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.
Signed-off-by: Mathieu Desnoyers <[email protected]>
CC: Andi Kleen <[email protected]>
CC: Thomas Gleixner <[email protected]>
CC: Ingo Molnar <[email protected]>
CC: H. Peter Anvin <[email protected]>
---
arch/x86/kernel/entry_64.S | 12 ++++++++++++
1 file changed, 12 insertions(+)
Index: linux-2.6-lttng/arch/x86/kernel/entry_64.S
===================================================================
--- linux-2.6-lttng.orig/arch/x86/kernel/entry_64.S 2007-11-13 09:25:25.000000000 -0500
+++ linux-2.6-lttng/arch/x86/kernel/entry_64.S 2007-11-13 09:49:48.000000000 -0500
@@ -268,6 +268,8 @@ sysret_check:
/* Handle reschedules */
/* edx: work, edi: workmask */
sysret_careful:
+ testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP),%edx
+ jnz ret_from_sys_call_trace
bt $TIF_NEED_RESCHED,%edx
jnc sysret_signal
TRACE_IRQS_ON
@@ -279,6 +281,16 @@ 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
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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