread_info *ti = pt_regs_to_thread_info(regs);
+	struct thread_info *ti = current_thread_info();
 	u32 cached_flags;
 
 	if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
@@ -309,7 +302,7 @@  static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
  */
 __visible inline void syscall_return_slowpath(struct pt_regs *regs)
 {
-	struct thread_info *ti = pt_regs_to_thread_info(regs);
+	struct thread_info *ti = current_thread_info();
 	u32 cached_flags = READ_ONCE(ti->flags);
 
 	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
@@ -332,7 +325,7 @@  __visible inline void syscall_return_slowpath(struct pt_regs *regs)
 #ifdef CONFIG_X86_64
 __visible void do_syscall_64(struct pt_regs *regs)
 {
-	struct thread_info *ti = pt_regs_to_thread_info(regs);
+	struct thread_info *ti = current_thread_info();
 	unsigned long nr = regs->orig_ax;
 
 	enter_from_user_mode();
@@ -365,7 +358,7 @@  __visible void do_syscall_64(struct pt_regs *regs)
  */
 static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
 {
-	struct thread_info *ti = pt_regs_to_thread_info(regs);
+	struct thread_info *ti = current_thread_info();
 	unsigned int nr = (unsigned int)regs->orig_ax;
 
 #ifdef CONFIG_IA32_EMULATION
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 9ee0da1807ed..f49742de2c65 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -179,7 +179,8 @@  GLOBAL(entry_SYSCALL_64_after_swapgs)
 	 * If we need to do entry work or if we guess we'll need to do
 	 * exit work, go straight to the slow path.
 	 */
-	testl	$_TIF_WORK_SYSCALL_ENTRY|_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
+	GET_THREAD_INFO(%r11)
+	testl	$_TIF_WORK_SYSCALL_ENTRY|_TIF_ALLWORK_MASK, TI_flags(%r11)
 	jnz	entry_SYSCALL64_slow_path
 
 entry_SYSCALL_64_fastpath:
@@ -217,7 +218,8 @@  entry_SYSCALL_64_fastpath:
 	 */
 	DISABLE_INTERRUPTS(CLBR_NONE)
 	TRACE_IRQS_OFF
-	testl	$_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
+	GET_THREAD_INFO(%r11)
+	testl	$_TIF_ALLWORK_MASK, TI_flags(%r11)
 	jnz	1f
 
 	LOCKDEP_SYS_EXIT
@@ -368,9 +370,10 @@  END(ptregs_\func)
  * A newly forked process directly context switches into this address.
  *
  * rdi: prev task we switched from
+ * rsi: task we're switching to
  */
 ENTRY(ret_from_fork)
-	LOCK ; btr $TIF_FORK, TI_flags(%r8)
+	LOCK ; btr $TIF_FORK, TI_flags(%rsi)	/* rsi: this newly forked task */
 
 	call	schedule_tail			/* rdi: 'prev' task parameter */
 
diff --git a/arch/x86/include/asm/kprobes.h b/arch/x86/include/asm/kprobes.h
index 4421b5da409d..1d2997e74b08 100644
--- a/arch/x86/include/asm/kprobes.h
+++ b/arch/x86/include/asm/kprobes.h
@@ -38,12 +38,12 @@  typedef u8 kprobe_opcode_t;
 #define RELATIVECALL_OPCODE 0xe8
 #define RELATIVE_ADDR_SIZE 4
 #define MAX_STACK_SIZE 64
-#define MIN_STACK_SIZE(ADDR)					       \
-	(((MAX_STACK_SIZE) < (((unsigned long)current_thread_info()) + \
-			      THREAD_SIZE - (unsigned long)(ADDR)))    \
-	 ? (MAX_STACK_SIZE)					       \
-	 : (((unsigned long)current_thread_info()) +		       \
-	    THREAD_SIZE - (unsigned long)(ADDR)))
+
+#define current_stack_top() ((unsigned long)task_stack_page(current)+THREAD_SIZE)
+#define current_stack_size(ADDR) (current_stack_top() - (unsigned long)(ADDR))
+
+#define MIN_STACK_SIZE(ADDR) \
+	(MAX_STACK_SIZE < current_stack_size(ADDR) ? MAX_STACK_SIZE : current_stack_size(ADDR))
 
