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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: Andrea Arcangeli <andrea@cpushare.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrea Arcangeli 2007-07-15 23:41:33 -07:00 committed by Linus Torvalds
parent 1d9d02feee
commit cf99abace7
5 changed files with 50 additions and 45 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

73
arch/i386/kernel/process.c
View File

@ -538,8 +538,31 @@ int dump_task_regs(struct task_struct *tsk, elf_gregset_t *regs)
return 1;
}
static noinline void __switch_to_xtra(struct task_struct *next_p,
struct tss_struct *tss)
#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 thread_struct *next;
@ -555,6 +578,17 @@ static noinline void __switch_to_xtra(struct task_struct *next_p,
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)) {
/*
* 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;
}
/*
* 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.
*
@ -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
*/
if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW)
|| test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)))
__switch_to_xtra(next_p, tss);
disable_tsc(prev_p, next_p);
if (unlikely(task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV ||
task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT))
__switch_to_xtra(prev_p, next_p, tss);
/*
* Leave lazy mode, flushing any hypercalls made here.

4
include/asm-i386/processor.h
View File

@ -228,6 +228,10 @@ extern int bootloader_type;
#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.
*/

5
include/asm-i386/thread_info.h
View File

@ -137,6 +137,7 @@ static inline struct thread_info *current_thread_info(void)
#define TIF_DEBUG 17 /* uses debug registers */
#define TIF_IO_BITMAP 18 /* uses I/O bitmap */
#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_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_IO_BITMAP (1<<TIF_IO_BITMAP)
#define _TIF_FREEZE (1<<TIF_FREEZE)
#define _TIF_NOTSC (1<<TIF_NOTSC)
/* work to do on interrupt/exception return */
#define _TIF_WORK_MASK \
@ -160,7 +162,8 @@ static inline struct thread_info *current_thread_info(void)
#define _TIF_ALLWORK_MASK (0x0000FFFF & ~_TIF_SECCOMP)
/* 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.

10
include/linux/seccomp.h
View File

@ -16,11 +16,6 @@ static inline void secure_computing(int 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_set_seccomp(unsigned long);
@ -29,11 +24,6 @@ extern long prctl_set_seccomp(unsigned long);
typedef struct { } seccomp_t;
#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)
{

3
kernel/seccomp.c
View File

@ -74,6 +74,9 @@ long prctl_set_seccomp(unsigned long seccomp_mode)
if (seccomp_mode && seccomp_mode <= NR_SECCOMP_MODES) {
current->seccomp.mode = seccomp_mode;
set_thread_flag(TIF_SECCOMP);
#ifdef TIF_NOTSC
disable_TSC();
#endif
ret = 0;
}