Commit c02433dd authored by Mark Rutland's avatar Mark Rutland Committed by Catalin Marinas
Browse files

arm64: split thread_info from task stack 



This patch moves arm64's struct thread_info from the task stack into
task_struct. This protects thread_info from corruption in the case of
stack overflows, and makes its address harder to determine if stack
addresses are leaked, making a number of attacks more difficult. Precise
detection and handling of overflow is left for subsequent patches.

Largely, this involves changing code to store the task_struct in sp_el0,
and acquire the thread_info from the task struct. Core code now
implements current_thread_info(), and as noted in <linux/sched.h> this
relies on offsetof(task_struct, thread_info) == 0, enforced by core
code.

This change means that the 'tsk' register used in entry.S now points to
a task_struct, rather than a thread_info as it used to. To make this
clear, the TI_* field offsets are renamed to TSK_TI_*, with asm-offsets
appropriately updated to account for the structural change.

Userspace clobbers sp_el0, and we can no longer restore this from the
stack. Instead, the current task is cached in a per-cpu variable that we
can safely access from early assembly as interrupts are disabled (and we
are thus not preemptible).

Both secondary entry and idle are updated to stash the sp and task
pointer separately.

Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Tested-by: default avatarLaura Abbott <labbott@redhat.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: James Morse <james.morse@arm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 1b7e2296

arch/arm64/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -109,6 +109,7 @@ config ARM64 
	select POWER_SUPPLY

	select SPARSE_IRQ

	select SYSCTL_EXCEPTION_TRACE

	select THREAD_INFO_IN_TASK

	help

	  ARM 64-bit (AArch64) Linux support.

arch/arm64/include/asm/Kbuild

+0 −1
Original line number Diff line number Diff line 
generic-y += bugs.h

generic-y += clkdev.h

generic-y += cputime.h

generic-y += current.h

generic-y += delay.h

generic-y += div64.h

generic-y += dma.h

arch/arm64/include/asm/current.h

0 → 100644
+22 −0
Original line number Diff line number Diff line 
#ifndef __ASM_CURRENT_H

#define __ASM_CURRENT_H



#include <linux/compiler.h>



#include <asm/sysreg.h>



#ifndef __ASSEMBLY__



struct task_struct;



static __always_inline struct task_struct *get_current(void)

{

	return (struct task_struct *)read_sysreg(sp_el0);

}



#define current get_current()



#endif /* __ASSEMBLY__ */



#endif /* __ASM_CURRENT_H */

arch/arm64/include/asm/smp.h

+1 −0
Original line number Diff line number Diff line
@@ -82,6 +82,7 @@ asmlinkage void secondary_start_kernel(void); 
 */

struct secondary_data {

	void *stack;

	struct task_struct *task;

	long status;

};

arch/arm64/include/asm/thread_info.h

+0 −24
Original line number Diff line number Diff line
@@ -47,41 +47,17 @@ typedef unsigned long mm_segment_t; 
struct thread_info {

	unsigned long		flags;		/* low level flags */

	mm_segment_t		addr_limit;	/* address limit */

	struct task_struct	*task;		/* main task structure */

	int			preempt_count;	/* 0 => preemptable, <0 => bug */

	int			cpu;		/* cpu */

};



#define INIT_THREAD_INFO(tsk)						\

{									\

	.task		= &tsk,						\

	.flags		= 0,						\

	.preempt_count	= INIT_PREEMPT_COUNT,				\

	.addr_limit	= KERNEL_DS,					\

}



#define init_stack		(init_thread_union.stack)



/*

 * how to get the thread information struct from C

 */

static inline struct thread_info *current_thread_info(void) __attribute_const__;



/*

 * struct thread_info can be accessed directly via sp_el0.

 *

 * We don't use read_sysreg() as we want the compiler to cache the value where

 * possible.

 */

static inline struct thread_info *current_thread_info(void)

{

	unsigned long sp_el0;



	asm ("mrs %0, sp_el0" : "=r" (sp_el0));



	return (struct thread_info *)sp_el0;

}



#define thread_saved_pc(tsk)	\

	((unsigned long)(tsk->thread.cpu_context.pc))

#define thread_saved_sp(tsk)	\

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