 #define flush_insn_slot(p)	do { } while (0)
 
diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index 8f321a1b03a1..ae0aa0612c67 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -110,18 +110,16 @@  do {									\
 	     "call __switch_to\n\t"					  \
 	     "movq "__percpu_arg([current_task])",%%rsi\n\t"		  \
 	     __switch_canary						  \
-	     "movq %P[thread_info](%%rsi),%%r8\n\t"			  \
 	     "movq %%rax,%%rdi\n\t" 					  \
-	     "testl  %[_tif_fork],%P[ti_flags](%%r8)\n\t"		  \
+	     "testl  %[_tif_fork],%P[ti_flags](%%rsi)\n\t"		  \
 	     "jnz   ret_from_fork\n\t"					  \
 	     RESTORE_CONTEXT						  \
 	     : "=a" (last)					  	  \
 	       __switch_canary_oparam					  \
 	     : [next] "S" (next), [prev] "D" (prev),			  \
 	       [threadrsp] "i" (offsetof(struct task_struct, thread.sp)), \
-	       [ti_flags] "i" (offsetof(struct thread_info, flags)),	  \
+	       [ti_flags] "i" (offsetof(struct task_struct, thread_info.flags)),	  \
 	       [_tif_fork] "i" (_TIF_FORK),			  	  \
-	       [thread_info] "i" (offsetof(struct task_struct, stack)),   \
 	       [current_task] "m" (current_task)			  \
 	       __switch_canary_iparam					  \
 	     : "memory", "cc" __EXTRA_CLOBBER)
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 30c133ac05cd..d38ebb08f4c1 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -53,24 +53,21 @@  struct task_struct;
 #include <linux/atomic.h>
 
 struct thread_info {
-	struct task_struct	*task;		/* main task structure */
 	__u32			flags;		/* low level flags */
 	__u32			status;		/* thread synchronous flags */
 	__u32			cpu;		/* current CPU */
-	mm_segment_t		addr_limit;
 	unsigned int		sig_on_uaccess_error:1;
 	unsigned int		uaccess_err:1;	/* uaccess failed */
+	mm_segment_t		addr_limit;
 };
 
 #define INIT_THREAD_INFO(tsk)			\
 {						\
-	.task		= &tsk,			\
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.addr_limit	= KERNEL_DS,		\
 }
 
-#define init_thread_info	(init_thread_union.thread_info)
 #define init_stack		(init_thread_union.stack)
 
 #else /* !__ASSEMBLY__ */
@@ -166,7 +163,7 @@  struct thread_info {
 
 static inline struct thread_info *current_thread_info(void)
 {
-	return (struct thread_info *)(current_top_of_stack() - THREAD_SIZE);
+	return (struct thread_info *)current;
 }
 
 static inline unsigned long current_stack_pointer(void)
@@ -188,35 +185,7 @@  static inline unsigned long current_stack_pointer(void)
 
 /* Load thread_info address into "reg" */
 #define GET_THREAD_INFO(reg) \
-	_ASM_MOV PER_CPU_VAR(cpu_current_top_of_stack),reg ; \
-	_ASM_SUB $(THREAD_SIZE),reg ;
-
-/*
- * ASM operand which evaluates to a 'thread_info' address of
- * the current task, if it is known that "reg" is exactly "off"
- * bytes below the top of the stack currently.
- *
- * ( The kernel stack's size is known at build time, it is usually
- *   2 or 4 pages, and the bottom  of the kernel stack contains
- *   the thread_info structure. So to access the thread_info very
- *   quickly from assembly code we can calculate down from the
- *   top of the kernel stack to the bottom, using constant,
- *   build-time calculations only. )
- *
- * For example, to fetch the current thread_info->flags value into %eax
- * on x86-64 defconfig kernels, in syscall entry code where RSP is
- * currently at exactly SIZEOF_PTREGS bytes away from the top of the
- * stack:
- *
- *      mov ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS), %eax
- *
- * will translate to:
- *
- *      8b 84 24 b8 c0 ff ff      mov    -0x3f48(%rsp), %eax
- *
- * which is below the current RSP by almost 16K.
- */
-#define ASM_THREAD_INFO(field, reg, off) ((field)+(off)-THREAD_SIZE)(reg)
+	_ASM_MOV PER_CPU_VAR(current_task),reg
 
