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Commit cf99abac authored by Andrea Arcangeli's avatar Andrea Arcangeli Committed by Linus Torvalds
Browse files

make seccomp zerocost in schedule 



This follows a suggestion from Chuck Ebbert on how to make seccomp
absolutely zerocost in schedule too.  The only remaining footprint of
seccomp is in terms of the bzImage size that becomes a few bytes (perhaps
even a few kbytes) larger, measure it if you care in the embedded.

Signed-off-by: default avatarAndrea Arcangeli <andrea@cpushare.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1d9d02fe

arch/i386/kernel/process.c

+39 −34
Original line number Original line Diff line number Diff line
@@ -538,7 +538,30 @@ int dump_task_regs(struct task_struct *tsk, elf_gregset_t *regs) 
	return 1;

	return 1;

}

}





static noinline void __switch_to_xtra(struct task_struct *next_p,

#ifdef CONFIG_SECCOMP

void hard_disable_TSC(void)

{

	write_cr4(read_cr4() | X86_CR4_TSD);

}

void disable_TSC(void)

{

	preempt_disable();

	if (!test_and_set_thread_flag(TIF_NOTSC))

		/*

		 * Must flip the CPU state synchronously with

		 * TIF_NOTSC in the current running context.

		 */

		hard_disable_TSC();

	preempt_enable();

}

void hard_enable_TSC(void)

{

	write_cr4(read_cr4() & ~X86_CR4_TSD);

}

#endif /* CONFIG_SECCOMP */



static noinline void

__switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,

		 struct tss_struct *tss)

		 struct tss_struct *tss)

{

{

	struct thread_struct *next;

	struct thread_struct *next;
@@ -555,6 +578,17 @@ static noinline void __switch_to_xtra(struct task_struct *next_p, 
		set_debugreg(next->debugreg[7], 7);

		set_debugreg(next->debugreg[7], 7);

	}

	}





#ifdef CONFIG_SECCOMP

	if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^

	    test_tsk_thread_flag(next_p, TIF_NOTSC)) {

		/* prev and next are different */

		if (test_tsk_thread_flag(next_p, TIF_NOTSC))

			hard_disable_TSC();

		else

			hard_enable_TSC();

	}

#endif



	if (!test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {

	if (!test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {

		/*

		/*

		 * Disable the bitmap via an invalid offset. We still cache

		 * Disable the bitmap via an invalid offset. We still cache
@@ -585,33 +619,6 @@ static noinline void __switch_to_xtra(struct task_struct *next_p, 
	tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;

	tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET_LAZY;

}

}





/*

 * This function selects if the context switch from prev to next

 * has to tweak the TSC disable bit in the cr4.

 */

static inline void disable_tsc(struct task_struct *prev_p,

			       struct task_struct *next_p)

{

	struct thread_info *prev, *next;



	/*

	 * gcc should eliminate the ->thread_info dereference if

	 * has_secure_computing returns 0 at compile time (SECCOMP=n).

	 */

	prev = task_thread_info(prev_p);

	next = task_thread_info(next_p);



	if (has_secure_computing(prev) || has_secure_computing(next)) {

		/* slow path here */

		if (has_secure_computing(prev) &&

		    !has_secure_computing(next)) {

			write_cr4(read_cr4() & ~X86_CR4_TSD);

		} else if (!has_secure_computing(prev) &&

			   has_secure_computing(next))

			write_cr4(read_cr4() | X86_CR4_TSD);

	}

}



/*

/*

 *	switch_to(x,yn) should switch tasks from x to y.

 *	switch_to(x,yn) should switch tasks from x to y.

 *

 *
@@ -689,11 +696,9 @@ struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct tas 
	/*

	/*

	 * Now maybe handle debug registers and/or IO bitmaps

	 * Now maybe handle debug registers and/or IO bitmaps

	 */

	 */

	if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW)

	if (unlikely(task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV ||

	    || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)))

		     task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT))

		__switch_to_xtra(next_p, tss);

		__switch_to_xtra(prev_p, next_p, tss);



	disable_tsc(prev_p, next_p);





	/*

	/*

	 * Leave lazy mode, flushing any hypercalls made here.

	 * Leave lazy mode, flushing any hypercalls made here.

include/asm-i386/processor.h

+4 −0
Original line number Original line Diff line number Diff line
@@ -228,6 +228,10 @@ extern int bootloader_type; 




#define HAVE_ARCH_PICK_MMAP_LAYOUT

#define HAVE_ARCH_PICK_MMAP_LAYOUT





extern void hard_disable_TSC(void);

extern void disable_TSC(void);

extern void hard_enable_TSC(void);



/*

/*

 * Size of io_bitmap.

