Fix x86_64 TIF_SYSCALL_TRACE race in entry.S
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.
It applies on top of 2.6.23-mm1 or 2.6.23.1. If you think the
implementation is correct, I'll port it to 2.6.24-rc1.
Signed-off-by: Mathieu Desnoyers <[email protected]>
CC: Andi Kleen <[email protected]>
---
arch/x86_64/kernel/entry.S | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
Index: linux-2.6-lttng/arch/x86_64/kernel/entry.S
===================================================================
--- linux-2.6-lttng.orig/arch/x86_64/kernel/entry.S 2007-10-27 14:01:12.000000000 -0400
+++ linux-2.6-lttng/arch/x86_64/kernel/entry.S 2007-10-27 14:01:28.000000000 -0400
@@ -245,9 +245,11 @@ ret_from_sys_call:
/* edi: flagmask */
sysret_check:
GET_THREAD_INFO(%rcx)
+ movl threadinfo_flags(%rcx),%edx
+ testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP),%edx
+ jnz ret_from_sys_call_trace
cli
TRACE_IRQS_OFF
- movl threadinfo_flags(%rcx),%edx
andl %edi,%edx
jnz sysret_careful
CFI_REMEMBER_STATE
@@ -278,6 +280,14 @@ sysret_careful:
CFI_ADJUST_CFA_OFFSET -8
jmp sysret_check
+ret_from_sys_call_trace:
+ 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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