 #endif
 
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index d6209f3a69cb..ef8017ca5ba9 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -80,7 +80,7 @@  print_ftrace_graph_addr(unsigned long addr, void *data,
 static inline int valid_stack_ptr(struct task_struct *task,
 			void *p, unsigned int size, void *end)
 {
-	void *t = task_thread_info(task);
+	void *t = task_stack_page(task);
 	if (end) {
 		if (p < end && p >= (end-THREAD_SIZE))
 			return 1;
diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c
index 38da8f29a9c8..c627bf8d98ad 100644
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -130,11 +130,9 @@  void irq_ctx_init(int cpu)
 
 void do_softirq_own_stack(void)
 {
-	struct thread_info *curstk;
 	struct irq_stack *irqstk;
 	u32 *isp, *prev_esp;
 
-	curstk = current_stack();
 	irqstk = __this_cpu_read(softirq_stack);
 
 	/* build the stack frame on the softirq stack */
diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
index 206d0b90a3ab..38f9f5678dc8 100644
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -41,8 +41,7 @@  static inline void stack_overflow_check(struct pt_regs *regs)
 	if (user_mode(regs))
 		return;
 
-	if (regs->sp >= curbase + sizeof(struct thread_info) +
-				  sizeof(struct pt_regs) + STACK_TOP_MARGIN &&
+	if (regs->sp >= curbase + sizeof(struct pt_regs) + STACK_TOP_MARGIN &&
 	    regs->sp <= curbase + THREAD_SIZE)
 		return;
 
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 96becbbb52e0..8f60f810a9e7 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -536,9 +536,7 @@  unsigned long get_wchan(struct task_struct *p)
 	 * PADDING
 	 * ----------- top = topmax - TOP_OF_KERNEL_STACK_PADDING
 	 * stack
-	 * ----------- bottom = start + sizeof(thread_info)
-	 * thread_info
-	 * ----------- start
+	 * ----------- bottom = start
 	 *
 	 * The tasks stack pointer points at the location where the
 	 * framepointer is stored. The data on the stack is:
@@ -549,7 +547,7 @@  unsigned long get_wchan(struct task_struct *p)
 	 */
 	top = start + THREAD_SIZE - TOP_OF_KERNEL_STACK_PADDING;
 	top -= 2 * sizeof(unsigned long);
-	bottom = start + sizeof(struct thread_info);
+	bottom = start;
 
 	sp = READ_ONCE(p->thread.sp);
 	if (sp < bottom || sp > top)
diff --git a/arch/x86/um/ptrace_32.c b/arch/x86/um/ptrace_32.c
index ebd4dd6ef73b..14e8f6a628c2 100644
--- a/arch/x86/um/ptrace_32.c
+++ b/arch/x86/um/ptrace_32.c
@@ -191,7 +191,7 @@  int peek_user(struct task_struct *child, long addr, long data)
 
 static int get_fpregs(struct user_i387_struct __user *buf, struct task_struct *child)
 {
-	int err, n, cpu = ((struct thread_info *) child->stack)->cpu;
+	int err, n, cpu = task_thread_info(child)->cpu;
 	struct user_i387_struct fpregs;
 
 	err = save_i387_registers(userspace_pid[cpu],
@@ -208,7 +208,7 @@  static int get_fpregs(struct user_i387_struct __user *buf, struct task_struct *c
 
 static int set_fpregs(struct user_i387_struct __user *buf, struct task_struct *child)
 {
-	int n, cpu = ((struct thread_info *) child->stack)->cpu;
+	int n, cpu = task_thread_info(child)->cpu;
 	struct user_i387_struct fpregs;
 
 	n = copy_from_user(&fpregs, buf, sizeof(fpregs));
@@ -221,7 +221,7 @@  static int set_fpregs(struct user_i387_struct __user *buf, struct task_struct *c
 
 static int get_fpxregs(struct user_fxsr_struct __user *buf, struct task_struct *child)
 {
-	int err, n, cpu = ((struct thread_info *) child->stack)->cpu;
+	int err, n, cpu = task_thread_info(child)->cpu;
 	struct user_fxsr_struct fpregs;
 
 	err = save_fpx_registers(userspace_pid[cpu], (unsigned long *) &fpregs);
@@ -237,7 +237,7 @@  static int get_fpxregs(struct user_fxsr_struct __user *buf, struct task_struct *
 
 static int set_fpxregs(struct user_fxsr_struct __user *buf, struct task_struct *child)
 {
-	int n, cpu = ((struct thread_info *) child->stack)->cpu;
+	int n, cpu = task_thread_info(child)->cpu;
 	struct user_fxsr_struct fpregs;
 
 	n = copy_from_user(&fpregs, buf, sizeof(fpregs));
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index f2cb8d45513d..9c04d44eeb3c 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -15,6 +15,8 @@ 
 #include <net/net_namespace.h>
 #include <linux/sched/rt.h>
 
