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authorAndrea Arcangeli <andrea@cpushare.com>2007-07-15 23:41:33 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-16 09:05:50 -0700
commitcf99abace7e07dd8491e7093a9a9ef11d48838ed (patch)
tree3b7cfd7c76c2c43e6ae3fdaaff3a50a752072424
parent1d9d02feeee89e9132034d504c9a45eeaf618a3d (diff)
downloadlinux-bcache-cf99abace7e07dd8491e7093a9a9ef11d48838ed.tar.zst
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>
-rw-r--r--arch/i386/kernel/process.c73
-rw-r--r--include/asm-i386/processor.h4
-rw-r--r--include/asm-i386/thread_info.h5
-rw-r--r--include/linux/seccomp.h10
-rw-r--r--kernel/seccomp.c3
5 files changed, 50 insertions, 45 deletions
diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index 06dfa65ad180..6c49acb96982 100644
--- a/arch/i386/kernel/process.c
+++ b/arch/i386/kernel/process.c
@@ -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
@@ -586,33 +620,6 @@ static noinline void __switch_to_xtra(struct task_struct *next_p,
}
/*
- * 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.
*
* We fsave/fwait so that an exception goes off at the right time
@@ -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.
diff --git a/include/asm-i386/processor.h b/include/asm-i386/processor.h
index 94e0c147c165..422cffef00c9 100644
--- a/include/asm-i386/processor.h
+++ b/include/asm-i386/processor.h
@@ -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.
*/
diff --git a/include/asm-i386/thread_info.h b/include/asm-i386/thread_info.h
index 4cb0f91ae64f..54424e045e01 100644
--- a/include/asm-i386/thread_info.h
+++ b/include/asm-i386/thread_info.h
@@ -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.
diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
index d708974dbfe3..262a8dccfa81 100644
--- a/include/linux/seccomp.h
+++ b/include/linux/seccomp.h
@@ -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)
{
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 1dfa8a509726..ad64fcb731f2 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -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;
}