 * Size of io_bitmap.

 */

 */

include/asm-i386/thread_info.h

+4 −1
Original line number Original line Diff line number Diff line
@@ -137,6 +137,7 @@ static inline struct thread_info *current_thread_info(void) 
#define TIF_DEBUG		17	/* uses debug registers */

#define TIF_DEBUG		17	/* uses debug registers */

#define TIF_IO_BITMAP		18	/* uses I/O bitmap */

#define TIF_IO_BITMAP		18	/* uses I/O bitmap */

#define TIF_FREEZE		19	/* is freezing for suspend */

#define TIF_FREEZE		19	/* is freezing for suspend */

#define TIF_NOTSC		20	/* TSC is not accessible in userland */





#define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

#define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

#define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)

#define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
@@ -151,6 +152,7 @@ static inline struct thread_info *current_thread_info(void) 
#define _TIF_DEBUG		(1<<TIF_DEBUG)

#define _TIF_DEBUG		(1<<TIF_DEBUG)

#define _TIF_IO_BITMAP		(1<<TIF_IO_BITMAP)

#define _TIF_IO_BITMAP		(1<<TIF_IO_BITMAP)

#define _TIF_FREEZE		(1<<TIF_FREEZE)

#define _TIF_FREEZE		(1<<TIF_FREEZE)

#define _TIF_NOTSC		(1<<TIF_NOTSC)





/* work to do on interrupt/exception return */

/* work to do on interrupt/exception return */

#define _TIF_WORK_MASK \

#define _TIF_WORK_MASK \
@@ -160,7 +162,8 @@ static inline struct thread_info *current_thread_info(void) 
#define _TIF_ALLWORK_MASK	(0x0000FFFF & ~_TIF_SECCOMP)

#define _TIF_ALLWORK_MASK	(0x0000FFFF & ~_TIF_SECCOMP)





/* flags to check in __switch_to() */

/* flags to check in __switch_to() */

#define _TIF_WORK_CTXSW (_TIF_DEBUG|_TIF_IO_BITMAP)

#define _TIF_WORK_CTXSW_NEXT (_TIF_IO_BITMAP | _TIF_NOTSC | _TIF_DEBUG)

#define _TIF_WORK_CTXSW_PREV (_TIF_IO_BITMAP | _TIF_NOTSC)





/*

/*

 * Thread-synchronous status.

 * Thread-synchronous status.

include/linux/seccomp.h

+0 −10
Original line number Original line Diff line number Diff line
@@ -16,11 +16,6 @@ static inline void secure_computing(int this_syscall) 
		__secure_computing(this_syscall);

		__secure_computing(this_syscall);

}

}





static inline int has_secure_computing(struct thread_info *ti)

{

	return unlikely(test_ti_thread_flag(ti, TIF_SECCOMP));

}



extern long prctl_get_seccomp(void);

extern long prctl_get_seccomp(void);

extern long prctl_set_seccomp(unsigned long);

extern long prctl_set_seccomp(unsigned long);
@@ -29,11 +24,6 @@ extern long prctl_set_seccomp(unsigned long); 
typedef struct { } seccomp_t;

typedef struct { } seccomp_t;





#define secure_computing(x) do { } while (0)

#define secure_computing(x) do { } while (0)

/* static inline to preserve typechecking */

static inline int has_secure_computing(struct thread_info *ti)

{

	return 0;

}





static inline long prctl_get_seccomp(void)

static inline long prctl_get_seccomp(void)

{

{

kernel/seccomp.c

+3 −0
Original line number Original line Diff line number Diff line
@@ -74,6 +74,9 @@ long prctl_set_seccomp(unsigned long seccomp_mode) 
	if (seccomp_mode && seccomp_mode <= NR_SECCOMP_MODES) {

	if (seccomp_mode && seccomp_mode <= NR_SECCOMP_MODES) {

		current->seccomp.mode = seccomp_mode;

		current->seccomp.mode = seccomp_mode;

		set_thread_flag(TIF_SECCOMP);

		set_thread_flag(TIF_SECCOMP);

#ifdef TIF_NOTSC

		disable_TSC();

#endif

		ret = 0;

		ret = 0;

	}

	}