+#include <asm/thread_info.h>
+
 #ifdef CONFIG_SMP
 # define INIT_PUSHABLE_TASKS(tsk)					\
 	.pushable_tasks = PLIST_NODE_INIT(tsk.pushable_tasks, MAX_PRIO),
@@ -183,14 +185,21 @@  extern struct task_group root_task_group;
 # define INIT_KASAN(tsk)
 #endif
 
+#ifdef CONFIG_THREAD_INFO_IN_TASK
+# define INIT_TASK_TI(tsk) .thread_info = INIT_THREAD_INFO(tsk),
+#else
+# define INIT_TASK_TI(tsk)
+#endif
+
 /*
  *  INIT_TASK is used to set up the first task table, touch at
  * your own risk!. Base=0, limit=0x1fffff (=2MB)
  */
 #define INIT_TASK(tsk)	\
 {									\
+	INIT_TASK_TI(tsk)						\
 	.state		= 0,						\
-	.stack		= &init_thread_info,				\
+	.stack		= init_stack,					\
 	.usage		= ATOMIC_INIT(2),				\
 	.flags		= PF_KTHREAD,					\
 	.prio		= MAX_PRIO-20,					\
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6e42ada26345..04aeb0c7b564 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1456,8 +1456,11 @@  struct tlbflush_unmap_batch {
 };
 
 struct task_struct {
+#ifdef CONFIG_THREAD_INFO_IN_TASK
+	struct thread_info thread_info;
+#endif
 	volatile long state;	/* -1 unrunnable, 0 runnable, >0 stopped */
-	void *stack;
+	unsigned long *stack;
 	atomic_t usage;
 	unsigned int flags;	/* per process flags, defined below */
 	unsigned int ptrace;
@@ -2539,7 +2542,9 @@  extern void set_curr_task(int cpu, struct task_struct *p);
 void yield(void);
 
 union thread_union {
+#ifndef CONFIG_THREAD_INFO_IN_TASK
 	struct thread_info thread_info;
+#endif
 	unsigned long stack[THREAD_SIZE/sizeof(long)];
 };
 
@@ -2967,7 +2972,14 @@  static inline void threadgroup_change_end(struct task_struct *tsk)
 	cgroup_threadgroup_change_end(tsk);
 }
 
-#ifndef __HAVE_THREAD_FUNCTIONS
+#ifdef CONFIG_THREAD_INFO_IN_TASK
+
+#define task_thread_info(task)		(&(task)->thread_info)
+#define task_stack_page(task)		((task)->stack)
+#define setup_thread_stack(new,old)	do { } while(0)
+#define end_of_stack(task)		((unsigned long *)task_stack_page(task))
+
+#elif !defined(__HAVE_THREAD_FUNCTIONS)
 
 #define task_thread_info(task)	((struct thread_info *)(task)->stack)
 #define task_stack_page(task)	((task)->stack)
diff --git a/init/Kconfig b/init/Kconfig
index f755a602d4a1..0c83af6d3753 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -26,6 +26,9 @@  config IRQ_WORK
 config BUILDTIME_EXTABLE_SORT
 	bool
 
+config THREAD_INFO_IN_TASK
+	bool
+
 menu "General setup"
 
 config BROKEN
diff --git a/init/init_task.c b/init/init_task.c
index ba0a7f362d9e..11f83be1fa79 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -22,5 +22,8 @@  EXPORT_SYMBOL(init_task);
  * Initial thread structure. Alignment of this is handled by a special
  * linker map entry.
  */
-union thread_union init_thread_union __init_task_data =
-	{ INIT_THREAD_INFO(init_task) };
+union thread_union init_thread_union __init_task_data = {
+#ifndef CONFIG_THREAD_INFO_IN_TASK
+	INIT_THREAD_INFO(init_task)
+#endif
+};
diff --git a/kernel/fork.c b/kernel/fork.c
index 5c2c355aa97f..9f290226d9d5 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -148,7 +148,7 @@  static inline void free_task_struct(struct task_struct *tsk)
 }
 #endif
 
-void __weak arch_release_thread_info(struct thread_info *ti)
+void __weak arch_release_thread_stack(unsigned long *stack)
 {
 }
 
