[RFC patch 18/20] LTTng Linux Kernel Trace Thread Flag x86

[Mathieu Desnoyers]

Add a thread flag to activate system-wide syscall tracing.

Make x86 support TIF_SYSCALL_TRACE async flag set in entry_32.S/entry_64.S.

x86_64 :

When the flag is inactive upon syscall entry and concurrently activated before
exit, we seem to reach a state where the top of stack is incorrect upon return
to user space.

Fix this by fixing the top of stack and jumping to int_ret_from_sys_call if we
detect that thread flags has been modified.

We make sure that the thread flag read is coherent between our new test and the ALLWORK_MASK test by first saving it in a register used for both comparisons.

Note :
Removed :

        # perform syscall exit tracing
        ALIGN
  syscall_exit_work:
-       testb $_TIF_WORK_SYSCALL_EXIT, %cl
        jz work_pending
        TRACE_IRQS_ON
        ENABLE_INTERRUPTS(CLBR_ANY)     # could let syscall_trace_leave() call
--- 571,578 ----
        # perform syscall exit tracing
        ALIGN
  syscall_exit_work:
+       /* Note, _TIF_KERNEL_TRACE is bit number 9, and so it needs testw and not testb */
+       testw $_TIF_WORK_SYSCALL_EXIT, %cx
        jz work_pending
        TRACE_IRQS_ON
        ENABLE_INTERRUPTS(CLBR_ANY)     # could let syscall_trace_leave() call

because testl now used in mainline since 2.6.30-rc1.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
CC: Andi Kleen <ak@xxxxxx>
CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: H. Peter Anvin <hpa@xxxxxxxxx>
---
 arch/x86/include/asm/thread_info.h |    9 ++++++---
 arch/x86/kernel/entry_64.S         |   12 ++++++++++++
 2 files changed, 18 insertions(+), 3 deletions(-)

Index: linux-2.6-lttng/arch/x86/include/asm/thread_info.h
===================================================================
--- linux-2.6-lttng.orig/arch/x86/include/asm/thread_info.h	2009-04-11 23:57:41.000000000 -0400
+++ linux-2.6-lttng/arch/x86/include/asm/thread_info.h	2009-04-12 00:07:48.000000000 -0400
@@ -82,6 +82,7 @@ struct thread_info {
 #define TIF_SYSCALL_EMU		6	/* syscall emulation active */
 #define TIF_SYSCALL_AUDIT	7	/* syscall auditing active */
 #define TIF_SECCOMP		8	/* secure computing */
+#define TIF_KERNEL_TRACE	9	/* kernel trace active */
 #define TIF_MCE_NOTIFY		10	/* notify userspace of an MCE */
 #define TIF_NOTSC		16	/* TSC is not accessible in userland */
 #define TIF_IA32		17	/* 32bit process */
@@ -105,6 +106,7 @@ struct thread_info {
 #define _TIF_SYSCALL_EMU	(1 << TIF_SYSCALL_EMU)
 #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
+#define _TIF_KERNEL_TRACE	(1 << TIF_KERNEL_TRACE)
 #define _TIF_MCE_NOTIFY		(1 << TIF_MCE_NOTIFY)
 #define _TIF_NOTSC		(1 << TIF_NOTSC)
 #define _TIF_IA32		(1 << TIF_IA32)
@@ -121,18 +123,19 @@ struct thread_info {
 /* work to do in syscall_trace_enter() */
 #define _TIF_WORK_SYSCALL_ENTRY	\
 	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU | _TIF_SYSCALL_FTRACE |	\
-	 _TIF_SYSCALL_AUDIT | _TIF_SECCOMP | _TIF_SINGLESTEP)
+	 _TIF_SYSCALL_AUDIT | _TIF_SECCOMP | _TIF_SINGLESTEP | \
+	 _TIF_KERNEL_TRACE)
 
 /* work to do in syscall_trace_leave() */
 #define _TIF_WORK_SYSCALL_EXIT	\
 	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SINGLESTEP |	\
-	 _TIF_SYSCALL_FTRACE)
+	 _TIF_SYSCALL_FTRACE | _TIF_KERNEL_TRACE)
 
 /* work to do on interrupt/exception return */
 #define _TIF_WORK_MASK							\
 	(0x0000FFFF &							\
 	 ~(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|			\
-	   _TIF_SINGLESTEP|_TIF_SECCOMP|_TIF_SYSCALL_EMU))
+	   _TIF_SINGLESTEP|_TIF_SECCOMP|_TIF_SYSCALL_EMU|_TIF_KERNEL_TRACE))
 
 /* work to do on any return to user space */
 #define _TIF_ALLWORK_MASK ((0x0000FFFF & ~_TIF_SECCOMP) | _TIF_SYSCALL_FTRACE)
Index: linux-2.6-lttng/arch/x86/kernel/entry_64.S
===================================================================
--- linux-2.6-lttng.orig/arch/x86/kernel/entry_64.S	2009-04-11 23:57:41.000000000 -0400
+++ linux-2.6-lttng/arch/x86/kernel/entry_64.S	2009-04-12 00:05:45.000000000 -0400
@@ -528,6 +528,8 @@ sysret_check:
 	/* Handle reschedules */
 	/* edx:	work, edi: workmask */
 sysret_careful:
+	testl $_TIF_KERNEL_TRACE,%edx	/* Re-read : concurrently changed */
+	jnz ret_from_sys_call_trace
 	bt $TIF_NEED_RESCHED,%edx
 	jnc sysret_signal
 	TRACE_IRQS_ON
@@ -539,6 +541,16 @@ sysret_careful:
 	CFI_ADJUST_CFA_OFFSET -8
 	jmp sysret_check
 
+ret_from_sys_call_trace:
+	TRACE_IRQS_ON
+	sti
+	SAVE_REST
+	FIXUP_TOP_OF_STACK %rdi
+	movq %rsp,%rdi
+	LOAD_ARGS ARGOFFSET  /* reload args from stack in case ptrace changed it */
+	RESTORE_REST
+	jmp int_ret_from_sys_call
+
 	/* Handle a signal */
 sysret_signal:
 	TRACE_IRQS_ON

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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