Commit 8f159f1d authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

x86/entry/common: Protect against instrumentation 



Mark the various syscall entries with noinstr to protect them against
instrumentation and add the noinstrumentation_begin()/end() annotations to mark the
parts of the functions which are safe to call out into instrumentable code.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarAlexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200505134340.520277507@linutronix.de
parent 1723be30

arch/x86/entry/common.c

+89 −44
Original line number Diff line number Diff line
@@ -41,15 +41,26 @@ 


#ifdef CONFIG_CONTEXT_TRACKING

/* Called on entry from user mode with IRQs off. */

__visible inline noinstr void enter_from_user_mode(void)

__visible noinstr void enter_from_user_mode(void)

{

	CT_WARN_ON(ct_state() != CONTEXT_USER);

	enum ctx_state state = ct_state();



	user_exit_irqoff();



	instrumentation_begin();

	CT_WARN_ON(state != CONTEXT_USER);

	instrumentation_end();

}

#else

static inline void enter_from_user_mode(void) {}

#endif



static noinstr void exit_to_user_mode(void)

{

	user_enter_irqoff();

	mds_user_clear_cpu_buffers();

}



static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch)

{

#ifdef CONFIG_X86_64
@@ -179,8 +190,7 @@ 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)

static void __prepare_exit_to_usermode(struct pt_regs *regs)

{

	struct thread_info *ti = current_thread_info();

	u32 cached_flags;
@@ -219,10 +229,14 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs) 
	 */

	ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED);

#endif

}



	user_enter_irqoff();



	mds_user_clear_cpu_buffers();

__visible noinstr void prepare_exit_to_usermode(struct pt_regs *regs)

{

	instrumentation_begin();

	__prepare_exit_to_usermode(regs);

	instrumentation_end();

	exit_to_user_mode();

}



#define SYSCALL_EXIT_WORK_FLAGS				\
@@ -251,11 +265,7 @@ static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags) 
		tracehook_report_syscall_exit(regs, step);

}



/*

 * Called with IRQs on and fully valid regs.  Returns with IRQs off in a

 * state such that we can immediately switch to user mode.

 */

__visible inline void syscall_return_slowpath(struct pt_regs *regs)

static void __syscall_return_slowpath(struct pt_regs *regs)

{

	struct thread_info *ti = current_thread_info();

	u32 cached_flags = READ_ONCE(ti->flags);
@@ -276,15 +286,29 @@ __visible inline void syscall_return_slowpath(struct pt_regs *regs) 
		syscall_slow_exit_work(regs, cached_flags);



	local_irq_disable();

	prepare_exit_to_usermode(regs);

	__prepare_exit_to_usermode(regs);

}



/*

 * Called with IRQs on and fully valid regs.  Returns with IRQs off in a

 * state such that we can immediately switch to user mode.

 */

__visible noinstr void syscall_return_slowpath(struct pt_regs *regs)

{

	instrumentation_begin();

	__syscall_return_slowpath(regs);

	instrumentation_end();

	exit_to_user_mode();

}



#ifdef CONFIG_X86_64

__visible void do_syscall_64(unsigned long nr, struct pt_regs *regs)

__visible noinstr void do_syscall_64(unsigned long nr, struct pt_regs *regs)

{

	struct thread_info *ti;



	enter_from_user_mode();

	instrumentation_begin();



	local_irq_enable();

	ti = current_thread_info();

	if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
@@ -301,8 +325,10 @@ __visible void do_syscall_64(unsigned long nr, struct pt_regs *regs) 
		regs->ax = x32_sys_call_table[nr](regs);

#endif

	}

	__syscall_return_slowpath(regs);



	syscall_return_slowpath(regs);

	instrumentation_end();

	exit_to_user_mode();

}

#endif
@@ -313,7 +339,7 @@ __visible void do_syscall_64(unsigned long nr, struct pt_regs *regs) 
 * extremely hot in workloads that use it, and it's usually called from

 * do_fast_syscall_32, so forcibly inline it to improve performance.

 */

static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)

static void do_syscall_32_irqs_on(struct pt_regs *regs)

{

	struct thread_info *ti = current_thread_info();

	unsigned int nr = (unsigned int)regs->orig_ax;
@@ -337,27 +363,62 @@ static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs) 
		regs->ax = ia32_sys_call_table[nr](regs);

	}



	syscall_return_slowpath(regs);

	__syscall_return_slowpath(regs);

}



/* Handles int $0x80 */

__visible void do_int80_syscall_32(struct pt_regs *regs)

__visible noinstr void do_int80_syscall_32(struct pt_regs *regs)

{

	enter_from_user_mode();

	instrumentation_begin();



	local_irq_enable();

	do_syscall_32_irqs_on(regs);



	instrumentation_end();

	exit_to_user_mode();

}



static bool __do_fast_syscall_32(struct pt_regs *regs)

{

	int res;



	/* Fetch EBP from where the vDSO stashed it. */

	if (IS_ENABLED(CONFIG_X86_64)) {

		/*

		 * Micro-optimization: the pointer we're following is

		 * explicitly 32 bits, so it can't be out of range.

		 */

		res = __get_user(*(u32 *)&regs->bp,

			 (u32 __user __force *)(unsigned long)(u32)regs->sp);

	} else {

		res = get_user(*(u32 *)&regs->bp,

		       (u32 __user __force *)(unsigned long)(u32)regs->sp);

	}



	if (res) {

		/* User code screwed up. */

		regs->ax = -EFAULT;

		local_irq_disable();

		__prepare_exit_to_usermode(regs);

		return false;

	}



	/* Now this is just like a normal syscall. */

	do_syscall_32_irqs_on(regs);

	return true;

}



/* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */

__visible long do_fast_syscall_32(struct pt_regs *regs)

__visible noinstr long do_fast_syscall_32(struct pt_regs *regs)

{

	/*

	 * Called using the internal vDSO SYSENTER/SYSCALL32 calling

	 * convention.  Adjust regs so it looks like we entered using int80.

	 */



	unsigned long landing_pad = (unsigned long)current->mm->context.vdso +

					vdso_image_32.sym_int80_landing_pad;

	bool success;



	/*

	 * SYSENTER loses EIP, and even SYSCALL32 needs us to skip forward
@@ -367,33 +428,17 @@ __visible long do_fast_syscall_32(struct pt_regs *regs) 
	regs->ip = landing_pad;



	enter_from_user_mode();

	instrumentation_begin();



	local_irq_enable();

	success = __do_fast_syscall_32(regs);



	/* Fetch EBP from where the vDSO stashed it. */

	if (

#ifdef CONFIG_X86_64

		/*

		 * Micro-optimization: the pointer we're following is explicitly

		 * 32 bits, so it can't be out of range.

		 */

		__get_user(*(u32 *)&regs->bp,

			    (u32 __user __force *)(unsigned long)(u32)regs->sp)

#else

		get_user(*(u32 *)&regs->bp,

			 (u32 __user __force *)(unsigned long)(u32)regs->sp)

#endif

		) {



		/* User code screwed up. */

		local_irq_disable();

		regs->ax = -EFAULT;

		prepare_exit_to_usermode(regs);

		return 0;	/* Keep it simple: use IRET. */

	}

	instrumentation_end();

	exit_to_user_mode();



	/* Now this is just like a normal syscall. */

	do_syscall_32_irqs_on(regs);

	/* If it failed, keep it simple: use IRET. */

	if (!success)

		return 0;



#ifdef CONFIG_X86_64

	/*

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