@@ -159,7 +159,7 @@  void __weak arch_release_thread_info(struct thread_info *ti)
  * kmemcache based allocator.
  */
 # if THREAD_SIZE >= PAGE_SIZE
-static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
+static unsigned long *alloc_thread_stack_node(struct task_struct *tsk,
 						  int node)
 {
 	struct page *page = alloc_kmem_pages_node(node, THREADINFO_GFP,
@@ -172,31 +172,31 @@  static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
 	return page ? page_address(page) : NULL;
 }
 
-static inline void free_thread_info(struct thread_info *ti)
+static inline void free_thread_stack(unsigned long *stack)
 {
-	struct page *page = virt_to_page(ti);
+	struct page *page = virt_to_page(stack);
 
 	memcg_kmem_update_page_stat(page, MEMCG_KERNEL_STACK,
 				    -(1 << THREAD_SIZE_ORDER));
 	__free_kmem_pages(page, THREAD_SIZE_ORDER);
 }
 # else
-static struct kmem_cache *thread_info_cache;
+static struct kmem_cache *thread_stack_cache;
 
-static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
+static struct thread_info *alloc_thread_stack_node(struct task_struct *tsk,
 						  int node)
 {
-	return kmem_cache_alloc_node(thread_info_cache, THREADINFO_GFP, node);
+	return kmem_cache_alloc_node(thread_stack_cache, THREADINFO_GFP, node);
 }
 
-static void free_thread_info(struct thread_info *ti)
+static void free_stack(unsigned long *stack)
 {
-	kmem_cache_free(thread_info_cache, ti);
+	kmem_cache_free(thread_stack_cache, stack);
 }
 
 void thread_info_cache_init(void)
 {
-	thread_info_cache = kmem_cache_create("thread_info", THREAD_SIZE,
+	thread_stack_cache = kmem_cache_create("thread_stack", THREAD_SIZE,
 					      THREAD_SIZE, 0, NULL);
 	BUG_ON(thread_info_cache == NULL);
 }
@@ -221,9 +221,9 @@  struct kmem_cache *vm_area_cachep;
 /* SLAB cache for mm_struct structures (tsk->mm) */
 static struct kmem_cache *mm_cachep;
 
-static void account_kernel_stack(struct thread_info *ti, int account)
+static void account_kernel_stack(unsigned long *stack, int account)
 {
-	struct zone *zone = page_zone(virt_to_page(ti));
+	struct zone *zone = page_zone(virt_to_page(stack));
 
 	mod_zone_page_state(zone, NR_KERNEL_STACK, account);
 }
@@ -231,8 +231,8 @@  static void account_kernel_stack(struct thread_info *ti, int account)
 void free_task(struct task_struct *tsk)
 {
 	account_kernel_stack(tsk->stack, -1);
-	arch_release_thread_info(tsk->stack);
-	free_thread_info(tsk->stack);
+	arch_release_thread_stack(tsk->stack);
+	free_thread_stack(tsk->stack);
 	rt_mutex_debug_task_free(tsk);
 	ftrace_graph_exit_task(tsk);
 	put_seccomp_filter(tsk);
@@ -343,7 +343,7 @@  void set_task_stack_end_magic(struct task_struct *tsk)
 static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 {
 	struct task_struct *tsk;
-	struct thread_info *ti;
+	unsigned long *stack;
 	int err;
 
 	if (node == NUMA_NO_NODE)
@@ -352,15 +352,15 @@  static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 	if (!tsk)
 		return NULL;
 
-	ti = alloc_thread_info_node(tsk, node);
-	if (!ti)
+	stack = alloc_thread_stack_node(tsk, node);
+	if (!stack)
 		goto free_tsk;
 
 	err = arch_dup_task_struct(tsk, orig);
 	if (err)
-		goto free_ti;
+		goto free_stack;
 
-	tsk->stack = ti;
+	tsk->stack = stack;
 #ifdef CONFIG_SECCOMP
 	/*
 	 * We must handle setting up seccomp filters once we're under
@@ -392,14 +392,14 @@  static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
 	tsk->task_frag.page = NULL;
 	tsk->wake_q.next = NULL;
 
-	account_kernel_stack(ti, 1);
+	account_kernel_stack(stack, 1);
 
 	kcov_task_init(tsk);
 
 	return tsk;
 
-free_ti:
-	free_thread_info(ti);
+free_stack:
+	free_thread_stack(stack);
 free_tsk:
 	free_task_struct(tsk);
 	return NULL;