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Commit 3ec83365 authored by Mark Rutland's avatar Mark Rutland Committed by Gerrit - the friendly Code Review server
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BACKPORT: 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>

This is a modification of Mark Rutland's original patch. Guards to check
if CONFIG_THREAD_INFO_IN_TASK is used has been inserted. get_current()
for when CONFIG_THREAD_INFO_IN_TASK is not used has been added to
arch/arm64/include/asm/current.h.

Bug: 64672701
Change-Id: Ic5eae344a7c2baea0864f6ae16be1e9c60c0a74a
(cherry picked from commit c02433dd6de32f042cf3ffe476746b1115b8c096)
Signed-off-by: default avatarZubin Mithra <zsm@google.com>
Git-repo: https://android.googlesource.com/kernel/msm


Git-commit: fe5800b60e30df67caed77da246150c8d478538b
Signed-off-by: default avatarChetan C R <cravin@codeaurora.org>
parent 9f52526c

arch/arm64/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -85,6 +85,7 @@ config ARM64 
	select SPARSE_IRQ

	select SYSCTL_EXCEPTION_TRACE

	select HAVE_CONTEXT_TRACKING

	select THREAD_INFO_IN_TASK

	select MSM_JTAGV8 if CORESIGHT_ETMV4

	help

	  ARM 64-bit (AArch64) Linux support.

arch/arm64/include/asm/current.h

0 → 100644
+27 −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__



#ifdef CONFIG_THREAD_INFO_IN_TASK

struct task_struct;



static __always_inline struct task_struct *get_current(void)

{

	return (struct task_struct *)read_sysreg(sp_el0);

}

#define current get_current()

#else

#include <linux/thread_info.h>

#define get_current() (current_thread_info()->task)

#define current get_current()

#endif



#endif /* __ASSEMBLY__ */



#endif /* __ASM_CURRENT_H */

arch/arm64/include/asm/smp.h

+3 −0
Original line number Diff line number Diff line
@@ -56,6 +56,9 @@ asmlinkage void secondary_start_kernel(void); 
 */

struct secondary_data {

	void *stack;

#ifdef CONFIG_THREAD_INFO_IN_TASK

	struct task_struct *task;

#endif

};

extern struct secondary_data secondary_data;

extern void secondary_entry(void);

arch/arm64/include/asm/thread_info.h

+14 −1
Original line number Diff line number Diff line
@@ -46,15 +46,26 @@ typedef unsigned long mm_segment_t; 
struct thread_info {

	unsigned long		flags;		/* low level flags */

	mm_segment_t		addr_limit;	/* address limit */

#ifndef CONFIG_THREAD_INFO_IN_TASK

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

#endif

	struct exec_domain	*exec_domain;	/* execution domain */

#ifdef CONFIG_ARM64_SW_TTBR0_PAN

	u64			ttbr0;		/* saved TTBR0_EL1 */

#endif

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

#ifndef CONFIG_THREAD_INFO_IN_TASK

	int			cpu;		/* cpu */

#endif

};



#ifdef CONFIG_THREAD_INFO_IN_TASK

#define INIT_THREAD_INFO(tsk)						\

{									\

	.preempt_count	= INIT_PREEMPT_COUNT,				\

	.addr_limit	= KERNEL_DS,					\

}

#else

#define INIT_THREAD_INFO(tsk)						\

{									\

	.task		= &tsk,						\
@@ -65,7 +76,6 @@ struct thread_info { 
}



#define init_thread_info	(init_thread_union.thread_info)

#define init_stack		(init_thread_union.stack)



/*

 * how to get the current stack pointer from C
@@ -88,6 +98,9 @@ static inline struct thread_info *current_thread_info(void) 


	return (struct thread_info *)sp_el0;

}

#endif



#define init_stack		(init_thread_union.stack)



#define thread_saved_pc(tsk)	\

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

arch/arm64/kernel/asm-offsets.c

+12 −2
Original line number Diff line number Diff line
@@ -34,12 +34,17 @@ int main(void) 
{

  DEFINE(TSK_ACTIVE_MM,		offsetof(struct task_struct, active_mm));

  BLANK();

#ifdef CONFIG_THREAD_INFO_IN_TASK

  DEFINE(TSK_TI_FLAGS,		offsetof(struct task_struct, thread_info.flags));

  DEFINE(TSK_TI_PREEMPT,	offsetof(struct task_struct, thread_info.preempt_count));

  DEFINE(TSK_TI_ADDR_LIMIT,	offsetof(struct task_struct, thread_info.addr_limit));

  DEFINE(TSK_STACK,		offsetof(struct task_struct, stack));

#else

  DEFINE(TI_FLAGS,		offsetof(struct thread_info, flags));

  DEFINE(TI_PREEMPT,		offsetof(struct thread_info, preempt_count));

  DEFINE(TI_ADDR_LIMIT,		offsetof(struct thread_info, addr_limit));

  DEFINE(TI_TASK,		offsetof(struct thread_info, task));

  DEFINE(TI_EXEC_DOMAIN,	offsetof(struct thread_info, exec_domain));

  DEFINE(TI_CPU,		offsetof(struct thread_info, cpu));

#endif

#ifdef CONFIG_ARM64_SW_TTBR0_PAN

  DEFINE(TSK_TI_TTBR0,		offsetof(struct thread_info, ttbr0));

#endif
@@ -113,6 +118,11 @@ int main(void) 
  DEFINE(TZ_MINWEST,		offsetof(struct timezone, tz_minuteswest));

  DEFINE(TZ_DSTTIME,		offsetof(struct timezone, tz_dsttime));

  BLANK();

#ifdef CONFIG_THREAD_INFO_IN_TASK

  DEFINE(CPU_BOOT_STACK,	offsetof(struct secondary_data, stack));

  DEFINE(CPU_BOOT_TASK,		offsetof(struct secondary_data, task));

  BLANK();

#endif

#ifdef CONFIG_KVM_ARM_HOST

  DEFINE(VCPU_CONTEXT,		offsetof(struct kvm_vcpu, arch.ctxt));

  DEFINE(CPU_GP_REGS,		offsetof(struct kvm_cpu_context, gp_regs));